Wasatch Weather Weenies

There's no doubt that the top 2023 weather story in Utah was the record setting snowfall and snowpack.   Technically, this is a story that began with the first mountain snowstorms in October 2022.  Below was the scene on the "Collins Glacier" at Alta on October 29th, 2022, when the snow depth at the Collins observing site was already a solid 23 inches. Early season powder skiing was then had into early November.  By November 11, when the photo below was taken, we had already crested a 60 inch snow depth at Collins, my mark for the start of "good early season conditions."  It's hard to believe now, but the spigot actually shut off after that and we went a couple of weeks without any major storms.  You may have forgotten about this brief lull in the action, but the dark purple line in the graphic below shows how the snowpack water equivalent at Snowbird flatlined from November 11 to November 28.  After that, it started snowing, with only some short break...

The northern and western Alps are generally off to a good start to the ski season, but there are some caveats.  Given our current snow drought, I thought we would have a look, focusing on the eastern Alps of western Austria and northeast Italy.   Below is an analysis of total snow depth from the avalanche.report.  This is based on computer modeling and includes observations in colored circles.  Due to frequent northerly and northwesterly flow storms, snow depths are greatest (and impressive) at upper elevations along the northern Alpine Rim, especially near the Arlberg Pass (resort areas of Zurs, Lech, and St. Anton) and in the Karwendal Alps immediately north of Innsbruck.  Snow depth is lower, but still very healthy for this time of year, in the inner Tyrol (resort areas of Ischgl, Obergurgl, Sölden).   On the other hand, the Dolomites of Northeast Italy are really hurting.  The highest snow depth I could find there was 53 cm (about 21 inch...

'Twas a cold but beautiful Christmas Eve in upper Little Cottonwood Canyon.  Alta was solidly above the clouds through our departure at 2 PM.  The photo below taken at about 11:30 AM from Gunsight shows the low clouds lingering over the Salt Lake Valley and in portions of the lower canyon.   By about 2:15 as we were headed down canyon, patch low clouds had reached the Snowbird base area and producing just enough ice crystals to produce a halo.  Very pretty.   Photo: Libby Snethen The clouds were likely forming just beneath an elevated inversion that had its base near 700 mb (10,000 feet), as suggested by the HRRR analysis for 1800 UTC (11 AM MST).   We normally think of inversions as being near the valley floor, but they are typically elevated when we are downstream of an upper-level ridge.  They descend with time as the ridge moves overhead.  That will happen over the next couple of days.  In fact, if you look at the HRRR fore...

It's been some time since we had a significant storm.  The Alta Snowfall History pretty much shows a flatline since December 8th, other than a slight blip for the 1.5 angry inches we got yesterday.   Source: Alta Ski Area That snow was mainly at high elevations.  Lower elevations saw rain.  I miss winter storms. The models suggest scant chances for precipitation until the 23rd, so basically nearly 2 weeks without a major storm.  For Alta, most of the downscaled NAEFS ensemble members are producing less than 0.75" of water and 7.5" of snow, but perhaps 25% of the members are more excited.   Overall, the odds of us getting a minimal Goldilocks storm with 10" or more are fairly low.  I try to be religiously neutral for this blog, but desperate times call for desperate measures.  It could be that all that is needed is a bit more Christmas spirit.  If it worked for Santa in Elf, it can work for Wasatch skiers.  

Last night, the cold pool beneath the inversion got shallower and the upper Avenues emerged from the smog.  I took the photo below from near 13th Avenue on my way into work.  It shows the clear skies at upper bench level, but also the thin lens of smog enveloping downtown and the lower valley.   Upper air soundings collected at the airport yesterday morning and this morning show very subtle but important changes.  Yesterday morning, the inversion base was elevated and near 860 mb (about 400 to 500 feet above the valley floor.  Beneath the inversion was the valley cold pool that contained the fog and low-level stratus clouds.  The flow was weak in and above this layer and didn't reach 20 knots until about 775 mb (about 3300 feet above the valley floor).   Source: SPC This morning, however, the inversion is based right on the valley floor and temperatures below about 800 mb (about 2500 feet above the valley floor) have warmed, whereas they have...

Salt Lake City descended into Inversion Hell with the development of low clouds and increasing PM2.5 levels. Today's MODIS imagery, taken around 1:30 PM local time, showed the coverage quite well with widespread low clouds (in some inastances fog) over much of the central Great Salt Lake, Skull Valley, Tooele Valley, northern Salt Lake Valley, and Davis County.   During the satellite overpass above, the avenues foothills were cloud free, but that changed at around 4:30 when the clouds pushed into the upper Avenues. The fog and low clouds would only be depressing if they weren't also accompanied by poor air quality.  Observations from Hawthorne Elementary along 700 East in Salt Lake City show a major increase in PM2.5 concentrations today to 45-49 ug/m3, solidly at Unhealthy for Sensitive Groups levels.   The high temperature today at the Salt Lake City International Airport was only 32˚F.  For comparison, the maximum temperature on Mt. Baldy (11,000 ft) abo...

It's early in the season, but I thought we could take a quick peak at the western US snowpack .  Technically, this is through 11 December so that I could use many of the State of California snow measurement systems to get a more complete picture of the Sierra snowpack. Then again, maybe I shouldn't have done that since things are fairly dismal in the Sierra Nevada.  The snowpack in the Sierra sits at less than 50% of median.  It gets worse the farther south you go.       Source: NRCS Most of the Cascade Mountain basins are below median.  If you look carefully, there are a small number of stations that are well above median.  Curiously, these are low elevation sites that don't always have much of a snowpack.  For example, the Pepper Creek SNOTEL in southwest Washington was at 300% of median on December 11th, which sounds fat, but in reality, they had only 1.4 inches of snowpack water equivalent.  Thus, the percentage relative to med...

If you are into cold, northwesterly flow snow, I have a treat for you.  Today we are getting an appetizer of mountain snow showers and valley rain showers that won't add up to much, but it gets more exciting late tonight and early Friday morning when a cold trough drops into northern Utah.  The latest GFS puts the primary trough axis at 500 mb and associated unstable northwesterly flow at 700-mb over Utah by 1200 UTC 8 December (5 AM MST Friday).   I hate to say this as I think it could be a jinx, but the pattern looks really great through the day on Friday with the northwesterly flow locked in as another embedded trough with a reinforcing shot of cold air moves into Utah by 0000 UTC 9 Dec (5 PM MST Friday).   Through 11 PM MST Friday, the GFS is generating 18.9" of snow (about 2" of this is from today) with snow-to-liquid ratios generally near or above 15:1.   The HRRR is a bit drier and has slightly lower snow-to-liquid ratios, but is still cran...

Mother Nature gave us the storm we needed.  Water and snow totals per this morning's Utah Avalanche Center are 3.38-4.66"/40-50" in the upper Cottonwoods and 1.80-2.58"/20-30" on the Park City Ridgeline.  Big totals as well in the northern and southern Wasatch.  All northern and central Wasatch SNOTEL sites are at or above the 1991-2020 median for the day except Thaynes Canyon which sits at 86%.  Sorry Wasatch Backers.   I thought we would take a look back at a few forecasts for the event, starting with the ensembles.  I'll just use the ones for Alta Collins that I included in prior blog posts and will use the range of water equivalent and snow reported for the upper Cottonwoods for verification.  The Alta-Collins numbers would be at the top end of this range.   The 3.38-4.66" of water was in the upper 12-22% of water equivalent forecasts produced by the downscaled NAEFS from 00Z 29 November.  For snow, however, we were much closer ...

The skiing and snowpack situation yesterday was somewhat better than expected, making for a decent day with some deep powder.  Many people were out and tracks were laid all over upper Little Cottonwood and environs.   A noticeable density inversion lied beneath a couple of inches of low density powder that fell just before and while we were touring.  Call me a snob, but I felt that made for "hard rock" powder skiing rather than "easy listening."  One definitely had to think about keeping the skis from diving.   The storm continues today and I've elected to work rather than fight Mother Nature in the backcountry or  lift lines at the resorts.  I suspect for the former, the snow is too deep for good skiing on the sub 30 degree slopes I'd be inclined to ski today and for the latter it may take some time until terrain is opened and then it will be limited.   As of 8 AM, the Collins stake at Alta has recorded 9 inches of snow since midni...

The first two waves of our storm cycle delivered in spades yesterday and last night with 23" of snow on the Collins interval stake and 0.78" of water equivalent as of 6 AM this morning.  The .78" includes .03" from just before the 24-hour period listed below.  The snowfall numbers above are higher than being reported by the resort.  I'm not sure if that means the interval stake measurement was affected by wind transport.  Automated snow measurement is hard! The storm started yesterday with very low density snow and overnight the winds blew like hell with peak gusts of 100 mph at 11,000 feet.  The weather and snow section of this morning's Utah Avalanche Center report suggests that many courageous dendrites died last night before they could be skied.  I guess we can take solace in the fact that their remnants will help build the early season snowpack that we so badly need.   Looking at the latest models, I can't help but think, avalanche conditions...

The much anticipated storm cycle is upon us.  It is already snowing what appears to be pixie dust up at Alta.  Automated observations show 2" of new snow from .03" of water, which would be less than 2% water content if accurate.  The latter may be underdone, but it certainly looks light and fluffy on the snow-stake cam and pictures never lie, right?  The models are now in pretty good agreement on the general characteristics of the storm through 0000 UTC 3 December (5 PM MST Saturday), so I'll start with that period.  There will be a crest-level (10,000 ft) trough passage at around 2 PM MST this afternoon and then a second one at 11 PM MST tonight.  I've identified each of these in the HRRR-derived guidance for Little Cottonwood Canyon below.  Then there's a third trough passage at around 5 PM MST Saturday, and this is where we start to see a good deal of model divergence.  Through 5 PM MST Saturday, the models are calling for persistent, moist, we...