Wasatch Weather Weenies

Measuring precipitation rates during winter storms is a remarkably difficult problem.  The basic problem is that the wind blows, and this affects the collection efficiency of traditional rain gauges, such as the one below. The problem is that as the wind interacts with the gauge, it alters the flow in a way that some snowflakes are carried over the gauge rather than falling into it. Source: Rasmussen et al. (2012) The traditional way to deal with this problem is to put some sort of a shield around the gauge to reduce the airflow, such as surrounds the gauge in the picture above.  More extreme measures involve putting additional snow fences around the gauge, which is especially important in open windy areas as found, for example, across much of the high plains.   Source: Rasmussen et al. (2011) Even with these measures, traditional rain gauges still suffer from what is known as undercatch.   They typically measure liquid-equivalent precipitat...

We are in for a wild ride today with a little bit of everything thrown at us thanks to the passage of a spring cold front. In the prefrontal environment this morning (about 8 am), the Salt Lake Valley and Wasatch Mountains are seeing strong south winds with dust. A partially obscured Wasatch Range due to blowing dust At 8 am, temperatures ahead of the front were very mild with a 62ºF reading at the Salt Lake City airport, 40ºF at the base of Alta, and 32ºF at Alta–Collins. Things are going to change very quickly, however with the passage of the cold front, which is just upstream of Salt Lake City as I write this.  The temperature at the north end of the Great Salt Lake, for instance, is only 38ºF. Source: MesoWest Further, radar shows precipitation is moving in.  Some of this is evaporating before it reaches the valley floors, but valley showers and mountain snow will eventually be on the increase. Source: NCAR/RAL We may see some snow at bench level late ...

Yup, the bonus season is most definitely here.   I did a short tour into a typically popular area of the Wasatch backcountry this morning and didn't see a soul.  I even had to break trail (gasp), not that it required much effort.  You could find every kind of condition imaginable out there.  I had everything from decent powder to dust-on-crust to wind board to spring mank, and that was in just one 2000 vertical foot run.  Thanks to the high angle sun and a bit of rime on the aspens, views were quite nice If you want to become a better forecaster, going back and evaluating your predictions is essential.  In this event, Alta-Collins ended up with 15 inches of snow, which is at the bottom threshold of the 15–24 inches I went for on Wednesday .  At that time, the 12-km NAM called for 1.08 inches of water and we ended up with 1.27", which yields a mean water content of 8.5%.  There are two sources of error in snowfall forecasts.  The first...

Today looks to be one of those classic spring days that epitomizes the phrase, "if you don't like the weather, wait five minutes." A cold and unsettled airmass has settled over northern Utah this morning with nearly everyone experiencing scattered showers. The morning sounding shows a weak cold pool at the surface, but otherwise very steep, conditionally unstable lapse rates aloft.  A little surface heating should help further destabilize this sounding and keep the shower activity going during the day. The models suggest some warming in the upper atmosphere during the day today, but with abundant moisture and steep lapse rates at low levels, I think we're going to see some thunderstorm activity anyway.  Snow levels in the stronger cells may drop to the valley floor.  I'm still a bit surprised we haven't seen a few more flakes on the benches so far, but temperatures are about 2ºC warmer than progged by the models yesterday, so the snow level has bee...

It's a remarkable day if you are a meteorologist.  We'll talk first about the pending storm for the Wasatch. A weak surface cold front pushed into northern Utah this morning without much fanfare.  However, precipitation will eventually move in this morning and we will likely see periods of mountain snow in the cold (compared to what we've seen the past few weeks), unstable westerly and northwesterly flow through late Thursday night or Friday morning.  The system will eventually be cold enough that at times the snow level may push to the valley floor.  If you see some white, don't be surprised. Amongst the products that we use to forecast the weather are time height sections.  They basically provide a series of profiles so that you can see the temporal evolution of the atmosphere at a given point.  It is convention for time to increase to the left in these diagrams. The time-height section from the 0600 UTC NAM for Salt Lake City is below and shows profi...

Over the past couple of years I've been working on the definitive weather and climate book for those seeking deep powder and passionate about snow.  The cover has just been finalized and it is now full steam ahead for release in the fall, just in time for next ski season.   If you enjoy reading this blog, you will love the book.  In addition to revealing the real reasons why Utah has the Greatest Snow on Earth (and debunking the myths), it provides a meteorological guide to weather and snow climates around the world (with insider tips on where to find the best and most reliable powder), presents a historical and present-day account of avalanches and avalanche mitigation efforts in the Wasatch Mountains, and explores the basics of weather forecasting and climate change. Preorder on Amazon coming soon, so stay tuned.  Much thanks to everyone who contributed to the book and to the staffs at Utah State University Press and the University Press of Colorado.

April is around the corner.  The high tomorrow (Tuesday) will probably eclipse 70 at the Salt Lake City airport.  People are biking and golfing in the valley.  The tourists and locals are giving up on ski season. That's fine by me as it means fewer people to share the mountains with when the jet stream returns to Utah later this week with the first wave of moisture pushing in Wednesday morning. Right now things look fairly active on Wednesday and Thursday, with the NAM generating 0.93 inches of water and 15 inches of snow from Wednesday morning to late Thursday in upper Little Cottonwood Canyon. The thing about late March and April storms is that one needs to delicately balance patience and urgency.  You often need to wait until it piles up (that snow on Wednesday will be likely fall on a hard, frozen surface on most aspects, so it will take a lot to bury the bottom), but also need to get out quickly during or immediately following the storm since the sun is m...

Dusty snow on the south facing aspects near Alta, UT Dust deposited in the snowpack by this past week's dust storm is already starting to appear on the snowpack on south facing aspects.   As the surface snow melts, it percolates past the dust, which collects at the snow surface.  This process is particularly rapid on south facing aspects like those in upper Little Cottonwood Canyon, although even north-facing aspects eventually suffer (although for now, the dust on the north-facing aspects is buried).  Further, dust absorbs more solar radiation than pristine snow, so it accelerates the snow melt.  Yup, global warming isn't the only thing affecting the future of snow in Utah.   Although the bulk of our dust comes in intense storms like the one last week, we sometimes have more diffuse events that can be from regional dust sources in the western U.S. or even from Asia.  I think we may have such an event underway today as one could see a dusty tint in t...

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Last Friday we discussed how short-wave troughs can sometimes cause forecast problems in long-range forecasts (see Short-Wave Mischief in the Medium Range Forecast ).  Today we'll discuss how they can serve as flies in the ointment of short-range forecasts (3 days or less). The forecasts from yesterday (Wednesday) morning called for a short-wave trough to skirt us just to the north, with cooler, drier air moving into northern utah on Saturday morning.  Precipitation in northern Utah was very limited, with only a very small are of light precipitation on the north slope of the Uinta Mountains in the NAM. Overnight, however, we see a subtle change in the characteristics of the large-scale forecast with a weak, but still significant extension of the trough extending west-southwestward into northern Nevada.  This leads to more humidity over the state (compare lower left panels) and a band of precipitation over the Uinta Basin. The net impact of such a shift is an ...

Much has been made recently in media reports of the so-called "global warming pause" or "hiatus", a slowdown in the rate of increase of mean global surface temperatures over the past 10–15 years, as can be inferred from the graph below.   Although the causes of this slowdown are still being worked out, when one looks at the Earth's climate system as a whole, it is pretty clear that global warming is continuing unabated. Global warming affects not just the atmosphere, but also the hydrosphere (i.e., the oceans), the cryosphere (i.e., snow and ice), and the lithosphere (the Earth's crust).  The accumulation of energy produced by global warming thus can be expressed not only as a warming of the atmosphere, but also in terms of a warming of the oceans, melting of ice, or warming of the land surface. A nice plot showing this energy accumulation is provided in the IPCC Fifth Assessment Report (AR5). The energy accumulation is dominated by deep and uppe...

Yesterday's strong westerly and northwest winds ushered in the first major blowing dust event of the spring.  Here's a look at the dust accompanying the rather ill-defined cold front pushing into the Salt Lake Valley (courtesy George Wilkerson and Steve Krueger). We will see that dust again later this spring.  It's been deposited now in the mountain snowpack and will rise to the top, along with other impurities, as the snowpack melts.  Because dust is darker than pristine snow, it absorbs more sunlight, and thus it's presence accelerates the snowmelt in the spring.   The dust also degrades air quality.  Note the spike in hourly PM2.5 concentrations to 33.5 ug/m3 yesterday morning.  Ick. Source: Utah Division of Air Quality Although many believe that these dust storms are natural events, they clearly have a strong human-caused component.  The bulk of the evidence suggests that the western U.S. is a far dustier place today than it w...

Although we have had a number of spring-like storms over the past few weeks in terms of warmth, high snow levels, and valley rains, I'll call today's event the first "spring trough" of the season. Short-wave troughs like the one approaching us this morning (see above) are a dime a dozen, but they pack a stronger meteorological punch in spring rather than winter.  The reason for this is surface heating, which is stronger in the spring and creates a less stable lower atmosphere, allowing for stronger coupling with systems aloft.  This is why we see stronger surface cyclones and cold-frontal passages in spring rather than winter.  Further, the strong winds accompanying these systems can frequently lead to dust storms that can lead to poor visibility and air quality in lowland regions and darken the snowpack in mountain regions. Today's system has a lot going for it.  It's a fairly strong short-wave trough with a monsterous 700-mb temperature contrast of 20...

Alf's High Rustler, 16 March 2014 It's a sure sign of spring when sun returns to the steep north-facing terrain of the Wasatch Range, such as Alf's High Rustler above.  For about a 4 month period centered on the winter solstice, the sun is too low in the sky to touch these aspects.  That's not the case anymore. For a (nearly) north facing aspect like upper High Rustler, with a pitch to the cat track of about 35 degrees, the first day of potential sun is about Feb 11th, and that's only at solar noon.  Note that right at the top it is close to 45 degrees, so the first sun there is even later (note how it is in the shade in the photo above, which was taken about 90 minutes prior to solar noon).   Today, March 16th, a north facing aspect needs to have a pitch of about 47 degrees to totally avoid the sun (there are some exceptions, such as when there is even steeper terrain adjacent and to the south).  A run like High Rustler gets sun for a few hours, ena...

As a follower of this blog, you are undoubtably aware of declining forecast skill with increasing lead time.  Extended range forecasts are generally less reliable than long range forecasts.  In extended range forecasts, sometimes the models do pretty well with regards to the big picture, but smaller-scale weather features that are inherently less predictable derail the forecast. Case in point is my blog post from Monday, " Spring Break Guilty Pleasures ," in which I wrote: How about a few days of mountain biking, river running, hiking, canyoneering, or rock climbing in the canyonlands of southern Utah? No problemo. Head south later this week for an extended three day weekend. A huge ridge is building in and by Sunday it is parked over St. George. Oooh, I can feel and see those red, sunburned winter bodies already. That forecast isn't terrible as yes a ridge is building in and I expect to see some sunburns on Monday, but the weather on Saturday doesn't look qu...

The Northern Hemisphere's meteorological winter (Dec–Feb) is now in the bag.  The National Climatic Data Center served up its data for February today, allowing us to take a look at what winter brought the United States and Utah. On a national scale, temperatures were well below average in the upper midwest (aren't winters in Minnesota nasty enough already!) and below average across most of the US east of the Rockies except near the coast where temperatures were near average.  In our part of the world, we ended up near or just above average.  In the valleys of northern Utah, that largely reflects below average temperatures in December, near average in January, and above average in February. Source: NCDC The image below shows the rank of this past winter relative to all 118 years since 1895.  A good swath of the upper midwest observed a top-10 coldest winter.  On the other hand, most of California basked in record warmth.  Flights from Minneapolis to...

Weird white stuff on the U grass this morning Old man winter has returned to the Salt Lake Valley this morning, providing just enough snow to aesthetically coat the grass without wreaking havoc on the commute or, more importantly, my bus route.   Meanwhile, the storm has produced 9 inches as of 7 am at Alta-Collins.  It's another high-density dump overall, but should be right-side-up and ski well.  Enjoy.   Finally, in other news, check out this avalanche that took out the High Campbell chair at Crystal Mountain, Washington.  Whoa.  Source: Crystal Mountain Facebook Page Source: Crystal Mountain Facebook Page I have a lot of good memories from riding that chair.  Looks like a new one will be ordered this summer.  So sad to see the demise of another classic fixed grip double.  At least it went out in style.  

It is spring break this week at the University of Utah and the forecast suggests that students and faculty will have every opportunity to take full advantage of the embarrassment of riches found in Utah. Want powder skiing?  How about a winter storm tonight and tomorrow for the Wasatch Range?  Looks like 6-12 inches for the upper Cottonowoods through 6 PM tomorrow.  Tired of winter?  How about a few days of mountain biking, river running, hiking, canyoneering, or rock climbing in the canyonlands of southern Utah?  No problemo.  Head south later this week for an extended three day weekend.  A huge ridge is building in and by Sunday it is parked over St. George. Oooh, I can feel and see those red, sunburned winter bodies already. Want to party?  Ha ha.  Can't help you there.  

If you think that Little Cottonwood Canyon has the most remarkable microclimate in the Wasatch, think again.  Yeah, it snows a lot in upper Little Cottonwood, but if you want to find the snowiest place in the Wasatch for a given altitude, you need to venture north to the Ogden Valley. Utah's Ogden Valley from the Trapper's Loop Highway In particular, you need to venture to Liberty, UT and up the North Fork of the Ogden River.  Here, at low elevations, you will find ridiculous amounts of snow that has been generated and carried over the formidable terrain near Ben Lomond Peak (the thumbnail below is North Fork Park, discussed below). By nearly all measures, this has been a terrible low-elevation snow year in the Wasatch, yet today you can find good cover and great cross country skiing at 5600–6000 ft at North Fork Park where Ogden Nordic, a chapter of The Utah Nordic Alliance (TUNA), maintains a a marvelous system of trails.   Yeah, it's bee a bad sno...

Those with keen eyes may have noticed a nifty little hook in the cloud pattern over the lake in the previous post. Turns out there was what is known as a mesoscale vortex  over the lake this morning.  You can see it in the loop below.  Note how it drifts southward across the SW corner of the lake. How about a high res MODIS image?  At this time, the center of the hook, which almost forms an eye, was sitting over the far SW corner of the lake. Source: NASA This lake-effect stuff is sure complicated.  I'm not sure if this vortex was lake induced or something in the larger-scale flow that just happened to be passing over the lake.