March 28, 2016
Monday-Friday: Night-Day…And How an Inside Slider Works
Scattered snow showers will taper off a bit tonight under a cold and unstable airmass. The low pressure center that brought our inside slider will move slightly to the south but will be close enough to keep showers in the forecast. Temperatures will warm Tuesday but will still be cold enough to allow for snow levels to reach the valley floors (although little to no additional accumulation is expected). unsettled conditions will last through Wednesday with a chance of rain or snow showers, but then conditions warm very quickly toward the end of the week, with high temperatures reaching the low 70s by Friday and staying there through the weekend.
We talked earlier about the “Inside Slider” weather pattern, as is usual, it was full of surprises. A Slider is a weather pattern caused by a low pressure center that drops down from the north, and bypasses the mountains so we don’t get shadowed out here on the east side of the Sierra. Even though they can vary greatly in strength, it is not unusual that the band dropping down from the north will enhance just as it gets to the Reno area. Tomorrow I’ll tell you why that happens.
March 25, 2016
“Inside Slider” Coming?…And How Far West Do We Look for Weather?
A sunny and mild Saturday will give way to an Easter Sunday that will likely stay dry, but will start to get windy in the afternoon ahead of a series of moderate storms coming in early next week. High temperatures Saturday will drop a bit but still reach the low 60s before warming into the mid to upper 60s Sunday. But late Sunday night into Monday morning, an “Inside Slider” type of storm will drop out of the north, bringing a chance of snow all the way to the valleys perhaps in time for the Monday morning commute. These types of storm system are notoriously difficult to predict, but can put a quick inch or two down if they hold together. Unsettled and cool weather sticks around through mid-week before things warm back up by the weekend.
Jerry asks: “How far west do you look to get a handle on upcoming weather? It does appear that as weather moves east the highs and lows don’t disappear… they just sort of dance around each other. So it seems reasonable that looking west like at China or Russia and looking at their stuff you might see what’s soon to be in our back yard.”
If you really want to get technical, I look all around the globe (at least the entire northern hemisphere), since the whole atmosphere is interconnected. But I look most intently at what is going on from here out into the central Pacific, and less so at the rest of the Pacific.
There are some exceptions to this: The far western Pacific can be of great interest. Often when we get a deepening low pressure over Japan it foretells a storm dropping over us about four days later. It doesn’t always work, but it’s not a bad rule of thumb.
I learned that trick from Tom Cylke, now retired from the National Weather Service. Tom wrote in to tell me that this method dates back to the 1950’s from a meteorologist named Hovmoller. It is only effective if the global long wave pattern is set up a certain way (which can be a challenge to determine in itself), but was quite a tool in the days before computer models and satellites.
March 23, 2016
Warmer Week (for now)…And What is an “Inch of Mercury?”
Dry and warmer conditions will carry us into the weekend. A broad ridge of high pressure will set up across the west coast pushing the storm track well to our north. Temperatures will climb into the 60s and stay there through the weekend. Skies will range from mostly sunny to partly cloudy until Sunday when the next storm system will approach, kicking up winds late Sunday, and bringing a good chance of mountain rain and snow (and to a lesser extent to the valleys) late Sunday through Monday.
I’ve had many ask me just what is meant by an “inch of mercury,” and how that relates to pressure. Whereas a Pascal is a calculated figure equal to a Newton per square meter (you can ask, but that’s for another column), an inch of mercury is a unit derived by the readings of the first instruments used to measure air pressure.
Keep in mind both air and liquids are “fluids” when it comes to how they exert pressure on objects. If you dive down to the bottom of a deep swimming pool, you are likely to feel the pressure increase on your ears, just as your ears pop when travelling over the mountains. A column of air an inch square extending out to the top of the atmosphere (over 20 miles) weighs about 14.5 pounds, and therefore exerts a pressure of 14.5 pounds per square inch (1 bar) at sea level. Because liquids are much denser, if you filled that same one inch square column with water, it would only take about 34 feet to weigh the same as a 20+ mile high column of air. In fact, you could make a barometer out of water by filling a 35+ foot glass test tube with water, invert it in an open pan of water, and measure how high the column of water stays in the closed end. But that wouldn’t fit into most people’s living rooms, so we use mercury, which is 13.6 times denser than water, and only takes about 30 inches in your column to weigh the same as one atmosphere. So “an inch of mercury” is the pressure equivalent of about 1/30th of an atmosphere.
March 22, 2016
Drier and Warmer…And Know Your Barometer Units (Pt. 2)
After a cold front dropped our temperatures into the 40s Tuesday, warmer air will move back into the region as a broad ridge of high pressure builds up across the west coast. There will be occasional cloudiness for the rest of the work week, but temperatures will climb into the upper 50s Wednesday, and then peak out in the low to mid-60s through the rest of the week. Come Sunday, we are in for a near repeat of last with another storm system coming in that will kick up some winds and bring another round of snow to the mountains with a chance of valley showers.
Yesterday, I told Marci to set her son’s barometer to the same inches of mercury reading the airport reports. But she said “It’s marked in ‘hPa,’ not inches. Does that make a difference?”
Indeed it does. hPa stands for hectopascal, or 100 Pascals. A Pascal is the standard metric unit of pressure. One atmosphere of pressure (the approximate pressure you will find at sea level) equals just over 100,000 Pascals. So a hectopascal is roughly equal to one thousandth of an atmosphere, and is exactly equal to one millibar.
It actually makes more sense to use hPa for pressure when it comes to the international community, but we Yanks just have to be different, and we’ve adopted inches of mercury as our public standard.
March 21, 2016
One More Shot of Winter…And Barometer Questions (Pt. 1)
Now that spring has officially begun, as often happens around here the weather will turn back to a wintrier pattern for a bit. A fairly cold low pressure center will push onshore passing through the northern part of the Silver State, dropping temperatures into the 40s and giving us a chance of rain or snow showers. I don’t expect any significant valley accumulations, although an inch is possible up in the foothills. The mountains should see more significant accumulations, as much as 8” on the peaks, with a few inches at most around the lake itself.
The system blows through the region fairly quickly, and by Wednesday the skies should partly clear and conditions should dry out in general. Temperatures warm back into the 50d Wednesday and then climb into the 60s Thursday through the weekend.
I get the following request a lot. Marci wrote me to tell me that her son Luke just got a new weather set. (I hear tell Luke is after my job.) She knew that the barometer needed to be set to Reno’s elevation, and wondered how to calibrate it. I told her to set it to 29.89 inches of mercury (the pressure at the time), and Bob’s your uncle, Luke will be on his way to meteorological harmony. But there was another issue, which I’ll tackle tomorrow.
March 18, 2016
Should We Turn On the Sprinklers Yet?
With the warming temperatures of late, a lot of people have been asking if it is time to turn the sprinklers back on again. In a nutshell, I’d say no. There are several reasons for this. To begin with, even though the last few days have been warm and dry, the ground is still relatively moist due to the storms of the winter. One way to tell is to take a screwdriver and push it into your lawn or garden bed, and see how easily it goes in. Ground that is too dry will become very hard and it will be difficult to push the screwdriver in. If you do have ground that dry, I would recommend doing some light hand watering.
The reason for caution is that hard freezes are still historically common this time of year, and can occur through April, and sometimes even later. That not only can be hard on irrigation systems, but you don’t want to encourage your plants, trees and grass to come out of hibernation any more than they have to. Many a fruit crop has been lost due to early blooms that get hit with a hard freeze.
March 17, 2016
Warm and Sunny End to Winter…And Why It Snows More in Elko (Pt 3)
While we won’t see record temperatures, the last two days of winter will be decidedly spring-like. Sunny skies with highs in the low 70s on Friday will continue into Saturday, although a few afternoon clouds will probably roam across the region Saturday Afternoon. But on Sunday a cold front will try to get across the mountains, kicking up some gusty winds, and some rain and high elevation snow, mainly to the mountains. Rain showers could spill over into the valley late Sunday and early Monday, but the rain shadow will limit how much, if any, we get.
So why does eastern Nevada get more snow than the Reno area? From a precipitation standpoint, they are really not in the rain shadow of the Sierra nearly as much as we are. So as storms come in and cross the Sierra, they have a chance to reform farther east without having to overcome the suppressing effect of the down slope winds. Even though overall there may be less moisture in the air to the east, it’s easier to get what moisture there is out of the air without the rain shadow effect.
March 16, 2016
Warm End To Winter…And Why Eastern Nevada is Colder (Pt. 2)
A warm and mostly sunny week ahead. Spring officially starts Saturday night at 9:30 pm, but the last several days of winter will be decidedly spring like. High temperatures in the upper 60s to low 70s through Sunday will give way to a moderate winter storm Sunday night into Monday, which will bring a chance of valley rain and high elevation snow to the mountains, and we will see valley temperatures drop back to the 50s for the first half of next week.
Chuck wondered why eastern Nevada was colder and snowier than the western. In terms of the temperature, it’s mostly due to the fact that by the time you get to the eastern side of the state the airmass has become a little more continental in nature. We still have a little bit of marine influence from the Pacific Ocean here, although it’s not nearly as pronounced as on the western side of the Sierra. A continental airmass tends to be a little colder in the winter due to a little less moisture in the air.
But if the air is drier in the east, why is it snowier? I’ll answer tomorrow.
March 15, 2016
70s later this week…And Why is Eastern Nevada Colder and Snowier Than Western?
A much warmer and calmer week is ahead of us, as a ridge of high pressure builds onshore and stays nearly through the week. Mostly sunny skies (with a few afternoon clouds) will cover the area through Friday as temperatures warm to the low 60s Wednesday, the upper 60s by Friday and could hit 70 over the weekend. By the beginning of next week, the ridge breaks down and could allow a storm to move through on Monday, dropping the temperatures back into the 50s.
Chuck Lacy sent me the following query: “I’ve lived in Carson Valley since 1990 and have noticed one thing that’s pretty constant, and that is that the winter weather in eastern Nevada is always quite a bit colder and gets more snow than we do out here in the west. I don’t believe it’s the elevation, with Elko about the same elevation as our area (just over 5,000 feet) and Ely about the same as Tahoe. So, can you explain the dynamics of this phenomenon for me?” There are a couple of reasons, and I’ll dive in starting tomorrow.
March 14, 2016
Warmer Week…And Is Graupel “Corn Snow?”
This will be a much different week than the last. A ridge of high pressure will build into the west coast, kicking the storm track well to our north and bringing back sunnier and warmer conditions. A few clouds left over on Tuesday will likely clear out on Wednesday, and the skies should stay sunny through the rest of the work week. Temperatures will rise to the upper 50s Tuesday and continue to climb into the mid-60s into and through the weekend.
One type of snow (graupel seems to be a crowd favorite) piqued Jeanne’s interest: “You referred to graupel… is this the same as “corn snow”? What would be the difference?”
It isn’t the same. One is a type of snow that falls… the other a type of snow after it falls. As a skier, I always considered corn snow to be snow that had gone through several freeze-thaw cycles, creating a crumbly this surface layer that’s easier to get an edge on. After researching it a bit, I find that I remembered correctly. Corn snow can initially fall in any state, but only becomes such after several days of thermal cycles. It is a highly prized spring skiing condition, when light fluffy powder conditions become rare.
March 11, 2016
Lots of weather to get ready for this weekend. Winds will pick up Saturday gusting as high as 60 mph in the afternoon (kicking off a Wind Advisory) ahead of a cold front which will bring heavy snow to the mountains (kicking off a Winter Storm Warning running from mid-day Saturday through Monday morning.) Travel over the mountains the second half of the weekend will be challenging with high winds combining with the heavy snow to produce whiteout conditions. By the end of the weekend, total mountain snowfalls could exceed three feet on the peaks, and amounts in the Sierra Valleys, which will vary greatly depending on elevation, will likely range from several inches to a foot or more.
In the valleys, the high winds will initially limit how much precipitation we will see getting over the mountains, but a slight chance of Saturday showers of rain becomes a likely chance on Sunday and Sunday night. Snow levels will drop close to the valley floors by early Monday, but it is unlikely we will see significant accumulations below the 5,000’ elevation.
March 10, 2016
Winter Storm Watch Late This Weekend
It is still looking like a fairly stormy pattern will continue off and on through the weekend and into the first of next. For Friday, a moderate storm front will bring rain and snow to the mountains (snow level between 6,500-7,000’) and a chance of scattered rain to the valleys. Temperatures will top out near 60 degrees. Saturday, a brief break occurs between storms, and Saturday night the next storm arrives, bringing strong winds, mountain snow through Sunday night (A Winter Storm Watch has been issued) and cooler temperatures. For the valleys, the rain might turn to snow by early Monday morning, but it is unlikely that there will be any significant accumulations down low. But travel over the mountains will be challenging Friday night and then late Saturday night through Monday midday. Total snow accumulations will vary greatly depending on elevation, but by Monday the lake could potentially accumulate a foot or more, and the mountaintops could see upwards of an additional three feet.
It comes at a good time, as total snowpack water contents have dropped to just below average for this time of year, but should rebound nicely by next week.
March 9, 2016
Double Wave of Storms This Weekend
As we head into the weekend, there will be two different weather events which will impact the mountains more than the valleys, but will likely leave their marks everywhere. Initially, a Wind Advisory is posted for western Nevada and the Sierra Thursday as a cold front approaches and moves on the coast. There’s only a slight chance (20%) of any showers Thursday in Reno and only slightly better chance (30%) on Friday, although the mountains do have a better shot with relatively high snow levels. There is a brief break Saturday morning before a colder and more vigorous storm comes in Saturday night and Sunday. Snow amounts could be very significant for the mountains in this second wave, with a foot or more eventually accumulating at lake level, with the crests potentially totaling up amounts on the order of a couple of feet or more.
The snow level drops enough Monday morning so that we might see some snow in the lower valley elevations, but it is unlikely there will be significant accumulations until you get up into the upper foothills.
March 8, 2016
Storms Off and On…And Rain Shadow Explained (Final)
It still looks like a petty active weather pattern for the rest of the week. A weak storm system should bring scattered showers through Wednesday morning, with snow levels rising to about 7,000’ through the day. Thursday should see us between systems, although a stray shower isn’t out of the question. As we head into the weekend, some colder and stronger storm fronts will move through, bringing valley rain and mountain snow on Friday and Sunday, with a brief break on Saturday.
The air becomes “dry” on the lee side from a relative humidity standpoint, since the temperatures warm as the air descends and compresses.
When you are talking about a rain shadow, many people mistakenly think that the Sierra “block” or “stop” the moisture from getting over the mountains. That’s not really how it works. Just as lifting air causes precipitation, descending air heats up, which evaporates the clouds and suppresses precipitation. As the air flows up the west side of the mountains, it increases rain and snow, but as it flows down the back side into western Nevada, it heats up and kills the precipitation producing process, unless some other lifting process is strong enough to overcome the backside drop. So the mountains don’t block the moisture… it just turns back into vapor and stays in the air, bypassing us until it gets lifted by some other process further to the east.
March 7, 2016
Another Active Week Ahead…And What’s Up With This Rain Shadow? (Pt. 1)
While there isn’t any one major storm coming through the region, this week will be quite active with an almost daily procession of systems starting Wednesday. For the short term, Tuesday will give us a brief break in the action with a short lived high pressure ridge moving through. It will be followed by another low moving down from the northwest, bringing a slight chance of showers Wednesday, although its path is a little too far to the north to really benefit us too much. Each successive day brings a chance (though not a sure bet on any individual system) of valley rain and mountain snow right through the weekend.
I talk about the “rain shadow” a lot around here… not surprising since we are on the lee side of a major mountain range. If you have ever wondered why we are in a desert environment on this side of the mountains and things are a lot more lush (lusher?) on the west side, but never really understood why, read on.
Before we can understand how a mountain can cause a decrease in precipitation, first we need to talk a bit about what causes rain and snow in the first place. In an oversimplified nutshell, precipitation can occur if you take moist air and cool it to the point to where the water vapor in the air condenses back to a liquid (or solid…ice…but for the sake of this discussion, we’ll combine both states here.) This forms clouds, which if the condensation continues, will form droplets big enough to fall out as rain. The best way to cool air is to force it higher up in the atmosphere, where the drop in air pressure causes a drop in temperature.
In fact, much of my job as a meteorologist is wrapped up in trying to figure out where the upward vertical motion is and will occur. Air moves up… you can get rain. So how does this forcing upward happen naturally? This can occur several ways. A cold front will burrow under warmer moist air, lifting it. Converging airmasses at the lower levels of the atmosphere will have nowhere to go but up, and diverging airmasses in the upper levels of the atmosphere will draw up air from the lower levels. But land can also play an important part in vertical motion of the atmosphere. The Sierra Nevada will take moist air coming in off the Pacific and lift it, greatly increasing precipitation in the mountains.
March 4, 2016
Winter Storm Warning for the Sierra…High Wind Warning for the Valleys
Travel over the mountains this weekend will be quite a challenge. A Winter Storm Warning goes into effect in the mountains starting at 10 pm Saturday and it lasts 36 hours until 10 am Monday morning. Total mountain snowfall is difficult to be very precise about because the snow levels will start out very high (8,000’+) and will drop late Saturday night/Sunday morning to below Lake Tahoe elevation, and could come close to the Valley floor by then. Overall, snow amounts ranging from 1-3 feet or more in the upper elevations are possible by Monday.
For the Reno area, a High Wind Warning goes into effect Saturday afternoon, with 65 mph gusts possible. These strong winds will create a pretty effecting rain shadow in the valley, but some spillover rainfall is likely, especially on the western side of the valley. Rainfall becomes more likely late Saturday night into Sunday, and some snow might mix in with the rain on Sunday. Showers will continue into Monday as the temperatures start in the 60s Saturday and will crash into the 40s Sunday and Monday.
A break Tuesday and Wednesday ends with another storm slated to arrive Thursday or Friday.
March 3, 2016
Strong Storm Heading for the Mountains
A series of Pacific storms will move into the region starting this weekend, causing some travel challenges over the mountains. A Winter Storm Watch is in effect for the mountains starting Saturday evening into Monday morning. For Friday, the valley could see some isolated rain showers, although we will see considerable shadowing. Snow levels will start out quite high (~8,000’) and will stay there until a cold front moves through Saturday night, after which they will drop to below Lake Tahoe, and will get near the valley floors Sunday, although I don’t expect significant accumulations on the floor. Snow accumulations in the mountains could range from 1-3 feet near the peaks with lesser amounts at Lake Tahoe level. Snow showers will taper off Monday, and it now appears there will be a break Tuesday and Wednesday before the next storm moves in around Thursday.
Winds will be very strong ahead of the front, gusting to 65 mph in Reno Saturday afternoon and into triple digits on the mountain ridges. Whiteout conditions over the passes will create dangerous driving late Saturday and Sunday.
March 2, 2016
Strong Mountain Storms Headed Our Way
While the next couple of days could give us some scattered showers here and there (with high snow levels), a much stronger series of storms will move through the region starting the middle of the weekend. On both Thursday and Friday, a couple of weak frontal systems will stall out across the region, giving the valleys a slight chance of showers and mountain snow above 7,500-8,000’. Late in the day on Saturday, a stronger and colder storm moves in with high winds, possible heavy rain and very likely heavy snow for the mountains. Travel over the mountains is expected to be very challenging Saturday night through Sunday. That storm is cold enough to bring snow levels close to the valley floors on Sunday.
Over the next several days, more storm fronts should bring additional moderate to heavy snow to the mountains, and looking beyond into late next week, the storm track appears to be very favorable for additional storms. It’s too early to say if it’s a “Miracle March,” but it’s a great start.
March 1, 2016
Storms Returning…And What Happened to El Niño? (Pt. 2)
It is looking more and more like the weather pattern will change for the active, and a little sooner than originally thought. Wednesday will still be mostly sunny, dry and warm ahead of the first weak cold front that moves through the region Thursday. There is only a slight chance that first system will be able to overcome the shadowing effect of the mountains and produce valley rain, but the mountains should pick up some high elevation snow Thursday and Friday. A series of colder systems move through the region over the weekend, and it looks like the active storm track will stick around at least halfway through the next week.
Perhaps apropos of the above forecast, the easy answer to “What happened to El Niño?” is “Nothing at all.” El Niño has remained in the equatorial eastern Pacific throughout our dry February (although it has probably peaked), but it is very important to remember that El Niño isn’t the tail that wags the whole weather dog. There are numerous other factors that come into play. It’s very common during even strong El Niños that we have a dry month amongst wet ones, and the wet periods can be cyclical within each season. And all indications point to entering another one.
February 29, 2016
Storms Returning Late in Week…And What Happened to El Niño? (Pt. 1)
While it may take until the end of the weekend, there are some signs that a more active storm pattern will return to the region. In the short term, the west coast ridge of high pressure will continue to keep us warm and dry, nudging storms too far to the north to give us much chance of getting any water out of them. High temperatures will rise to near 70 degrees Tuesday and Wednesday before falling back to the low 60s on Thursday. Late Saturday, the ridge finally breaks down to allow the first of what could be several storms to move into the region, with valley rain a decent possibility, but mountain rain and snow almost a sure bet on Sunday.
Since February is now in the books, and not impressively so from a precipitation standpoint, I’ve been getting a lot of questions like to following from former Lieutenant Governor Sue Wagner: “El Niño…Where is it? Has it gone away?”
It’s easy to get lulled into the belief that once there’s a El Niño out there, there will be a continuous series of storms throughout the winter, but it ain’t necessarily so. More on this tomorrow.
February 26, 2016
Dry Weekend…And Why the Sun Feels So Hot (Final)
While we will see variable amounts of cloudiness over the weekend, it’s unlikely they will produce any rain, at least down here in the valley. A weak cold front will drop Saturday high temperatures a few degrees, but we should still see daytime highs in the 60s through the weekend. The next chance for showers (and it is only a slight one at this point) comes midway through next week.
An Erupting Prominence. Prominences are huge clouds of relatively cool, dense plasma suspended in the Sun?s hot, thin corona. Like this large, twirling prominence, they can sometimes erupt and escape the Sun?s atmosphere. SOHO, January 18, 2000
So while the sun can heat the air a little by conduction, it is a lot more efficient at transferring energy to your skin by radiation. Radiation from the sun travels through air relatively unscathed (the air only absorbs a minor amount of the sun’s radiation), and when it hits you, it excites the molecules of your skin, generating heat. That’s why you feel so much hotter if you are in direct sunlight as opposed to being in the shade. Even though it may not seem like it, if you measure the air temperature in and out of the sun, there’s almost no difference. Air is mostly diathermic, which means it allows energy to pass through it without being affected by it.
Many will disagree with that, and they might seek to prove their point by taking a thermometer and laying it in the sun. See?! Look at how the reading immediately rises when it is in the sun. The air must be warmer.
But here’s the problem: While the reading on the thermometer will be much higher in the direct sunlight, that doesn’t mean the air temperature is higher, only that the temperature of the thermometer is higher. Just as the sun’s radiation heats your skin and makes it hotter than the surrounding air, so also it heats the thermometer casing. That’s why it is so important to place your thermometer in a well ventilated, shaded location in order to assure an accurate air temperature reading.
February 25, 2016
Mostly Dry and Warm…And Why the Sun Feels So Hot (Pt. 2)
It still doesn’t look like there’s much of a chance of any showers as we go through the weekend. Temperatures will spike on Friday (into the low 70s) ahead of a weak cold front which will kick up some brisk winds in the afternoon, but most of the precipitation from the front will likely stay to the north of the Reno area. Temperatures will drop Saturday into the low 60s and will fall a bit more into the upper 50s on Monday as another weak cold front passes through Sunday night.
So why does 65 on a sunny day feel so much warmer than the same on a cloudy? The sun can heat you up in two ways. First (and this is how it heats thermometers that read that 65 degrees mentioned above), the sun can heat the air, either directly or indirectly, and then the air transfers that heat to your body by direct contact. That’s called heat transfer by conduction. But the air isn’t really that efficient in conducting heat. But the sun does have a secret weapon when it comes to heating things up: radiation. More on this tomorrow.
February 24, 2016
Warm and (Mostly) Dry…And What Makes the Sun Feel So Hot? (Pt. 1)
Temperatures will run well above average for the next couple of days as the west coast ridge of high pressure resists the attempts of offshore weather systems to break it down. Variable amounts of high cloudiness will still come through the region Thursday and Friday ahead of a weak cold front that will give us a slight chance of an isolated shower north of I-80 Friday night. The front will kick up some relatively strong winds Friday, and will drop our temperatures from the upper 60s Thursday and Friday to the low 60s on Saturday. Another weak system moves through late Sunday into Monday bringing another slight chance of showers.
An Erupting Prominence. Prominences are huge clouds of relatively cool, dense plasma suspended in the Sun?s hot, thin corona. Like this large, twirling prominence, they can sometimes erupt and escape the Sun?s atmosphere. SOHO, January 18, 2000
Our latest sun breaks were probably the impetus for the following: “Our high desert summer sun is intense. What is it about the sun that makes it so physically draining while one is lounging about in a deck chair, but when the temperature is only 65 degrees?” I’ll refrain from talking about spending too much time lounging in deck chairs, and tell you why direct sunshine feels so hot. Tomorrow, I’ll tell you of two different ways how the sun can heat you up.
February 23, 2016
A Lot Warmer…And More Snow Records (Final)
Once again the weather will remain dry through the rest of the week thanks to a healthy ridge of high pressure built up across the west coast. Temperatures will warm into the mid to upper 60s through Friday before easing back to the low 60s over the weekend. Skies will range from sunny to occasional high cloudiness.
Speaking of snowfall records, in Montana back in 1887, it wouldn’t take long to set records if a wild snowstorm had just lasted a little longer. During this storm, the largest snowflakes ever recorded fell over an area of several square miles, and were described as being “larger than milk pans”. Failing to find “milk pans” in the International Standards of Weights and Measures, they were measured by more a mundane method (a ruler), and found to be 15 inches across, and 8 inches thick!
Now if all of this depresses you, and leaves you yearning for some more snow coming our way, take heart. Some of our best snow events have taken place from the middle of February through March.
At least enough to fill up a few milk pans.
February 22, 2016
Dry and Warm…And More Snowfall Records (Pt. 2)
This will be a very mild and uneventful weather week. A large ridge of high pressure is building in offshore which will deflect the energy of any Pacific storms up to our north. Temperatures will climb from the mid-50s Tuesday into the upper 60s by the end of the work week before a low energy system moves in over the weekend, giving us only a slight chance of a shower on Saturday.
Continuing talk about some snowfall records, for years the greatest 12 month snowfall record was held by the Paradise Ranger Station on Washington’s Mount Rainier. Between February 19 of 1971 and 1972, a total of 1,122 inches of snow fell.
But that mark was eclipsed in the winter of 1998-1999 at Mt. Baker Ski Area in Washington, when a total of 1,140 inches were recorded. It took a while for the National Climatic Data Center to verify the record amount, scrutinizing the measuring techniques, most likely because ski areas are somewhat notorious for inflating snowfall figures. Either way, the two top seasonal snowfalls have curiously occurred in the Cascades Mountains in Washington. Tomorrow, world-record snowflakes!
February 19, 2016
Dry Week Ahead…And the Demise of the Blob (Final)
It looks like we will go back into an extended dry stretch again as a broad ridge of high pressure builds back across the west coast. Clouds will decrease throughout the region Saturday, and the skies should be mostly clear for a few days thereafter. Temperatures will climb from the mid-50s Saturday to the low 60s on Sunday, and will likely continue to rise into the mid-60s by the middle of next week.
The last couple of days we’ve been talking about the demise of “The Blob.” Caused by “The Ridiculously Resilient Ridge” of high pressure off the coast of the western US, it’s hard to say whether the Blob (a very warm pool of water off our coast) caused the drought, or was a reflection of the RR Ridge which caused the drought and created the warm water in the Blob. Certainly the ridge was the chief factor in the previous couple of dry winters, but the warm water created by the ridge also very likely reinforced the ridge, which is why some drought patterns can last for several years. Fortunately, other global factors, including our El Niño, finally overcame our blocking pattern, and the Blob is dead…at least for now.
February 18, 2016
Drying Up…and The Demise of “The Blob” (Pt. 2)
While the mountains could see some more snow on Friday (and a rain shower in the valley in the afternoon isn’t out of the question), most of the wintry weather of late will ease as we head into the weekend. There is one more weak storm system moving in Friday afternoon, but the dynamics aren’t strong enough to have much left over for the valley to overcome the rain shadow effect. The mountains could potentially see a couple of additional inches. As we head into the weekend, conditions will stabilize and slowly warm up, from the low 50s on Saturday to near 60 degrees by Monday.
Yesterday, I mentioned that “The Blob” has apparently come to an end. The Blob is the descriptive if decidedly unscientific name given to a large persistent area of anomalously warm water off the coast of the Pacific Northwest which had been there for the last couple of years. Caused by the “RRR” (Ridiculously Resilient Ridge…and no, I’m not making up the names), the Blob was a reflection and possibly a reinforcer of the ridge of high pressure that was the main cause of at least the last two years of drought. Tomorrow, I’ll talk a bit about what this might mean in the future.
February 17, 2016
Return to Winter…And the Demise of “The Blob.”
The strong winds will slowly abate Thursday, but the strong cold front responsible will bring snow to the valley floors and leave behind a foot or more of snow in the mountaintops. A mountain Winter Storm Warning is in effect until noon Thursday after which snow will decrease to showers. In the valley, accumulations could be limited due to the ground being so warm the past several days, but some foothill accumulations are possible above 5,000’. The strong winds of Wednesday will ease somewhat, but will still be brisk, in the 15-25 mph range.
As we head into the weekend, one more storm front will try to push through Friday afternoon, but while the mountains could see some minor accumulations (and travelers should be ready for some sloppy roads), the valleys should be shadowed out from most if not all the rain or snow.
So much attention has been given to the El Niño this winter that another very significant ocean temperature profile has been largely ignored… “The Blob.” And while El Niño has probably peaked, it is still a significant presence in the equatorial Pacific. But “The Blob” appears to have reached its end. I’ll explain more tomorrow.
February 16, 2016
Batten Down the Hatches
Strong winds associated with a cold front have kicked off a High Wind Warning for western Nevada, in effect throughout the day Wednesday. Those winds will create an initial rain shadow for the valleys, but late in the day as the winds ease a bit we could see some rain reach the Reno area. As the front moves through Wednesday night snow levels will fall from 7,500’ all the way down to near the valley floors, although all the heat left over from our recent warm temperatures should limit valley accumulations. High temperatures in the low 60s will crash down to the upper 40s on Thursday.
For the mountains, a Winter Storm Warning will go into effect Wednesday evening, with the heaviest precipitation expected to occur overnight. Possible accumulations are in the one to two foot range above 7,000’, with significantly less at lake level.
By Friday, the storm system should be out of the area, and it looks like things will warm up and dry out in time for the weekend, with valley temperatures approaching 60 degrees by Sunday.
February 15, 2016
Winter Weather to Return
We have one more day of sunny and warm conditions before winter decides to make a comeback. Tuesday should come in with mostly sunny skies and near record high temperatures. But the ridge of high pressure begins to break down on Wednesday, and a reasonably good sized winter storm will push through the region. In the valley, the winds will be the most noticeable initial effect, and a Valley wind advisory kicks in throughout the day on Wednesday. By Wednesday afternoon rain is likely to fall in the mountains with initially high snow levels. Snow levels should fall below the passes in the late afternoon and will continue to fall to close to valley floor elevations by Thursday morning. A Winter Storm Watch is in effect for the mountains from 7 pm Wednesday night until noon on Thursday. Snowfall amounts will vary greatly depending on elevation, but the ridge tops could receive well over a foot of snow, while the lake Tahoe area could see several inches. It’s unlikely that the lowest valleys will receive any accumulations, however the Thursday morning commute could get a little dicey in the North Valley’s and in the foothills.
February 12, 2016
Dry Weekend, Storms Return Next…and Jet Stream Questions.
The weather will remain dry and mild, if not cloudless, through the President’s Day weekend before a storm system finally returns in the middle of next week. For Saturday, morning clouds will likely clear out by the afternoon and temperatures will top out in the low 60s, staying there through Tuesday. Wednesday, I am becoming more confident that a moderate winter storm will push through the region bringing rain and snow to the mountains, which should turn to all snow in the mountains by Thursday, although it’s unlikely snow levels will drop enough to cause any accumulations in the valleys.
Joe wondered: “Is there a corresponding jet stream in the southern hemisphere? Do large land areas that are not present in the southern hemisphere affect the jet stream?”
Yes, there are corresponding jet streams in the southern hemisphere, and they act much like the ones up here do. They even flow the same way (generally west to east.)
As for large land areas’ effects on the jet stream, it’s kind of hard to answer that in real simple terms, because if you really want to get down to brass tax, anything anywhere that touches air can have some effect on the chaotic system that is the atmosphere. “If a butterfly in Tokyo flaps its wings, it can cause rain a week later in New York” is an old adage that at least holds some truth in theory, if not being absolutely provable. Having said that, landmasses do have a limited effect on jet streams.
Land receives and releases heat from the sun more rapidly than the oceans do, and therefore the vertical convective air currents (called Hadley, Ferrel and Polar Cells) which on a large scale help form somewhat stable weather patterns will have differing strengths over the oceans versus over continents. If your eyes are beginning to glaze over by all of this, suffice it to say that the continents can have an effect on the positioning of large scale persistent weather patterns, which also help determine the strength and position of the jet streams. But in terms of direct interaction between land and jet streams, there’s very little. Since the jet stream is usually found above 25,000’ of elevation, you’d have to get to the Himalayas before the land has any real touch on the jet.
And even though we often talk of the jet stream as a single entity, there are really four of them typically circling the globe. There’s a polar and a sub-tropical jet stream in each hemisphere, each generally following a sinuous path from the west to the east. The polar jets are lower in the atmosphere (generally 25-35,000’ altitude vs. 35-60,000’ for sub-tropical jets), and they tend to be stronger in the winter when the contrast of the polar and tropical airmasses is the greatest.
And at times you can get other types of jet streams, including one in the summer that goes the opposite direction (east to west) down in the tropics, and low-level jet streams can affect the strength of winter storms hitting the west coast. That’s one kind of jet stream on which the land does have a large effect.
February 11, 2016
Storms Should Return Next Week…and Pressure Cooker Questions
Conditions will stay dry and quite warm through the President’s Day Weekend, although the ridge of high pressure responsible for the aforementioned will be flat enough to allow variable amounts of cloudiness to pass over the Great Basin. Friday’s high temperatures will approach record levels (mid to upper 60s) and will stay in the 60s throughout the weekend. There is increasing indication that a storm will move through the region next Wednesday and Thursday bringing high snow levels initially, which will drop to near but likely just above the valley floor on Thursday.
As a follow-up to yesterday’s column, Beryl asks: “Maybe you can explain this to me in a way that makes sense… no one else has been able. Pressure cookers rely on high pressure to generate high heat. Also, when you cover a pot of water, it gets to the boiling point faster, right? So… why doesn’t atmospheric pressure act the same way?”
Actually, it does. A pressure cooker is basically a closed pot that allows the pressure to build up inside as the water tries to boil. A pressure release valve on the top controls how much pressure builds (it’s meant to cook things… not blow up kitchens.) As pressure rises, the boiling point of water rises… up to about 250 degrees instead of 212 degrees for water boiling at standard pressure. At higher altitudes, just the opposite happens. With lower pressures, water boils at a lower temperature, cooking at a slower rate.
As for putting a lid on a pot to speed up boiling, that’s a little different. Unless the lid is sealed to the pot (not a good idea), its presence only serves to keep the heat inside the pot, which shortens the time needs to get it up to a boil.
February 10, 2016
Record Warmth? And Cooking at Elevation (Pt. 2)
Very warm and dry conditions with variable cloudiness will continue through the weekend, with a record high temperature on Friday a possibility. Highs will climb into the mid-60s Thursday and could reach 68 by Friday, topping the old record by a degree. Very slight cooling comes in over the weekend, but that will only drop the highs into the lower 60s. Conditions stay dry into next week, but a couple of storm fronts seem ready to move through the region starting Wednesday.
Yesterday I mentioned that you may have to make some adjustments in cooking at elevation. At sea level, water boils when its temperature reaches 212 degrees F. But up here at about 5,000 feet elevation, water will boil at 203 degrees. That’s because there’s about 20% less air pressure up here. With less air pressure, liquid water molecules find it easier to break away and become water vapor molecules, taking less heat to make water boil.
But if you’re baking a cake and not boiling bratwurst, why should a lower boiling temperature make a difference? That’s where chemistry comes in. Cakes, muffins and the like all have water as a part of their makeup.
Since one of the ingredients in cakes is water, that lowered boiling temperature will affect the cake’s cooking process. But there’s more to it than just that. The lower pressure will also affect yeast… in particular how fast the fermentation process causes the gas it emits to expand, which in turn affects how fast breads and cakes rise. With lower pressure, the gas bubbles expand quicker, which means that you can use less leavening agent (yeast) when baking at higher elevations.
February 9, 2016
Very Warm…And High Altitude Cooking (Pt. 1)
While variable amounts of cloudiness will break over the strong high pressure ridge that is planted over the west coast, said ridge will also result in dry conditions and very warm temperatures throughout the rest of the week. Highs will climb into the mid-60s Wednesday and stay there until the weekend, where they will fall only slightly into the low 60s. At this point, the next chance of precipitation doesn’t come along until mid to late next week.
Joseph Kielbasa (a very appropriate name as you’ll see) sent me a delightful packet in the mail some time ago. In it he said that while visiting family in New Mexico over the holidays, his mom showed his wife some recipes for Southwestern cooking. But it wasn’t the culinary nature of the books that caught his interest, but rather the first several pages that contained information about cooking at high altitudes.
For the uninitiated, you really do have to change some of your cooking habits here as compared to, say, San Francisco. And no, that doesn’t mean you need less tofu here. But you may need to adjust the thermostat… and ingredient list. It all has to do with air pressure… and water.
February 8, 2016
Dry Stretch…But Don’t Give Up on the Winter
A large ridge of high pressure (we haven’t had a lot of those this winter) will settle in over the west coast for the next week, giving us very warm, though not record setting temperatures. Sunny skies and high temperatures in the low 60s Tuesday will give way to a few clouds midweek, but temperatures will stay up in the 60s into the weekend, with lows near the freezing mark. Winds will generally light throughout the week.
While a large ridge of high pressure isn’t the greatest news when it comes to pulling ourselves out of the drought, it is by no means unusual, or a sign that our wetter than average winter has run its course. Even in the wettest winters, there is almost always a dry spell somewhere in the middle. And looking ahead to some of the longer range computer models (keeping in mind those can change as we get closer), there is some indication that as we approach the latter part of February we could be moving back into an active weather pattern.
February 5, 2016
Dry Outlook…And The Challenges of Mountain Forecasting (Pt. 2)
After some overnight and morning cloudiness, the skies should clear off as Saturday progresses, and we will be looking at a mostly sunny Super Bowl weekend. Temperatures will also warm up into the low 50s through Sunday, and steadily climb into the low 60s by Tuesday or Wednesday. Even though a few clouds come back into the forecast picture mid-week, it looks to stay dry for the foreseeable future.
So why is this area so tough to forecast? Let’s go back to the topography that I mentioned yesterday. Those same topographic forces that can produce air movement upward (wind flowing up the windward side of the mountains, creating rain and snow) are reversed when the air is flowing down our (the leeward) side of the mountains. Air forced downward is warmed and “un-saturated”, suppressing precipitation. It doesn’t really lose moisture, but warmer air will evaporate clouds, and without clouds, you don’t get precipitation.
When you have dynamics that are producing precipitation on the other side of the mountains, it is tough to know whether the suppressing effect of leeward (downward) flow will stop the precipitation or not. So I have to decide if the rain in Sacramento will hold together all the way over here, or if it will disappear on the way down the mountains.
It’s a classic description of the “rain shadow” that you might have heard me whine about from time to time. It’s been the source of a lot of embarrassment in the past.
And I’m sure it will continue to do so in the future.
February 4, 2016
Super-Weekend…And The Challenges of Mountain Forecasting (Pt. 2)
A fairly strong ridge of high pressure will keep us dry for the next several days, and temperatures that have been lagging behind seasonal averages will climb above the norm once we get into the weekend. A few clouds will pass over us Friday afternoon ahead of a weakening frontal band, but those should move out by the weekend leaving Saturday and Sunday mostly sunny. Highs Friday will be in the mid-40s and will climb into the 50s through Tuesday and may hit the 60s by mid-week.
So why is it so challenging forecasting near mountains? In a nutshell, the mountains make it tough to forecast (at least on this side of the mountains) because they change the vertical motion of the air. In order to get rain and/or snow, air has to be forced upwards, either by topography (called orographic lift), or by dynamics in the atmosphere, such as a cold front, upper-level divergence, or lower level convergence (or a combination of any or all), just to name a few. The reason it has to do this is the air has to cool enough so that the water vapor it is will become saturated and condense into clouds. I’ve written other columns on why air moving upward gets colder, so I would just ask that you take my word on that for now. More tomorrow.
February 3, 2016
Dry Forecast…And What Makes This Area So Hard to Predict the Weather? (Pt. 1)
It looks like we are entering an extended period of drier and warmer conditions. A ridge of high pressure will build in after a few Wednesday night snow showers. There will be enough residual moisture around for a couple of days to bring variable amounts of cloudiness across the region before clearing out over the weekend. Temperatures will also gradually rise from the mid-40s Thursday into the 50s by the weekend.
A daughter asked her father to help her completing her science research project. As all good dads do when their kids want help with their homework, he dropped everything, prepared to show his little girl that dad knows everything, and then called me for the answer: “What is it about the Sierra that makes predicting weather so challenging? Any advice on what she needs to look up?”
I really didn’t want to spoil the fun of father and daughter doing a joint research project together and just tell them the answer, so I considered just directing them to a couple of good meteorology websites. But then I caved, and just gave them the answer. I’ll share it with you tomorrow.
February 2, 2016
Drier Weather Ahead…And Good News for Lake Tahoe
We have one more round of some light scattered showers on Wednesday before we go into a prolonged dry period. A weak low pressure center will push a frontal band through the region Wednesday afternoon, giving us in the valley a slight chance of rain or snow showers in the afternoon. Temperatures will warm slightly into the low 40s. After the front passes through Thursday morning, a ridge of high pressure will build across the west coast, drying us out for the foreseeable future. Some residual cloudiness will stay through the work week, but should clear out by Sunday finishing the week on a sunny note. Look for high temperatures to climb into the low 50s by Saturday.
With the level of Lake Tahoe now less than a foot beneath its natural rim, it is still more than premature to say the drought is over. But with a healthier than average snowpack in the Tahoe basin (136% of average for this time of year at last check), there should be enough runoff in the spring to at least bring the lake back up above the rim. In an average year, the lake comes up 15 inches, and barring the taps turning off the rest of the winter, we should do even better than that this spring.
February 1, 2016
More Snow?…And The Good News For Lake Tahoe
While we still have a chance to get a few showers here and there, this should prove to be a much less active week of weather than the preceding several we’ve experienced. Northerly flow coming down the backside of the departing low pressure system will keep our temperatures on the cold side Tuesday (valley highs in the mid to low-30s) and could allow a couple of weak disturbances to drop down Tuesday and late Wednesday, which could spawn a few snow showers here and there, but as we head into the weekend, the skies should clear out and the temperatures will gradually rebound into the low 50s. With the snow on the ground that we have, overnight low temperatures will bottom out in the mid to low teens Tuesday and rise to the 20s by midweek.
It goes without saying that all the storms we’ve gotten is good news for our water situation. To put it into perspective, just this weekend, Lake Tahoe rose two inches. Now while that may not seem like much, it equates to about 25,000 acre-feet of water, and brings the water level to less than a foot from Tahoe’s natural rim. Tomorrow, I’ll tell you why that’s such good news.
January 29, 2016
Wild Weekend…and Looking Back to a Record Low Pressure
It is shaping up to be a very active weather weekend. As colder air moves in overnight Friday into Saturday, snow levels will drop to near the valley floor by Saturday morning and then should fall all the way to the floor by Saturday afternoon. As the colder air comes in, the heaviest moisture should move out of the region, but there could still be scattered snow in Reno through the afternoon.
The wild card in the weather story comes in on Sunday. A colder winter storm comes on the coast, and depending on its track, could result in nominal to significant snow in the Reno area. Heaviest snow should be south of Reno, but as the low passes by south of us, we might be able to get some wrap around snow reminiscent of a Tonopah Low. Because of this, a Winter Storm Watch has been posted for the Reno area for Sunday. Stay tuned.
Six years ago (January 14, 2010) we set an all-time record for the lowest barometric pressure here in Reno of 28.92”. Interestingly enough, it wasn’t accompanied by super-strong winds like we’ve had lately (although it was quite windy a day or two prior to the record being set.) The low pressure was caused by a very deep and strong low pressure center which raised havoc in the west (although we missed out on some of the best precipitation here in Reno.)
High winds aren’t necessarily connected to low pressure per se, but rather to areas in which there is a strong change (gradient) in pressure. When we were at the bottom of the barometer reading, we were close to the center of the surface low, and there’s not that much gradient in the center. Our strongest winds generally occur when the rate of change in pressure is the highest.
If you recall, the stronger winds came before the pressure bottomed out. You can relate it to a hurricane. The lowest pressure is in the eye, but the winds are almost non-existent there. They are much stronger away from the center where the pressure gradient is the greatest.
High winds can also be associated with high pressure, but as is the case mentioned earlier, they are strongest when the pressure is climbing fast, not when it has reached its peak
January 28, 2016
A Wild, Windy and Wet Weekend
It will likely be very challenging getting across the mountains this weekend. An Atmospheric River storm will hit the region Friday with potential heavy rain and snow above 8,500’, and high winds that could gust to over 60 mph in the valley. Valley rainfall will vary depending on how close you are to the mountains, with the west side receiving significantly more than the eastern side. Snow levels will begin to drop Friday night into Saturday, falling to about 6,000’ by Saturday morning, and then falling farther to the valley floors by late Saturday. The timing of the snow level drops is still a bit uncertain, so amounts that we might get here in the valley is equally uncertain (a couple of inches is possible by Sunday), but the mountains should get significant rain and then snow through Sunday. Total amounts in the highest elevations should be measured in feet as opposed to inches, and depending on the timing of the colder air, Lake Tahoe could get a foot or more before it is all said and done. The high winds will also combine to make travel across the passes very tough Saturday into Sunday, and a mountain Winter Storm Warning has been posted starting late Friday as a result.
January 27, 2016
Warm and Wet to Cold and Snowy…And Why Atmospheric Rivers are So Wet (Pt. 3)
A very warm Thursday will mark the end of the respite in our wintry pattern, as a series of strong storms begin Friday. Friday, an Atmospheric River pattern sets up with very wet conditions in the mountains and high snow levels (about 8,000’), and there should be enough dynamics to spill over into the valleys. High winds will cause some shadowing though. A cold front moves through the region Saturday morning which should drop the snow levels below Lake Tahoe level, and nearly to the valley floor. Colder air moves in Sunday bringing snow showers to the valley floors. Temperatures steadily fall from the 60s Friday to the 40s Saturday and the 30s Sunday through Tuesday.
Atmospheric Rivers can produce an awful lot of precipitation not only because they originate from the tropics, but also due to their orientation. They form long, straight “rivers” of precipitation that flow along their orientation, which often doesn’t move very quickly. Most front driven storms act like an oscillating sprinkler, which may get you wet briefly, but the band of showers moves past pretty quickly. An Atmospheric River acts like a hose pointed at you continually, dousing you until it is redirected some place else.
January 26, 2016
Wet Weekend…And Why Are Atmospheric Rivers So Wet? (Pt. 2)
We still have another couple of days of dry but cloudy conditions across the region before the ridge of high pressure breaks down and allows a wet and aggressive storm to come through over the weekend. Temperatures will warm to the mid-50s Wednesday and will climb into the low 60s by Friday, when the first wave of precipitation will likely start. The Friday event is shaping up to be a moderate strength Atmospheric River event, with high snow levels (8,000’+), and most of the computer models seem to be in agreement with that picture. That would result in significant rain, especially in the mountains below the passes.
The weekend gets a little less certain, but colder air does move into the region, dropping snow levels to below Lake Tahoe Saturday and possibly all the way to the valley floor by Sunday.
So what makes an Atmospheric River (AR) so wet? There are two main factors. First, the moisture source is usually straight out of the tropics, which of course is a very wet air mass. But even more important is the configuration of the precipitation plume. I’ll expound on this tomorrow.
January 25, 2016
Dry Week…But Could A Pineapple Express Be on the Way?
We have a break in the action for the next several days as a ridge of high pressure settles in over the west coast. Mostly sunny skies will cover the region for most of Tuesday, although variable amounts of cloudiness will likely work their way over the ridge as the week progresses. Temperatures will rise from the upper 40s Tuesday and could reach the lower 60s by Friday as the next storm system works its way here, and this upcoming weekend has a chance of being pretty wet.
Speaking of this next storm system, it’s starting to shape up to have some characteristics of an atmospheric river (what we used to call a Pineapple Express.) If you are looking for a very wet pattern, it doesn’t get much better than an AR. An AR can take a deep plume of moisture, usually from the tropics (hence the Pineapple moniker) and transport it on a straight jet stream straight at the west coast, and are responsible for the largest precipitation events in our neck of the woods. Tomorrow, I’ll tell you more about ARs and why they can be so wet.
January 22, 2016
One More Storm…And When is the Latest Sunrise?
A moderate strength winter storm will roll through the region for the first half of the weekend, kicking up some strong winds and bringing a mixture of rain and snow. The second of two storm fronts will move into western Nevada Saturday morning, dropping snow levels to near the valley floor, although no significant valley accumulations are expected. High temperatures will drop to the 40s and will remain there through the weekend.
The mountains are under a Winter Weather Advisory through Saturday afternoon, with 2-7” of snow possible depending on elevation on the eastern side of the crest, and heavier amounts possible once you get over to west of the passes. Scattered showers will continue into Sunday morning after which things should dry out and remain so well into next week.
Pete had the following comment: “I know Dec 20 or 21 is the shortest day of the year, but what is the date of the latest sunrise? And while we are at it how about the earliest sunset?”
One might think that the latest sunrise and the earliest sunset would be on the Winter Solstice (Dec 21 usually), but because of the eccentricity of the earth’s orbit that isn’t the case. The sunrises keep getting later for about two weeks after the solstice, and they max out about the 5th of January, just before 7:20 local time. The earliest sunset is on the other side of the solstice, on the 8th or 9th of December (depending on the year), at 4:36 local time. The combination of the two still makes the solstice the shortest day of the year.
January 21, 2016
Another Round…And How You Get Freezing Rain (Pt. 2)
We have a two-punch storm system coming in over the weekend that will bring another round of mainly rain in the valley (although a few snow showers Saturday is possible) and mountain snow (although a few mountain rain showers are possible Friday.) The first wave arrives Friday morning with snow levels that might start at the Lake elevation, but will likely climb to nearly 7,000’ by the afternoon. In Reno, strong southwest winds will keep us shadowed out for the most part, but some spillover showers could occur on the west side of the valley. The second and colder impulse comes through late Friday night, and snow levels will drop to near the valley floors on Saturday, although little to no valley accumulation is expected. Highs in the 50s Friday will drop to the 40s Saturday and Sunday before rebounding to the 50s with a drier outlook next week.
So how do you get freezing rain? In general (and perhaps obviously) you need to have warm air aloft on top of cold air at the surface… along with (again obviously) some rain. This can occur a couple of different ways. A warm front will always shove warm air up over colder surface air, and is a relatively common way to get freezing rain in the central plains states. Here in Nevada, these cold air inversions that we have been having can also trap enough cold air in the valleys to create freezing rain, although it is fairly rare.
January 20, 2016
Weekend Storms…And The Difference between Sleet and Freezing Rain (Pt. 1)
We have another mild an uneventful day coming up Thursday before the storm wagon gets rolling again. A low pressure center will slowly move in as we head into the weekend, bringing another chance of valley rain and mountain snow. For Thursday clouds out ahead of the low will cover western Nevada, but temperatures will stay mild (low-mid 50s) and we should stay dry. On Friday, a weak system splits off of the main low bringing a chance of valley rain and high elevation snow. On Saturday, the main part of the storm arrives, which will increase the chance of valley precipitation to the likely level, and will drop snow levels close to the valley floor, cooling us off to the 40s. Things then dry out Sunday.
Many have asked me what the difference between freezing rain and sleet is. Sleet is basically snow that starts to melt on the way down, and falls as a mix of rain and snow. Freezing rain is precipitation that has completely melted into rain on the way down, and then falls into cold air at the surface that is below freezing. This rain usually freezes rapidly as it hits the ground, and is perhaps the most dangerous winter weather pattern. How do you get it? I’ll tell you tomorrow.
January 19, 2016
Short Break…and Then Back At It
We have a bit of a break in the action coming our way, with the next storm system slated to move through on Friday and Saturday. For the short term, a mild ridge of high pressure will bump the next Pacific system to our north. We’ll start out with partly cloudy skies Wednesday, and then catch a little more cloudiness in the afternoon as the southern edge of a cold front brushes by.
One other possibility to consider is a chance of local freezing fog, especially in the area around Truckee, but we could potentially see some in the valleys. High temperatures will stay in the 50s through Friday.
Benign clouds will increase Thursday, but it will be Friday before the next storm system moves through. This will be a colder storm with snow levels that will probably start somewhere around Lake Tahoe, but could drop to near the valley floors by Saturday. I don’t expect any valley accumulations at this point, but once again travel over the passes could get very tough as we head into the weekend.
January 18, 2016
The overall storm pattern remains quite active, with the next moving through the region on Tuesday and the next arriving on Friday. These storm systems will be a bit warmer than many that we have seen so far this season. By early Tuesday morning, the onset of the storm will drop rain below 5,500’, but those snow levels will likely rise to about 6,500’ (just above Lake Tahoe itself). The winds associated with this storm will be quite strong, gusting as high as 50 mph in the wind-prone valley locations, and topping 100 mph on the ridge tops, and Wind Advisories have been posted for western Nevada and the Sierra. Because of the strong winds, there will be considerable rain shadowing occurring, so rainfall amounts in the valley will be limited, and will drop off very quickly as you go east from the mountains.
There will be a bit of a break Wednesday and Thursday with mild temperatures (in the 50s) before the next storm arrives, bringing a good chance of rain which might turn to snow Friday into Saturday.
January 12, 2016
One Right After Another…
There really doesn’t seem to be much of a break in the stormy pattern which is bringing in an almost continuous series of storms off the ocean. As has been the case lately, none of the storms individually seems to be of more than moderate strength, but it should add up to a pretty hefty amount of mainly mountain snow with occasional valley rain. On Wednesday the next storm hits with enough mountain snow forecast to kick off a Winter Weather Advisory for the Sierra (2-8” are possible depending on elevation and location.) For the valley, it looks like this one will be warm enough so that if we do get anything (and there will be a significant drop in precipitation in the valleys due to the rain shadow) it will likely be rain until you get quite a ways up into the foothills. By Thursday, there will be a brief break before the next storm arrives Friday into Saturday. And a chance of showers (mainly valley rain and mountain snow) will continue well into the next week.
January 11, 2016
Active Pattern Continues
Once again, we are in a fairly active storm pattern this week, although none of the systems that will come through the region will be real barn-burners. Clouds will increase Tuesday ahead of the next winter storm that should arrive Wednesday early. The Storm itself will weaken as it comes across California, but the added lift provided by the mountains should result in a few inches of snow at Lake Tahoe with as much as a foot in the prime ridgetop locations. This storm is warmer than the last several that we’ve had, and snow levels could start out just above Lake Tahoe level initially before dropping to near the valley floors later in the day. Because of the warmer nature of the system, I don’t expect to see any lower valley accumulations, but enough is expected in the mountains so that a Winter Weather Advisory has been issued up there from 4 am to 6 pm Wednesday. Isolated to scattered showers will continue Thursday and Friday before a somewhat stronger system tries to move through over the weekend.
January 8, 2016
Here Comes Another Storm…And Dispelling More El Niño Myths (Pt. 2)
Yet another in a long line of winter storms will move through the region on Saturday, adding several inches of snow to the mountains, but only likely to produce scattered rain or snow in the western Nevada valleys due to shadowing. The main precipitation band will move through fairly quickly Saturday leaving a mostly dry Sunday before the next weak storm tries to move through on Monday. The long-term outlook seems to keep us in a fairly active pattern of weak to moderate storms coming through on an every-other day or so frequency.
Yesterday, Jim wondered if a typical El Niño would increase our chances of flooding. While flooding might seem logical, let me dispel a couple of misconceptions about El Niño. While flooding can be an issue with El Niño patterns in southern California, El Niños are not any more likely to cause flooding here in northern Nevada than non El Niño years. The biggest floods we’ve had here in the Reno area weren’t associated with El Niño, but rather atmospheric rivers, which are not any more prevalent in El Niños (and in fact may occur more often in La Niñas.)
Some have written me asking if it will really do us any good from a water standpoint, because of a concern that El Niños have so much higher snow levels, and wouldn’t that just reduce the amount of snow, especially in the lower elevations? The storms we are seeing this week do fit the “El Niño signature,” although even that is a pretty loosely defined criterion. And an El Niño doesn’t necessarily demand a high snow level, although on average they do tend to be a bit higher. But there is a lot of buffer to snow levels, and even if the slow levels are a bit higher, the additional moisture more than makes up for it. Of course lately our snow levels have been pretty low with most of the valley precipitation in the form of snow.
Right now, we are already well ahead of a “normal” snowpack for this time of year, with our 4 basins ranging between 110% (Truckee River Basin) and 140% (Tahoe Basin) of average for this time of year, and that doesn’t take into account what they got yesterday. There really hasn’t been such a thing as bad precipitation lately.
January 7, 2016
A Break, But Still an Active Pattern…And Dispelling More El Niño Myths (Pt. 1)
While we will have a bit of a break in the action on Friday, we are still in a reasonable active pattern that looks like will stick around for the next week at least. After variable amounts of cloudiness on Friday with highs in the upper 30s, the next storm system moves onshore late Friday night into Saturday. As has been the case with the other storms this week, this next one isn’t real strong in itself, but could result in several inches of additional snow for the mountains, and perhaps minor valley accumulations. After another break Sunday additional systems are lined up for next week.
Jim noticed that I recently mentioned that these latest storms have more of an archetypal “El Niño” signature, and he wondered: “Does such a system mean that we will see the jet stream drop lower towards the Hawaiian Islands and the systems are warmer that leads toward flooding throughout California and Northern Nevada?” It’s understandable that Jim would assume that anything associated with El Niño would naturally result in something disastrous, since that seems to be all you hear in the media. But tomorrow I’ll try and dispel some of those misconceptions.