Wasatch Weather Weenies

As far as snowfall and snowpack in the southwest are concerned, February was a disaster. Below is the percent of average snowpack analysis from February 2nd (when I grabbed it for a blog post) showing very healthy conditions relative to average for that time of year across much of the southwest. Source: NRCS Fast forward to today and you can see that we have failed to keep pace with the climatological buildup of the snowpack in nearly every drainage basin in California, Nevada, Utah, Colorado, Arizona, and New Mexico.  The situation in Arizona and New Mexico (as well as the south Sierra not shown here) was especially disastrous.   Source: NRCS Let's take a look at a few select stations.  At Snowslide Canyon in Arizona (9730 ft), the peak snowpack was achieved in mid January, after which the snowpack has not only lost some ground to climatology, but also in absolute terms, with a slight decrease in total water equivalent.   Source: NRCS If we g...

This weekend I was able to get back into the mountains after a 3 week hiatus.  The transformation during that time was quite dramatic, especially on south-facing aspects. The importance of aspect (i.e., the direction a slope faces) cannot be understated in Utah and for skiers, especially this time of year.  Given a few days of sunny weather, it is often possible to find corn (or sun crust depending on the time of day) and dry powder on adjacent slopes. It was pretty easy to find examples of such stark snow contrasts this weekend.  For example, in the photo below, the snow on the left was corn (technically a stout melt-freeze crust since it was taken this morning after the overnight freeze), whereas the snow on the right was soft, settled, dry snow.  The only difference was aspect.  The slope on the left was southeast facing, the slope on the right northwest facing.   The graphs below show the amount of direct solar radiation on north, west, e...

Desperate times call for desperate measures, so today we talk about the dust-on-crust uncertainty for tomorrow.  The loop below shows a sequence of forecasts for tomorrow afternoon from GFS runs initialized from 0000 UTC on the 25th to 1200 UTC on the 26th (this morning).  Note how the area of precipitation shifts southward into northern Utah, then back north, then southward again, then back north. Basically, this indicates some uncertainty in the track of the storm.  If the northern track verifies, we'll probably see anything from a trace to an inch of snow.  If the southern track verifies, maybe we get 2-3 inches.  For what it is worth, at Alta-Collins the NCAR 3-km ensemble calls for very little precipitation and the NAM is going for an inch, so I'm just hoping the wind doesn't blow too hard to ruin whatever high-north powder remains in the upper elevation backcountry.  

Yes, and no. If you mean situations in which a shallow, persistent (i.e., multiday) cold pool is capped by a layer in which temperature increases in height, then it's pretty much over.  With no snow on the ground, a higher sun, and a longer day than a few weeks ago, shallow cold pools are now readily burned off during the day. That being said, we can still have an elevated inversion, as was the case yesterday afternoon. Source: SPC Under such conditions, however, pollutants are mixed through a layer that extends through a greater depth of the valley and PM2.5 concentrations don't get as high as they do during shallower cold pool events in winter.  Nevertheless, you will see some smog around, so we're not pollution free. Does this then mean that elevated PM2.5 days are over for this winter?  Nada.  We are just moving into the time of year when dust storms occur, and I wouldn't be surprised if we saw some events this spring if the dry conditions continue.

With the weather fairly benign over Utah this week, now is a good time to make a few announcements concerning items that may be of interest to readers. 1. The National Weather Service will be hosting the Internountain West Aviation Weather Safety Workshop at Westminster College from May 6-7.  This looks like a good meeting for pilots.  More info below and at http://weather.gov/riverton/iwaws . 2. The Utah Avalanche Center has launched a new initiative centered on backcountry ethics.  This is a critical issue for safety in the backcountry and above highways (e.g., SR-210 in Little Cottonwood Canyon).  Catch the video and coverage at TGR . 3. After a few weeks of scarcity, the 2nd printing of my book Secrets of the Greatest Snow on Earth has hit the shelves and is now available from Amazon and other retailers.   If you don't have a copy already, buy it now to tide you over through the dog days of summer.

As we near the end of February and the home stretch of the snowpack accumulation season, snowpack water equivalents are running pretty close to average across much of the western U.S. Source: NRCS There is, however, reason to be concerned in the southwest where the snowpack in the mountains of Arizona and much of New Mexico are running below average.  I flew over this area about 10 days ago and was blown away by the lack of snow.  Similarly, the southern Sierra are now running at only 88% of average for the date (left hand value below, right is percent of the April 1st average). Source: California Department of Water Resources And, while one always needs to be cautious with extended-range forecasts, there's really not much being produced by the models over the next 1-2 weeks for the southwest.  Just to underscore that point, below is the 8-14 day precipitation outlook for the first week of March. Source: CPC Oh, where art thou El Nino? I see your warm sea...

Some of you have contacted me concerned about my absence.  Thanks for the concern and for checking in.   My father passed away over President's weekend, so my attention has been elsewhere.  He inspired much of what you read on this blog.  I will write again, but don't have a timetable for a return.  I suspect and hope it will be sooner rather than later.  Until then, take a run for us.  Best, Jim

For the most part, the news during prolonged inversion events is bad, but I did want to share one "silver lining" with regards to the current event, which is the cloud cover and what it is doing to increase mixing in the Salt Lake Valley, especially overnight. The air is still polluted, but these clouds are actually a help rather than a hindrance If the solution to pollution is dilution, then the development of cloud cover over the Salt Lake Valley is an improvement over the cloud-free inversion that we had prior to yesterday.  Let me show you why. Below is a loop of upper-air soundings collected each morning at the Salt Lake City airport over the past week.  These soundings are plotted as a "skew-t" so a line of constant temperature slopes upward to the right.  Note the two-stage evolution of the inversion event.  First, the upper levels warm dramatically while the morning surface temperatures remain relatively steady.  This occurs in the first 5 fram...

Some of you have commented about the large difference between the DAQ sampler at Hawthorne and the observations collected along the Trax line as well as at Neil Armstrong Academy and the University of Utah. For the most part, these sensors have generated pretty similar results for the first few days of the inversion.  PM2.5 at Hawthorne has risen fairly steadily during the period (with some ups and downs) with a range from midnight on the 9th to midnight on the 10th between about 38 and 54 ug/m3.  PM2.5 at Neil Armstrong Academy (sorry for change of scale) was generally close to Hawthorne through midnight on the 10th, with the range from midnight on the 9th to midnight on the 10th of about 39 to 65 ug/m3. Source: MesoWest Source: MesoWest The divergence begins shortly after midnight on the 10th (last night), with NAA going to much higher values.  Similar, other samplers operated by the University of Utah at the University of Utah and along Trax are also repor...

The situation in the Salt Lake Valley continues to deteriorate and is becoming quite serious. Here on campus, we are currently fogged in.  Although depressing, it doesn't look as ugly as the pollution does under clear skies, but don't be fooled. PM2.5 concentrations this morning are sky high.  The University of Utah's Trax-mounted PM2.5 sampler is measuring concentrations this morning in the 85-115 ug/m3 range (maroon filled circles below). I did a quick inspection of the data and found a maximum concentration of 111 ug/m3, which is well into the unhealthy category.   The terrible situation we are in is one of our own doing.  Persistent cold pools (a.k.a., inversions) are naturally occurring phenomenon in the western United States during the winter.  One shouldn't equate inversions with air pollution.  Inversions happen all over the west.  Pollution happens in those areas that experience inversions and where emissions are concentrate...

A comparison of soundings from yesterday morning and this morning shows further strengthening of the inversion over the past 24 hours.  Yesterday morning, the surface temperature was 27ºF (-2.8ºC), with temperatures aloft maxing out at 1.4ºC just below 700 mb (10,000 ft). Source: SPC This morning, the surface temperature is once again 27ºF (-2.8ºC), but temperatures aloft have increased at all levels up to about 650 mb, with a maximum of 3.6ºC at 773 mb (8000 ft). Source: SPC Above the valley floor, the freezing level isn't hit until just over 12,000 feet.  You'll find some below freezing air in cold mountain spots this morning, but with the exception of shady north-facing spots, temperatures throughout the Wasatch Range will be above freezing today. Air quality in the Salt Lake Valley continues to deteriorate.  Observations from DAQ sensors and from Trax-mounted sensors operated by the University of Utah are generally between 35 and 60 ug/m3, which is in th...

After a run of active weather and regular powder refills from about mid December through early February, the wheels have come off our winter. We are now fully in the grips of a monster upper-level ridge that will keep the mountains dry and the valley inverted.  On the positive side, that means warm, sunny days in the mountains.  On the negative side, we are staring directly down the barrel of what will be a very poor air quality episode. Meteorologists use a diagram known as a Skew-T to examine upper-air soundings collected by weather balloons.  In these charts, lines of constant temperature are "skewed" (blue dotted lines below).  Yesterday morning's sounding showed a shallow inversion at low levels.  The surface temperature was 26ºF -3.3ºC and the temperature at the top of the inversion near 800 mb was about 0ºC.  Above this level, at 700-mb near the crest of the Wasatch Range, the temperature was about -4ºC. Source: SPC The big change overnigh...

Smog in the Salt Lake Valley this afternoon as viewed from the Mt. Olympus Wilderness.  Antelope Island sticking up in the distance. It's time to get real about the air quality this week.  The system that passed by yesterday, and the strong crest-level winds today, have done essentially nothing to stir up the air in the Salt Lake Valley.  We are now facing a situation where the air quality is already poor as a remarkably strong upper-level ridge builds over northern Utah.  With snow on the ground, this is essentially a worst-case scenario for air quality in February and it needs to be treated as such. How bad is the air qualty?  Well if you wanted to know this afternoon and had to rely on the Utah Division of Air Qualty, the answer is unclear.  Here's what I got when I tried to go to their web site this afternoon.  This is simply unacceptable, because the air quality is indeed poor this afternoon.  We know because the University of U...

It's a spectacular day in the mountains today.  One that will surely infect some with spring fever.  Visibility was outstanding and I was quite happy to share the day with my son. We really experienced three seasons today.  The first season was on south-facing aspects where the February sun was causing  dendritic destruction and made it feel like spring.  I was glad we did our south-facing climb early in the morning as it was like a microwave by mid day. The second season was on other aspects where you could find some nice, settled, mid-winter powder.  This was essentially my son's first taste of pure, unadulterated, Wasatch backcountry powder.  No doubt he'll be back for more. Of course, I also taught him some other critical skills required for backcountry skiing. The third season we experienced today was after we returned to the smog of the Salt Lake Valley.  Yes, inversion season is still here. Unfortunately, the system...

I am swamped today with the demands of my day job.  I wish to take a moment to highlight two important items. First, a monster ridge will be in full force next week. We are already in moderate air quality and it's still unclear if we're going to get much relief from the system that will be passing to our north tomorrow.  A poor air quality episode is likely next week.  Now is the time to reduce trips and cut emissions. Second, the Mountain Accord is doing a transportation survey for the Cottonwood Canyons.  Put in your $0.02 at http://mountainaccord.com/mountain-accord-transportation-survey/.

After yesterday's bummer of a trough passage, which produced all of one inch at Alta-Collins, I confess that I was in quite a pessimistic mood when I went to bed last night.  Thus, it was a pleasant surprise to wake up to a fresh coat of some of Mother Nature's finest dendrites. The real surprise, however, was in the mountains.  The Little Cottonwood snowmaking machine was really cranking last night with Alta-Collins picking up 11 inches of cold smoke.  That appears to be quite a bit more than fell elsewhere in the Wasatch, as well as that predicted by the models and by operational forecasts.  The National Weather Service Little Cottonwood forecast issued yesterday afternoon called for a 20% chance of a trace and an 80% chance of 1-3". Source: NWS And just to show I'm not picking on them, I last did a blog post on Wednesday and while it examined the high-amplitude ridge that will be building over us the next few days, I did mention that I expected 2-4" ...