Wasatch Weather Weenies

As I write this, dawn is breaking on the final day of January, which promises to be the nicest weather day of the winter so far with our deepest snowpack, fresh snow (although probably tracked out in resort terrain that was open yesterday), and bluebird skies. Sadly, it sounds like there was another fatality yesterday in the backcountry adjacent to the 9990 chair at Park City Mountain Resort.  We have talked previously about the high frequency of fatalities there and some of the heuristic traps that contribute to them (see The Lure of Dutch Draw ).  Today has all the hallmarks of the type of day that causes skiers to push it into steeper terrain with fresh snow, beautiful weather, and a season of pent-up powder frustration.  Don't let Powder Fever cloud your judgement.   We have another shot at a major winter storm Tuesday night and Wednesday associated with an upper-level trough passage within large-scale northwesterly flow.  Below is the GFS forecast vali...

 

Rumors are its snowing in the Wasatch.  I see about 6" since yesterday on the Collins Stake at Alta and Ski Utah's morning report advertises a max for the Wasatch resorts of 9" at Brighton.   Peshaw! Excuse me for being distracted, but my eye's gaze is drawn to the Sierra. Other than a bit more of a bend and northward shift in the precipitation band, the radar over central California changed little overnight.  Heavy precipitation associated with an atmospheric river continues to have its crosshairs aimed at the Sierra Nevada. The main change is the northward shift, which has allowed the Sierra around Lake Tahoe to get more snow overnight after a bit of a lull yesterday. Here are some changes in total snow depth based on automated sensors in the Sierra Nevada from Squaw Valley to Mammoth Mountain from 1800 UTC (1000 PST) 26 January to 1200 UTC (0400 PST) 28 January: Belmont-Squaw Valley (8000’): 25” Roundhouse Bottom-Alpine Meadows (6950’): 21” Caples Lake Near Kirkwo...

Today is one of those days when I look at the observations coming in and I keep redoing the math in my head and asking myself if I'm doing it wrong.  The numbers from the Sierra Nevada near Mono Lake are ASTOUNDING.  For much of the night and day, that area has been in the crosshairs of an atmospheric river and slow moving frontal precipitation band.  Below is the synoptic situation as of 2100 UTC (1400 MST) showing heavy precipitation over central California in the southwesterly flow ahead of the upper-level trough (note that portions of the Sierra have poor radar coverage.  Twenty-four hour snow depth change diagnosed from automated sensors shows the heaviest snowfall in the eastern Sierra near and around Mono Lake, including an increase of more than 20 inches at one site.  Most of this snow has fallen in a period of about 15 hours (ignore the 39 near Lake Tahoe which may be eroneous).   Not shown here are observations from Mount Rose in the Carson R...

 Continuing with our theme of lyrics from 70s pop songs in this week's posts, Albert Hammond once sang, "it never rains in southern California, it pours."  I'll take artistic license and extend that more broadly to the Sierra Nevada and snowfall. Model forecasts for the Sierra in the coming days are pretty incredible.  The setup is a deep, cold cyclone and upper-level trough dropping down out of the Gulf of Alaska, with a slow-moving cold front and atmospheric river stalling over central California and the Sierra Nevada.  Below is the GFS forecast for 1500 UTC 27 January (8 MST Wednesday) showing the situation during the early stages of the storm, with the front just south of the Bay Area and heavy precipitation in the Sierra Nevada.   Below are GFS integrated vapor transport forecasts showing the southwesterly flow and transport of moisture associated with the atmospheric river near and ahead of the front at 1200 UTC 27 Jan (0500 MST Wednesday) and 1200 UT...

The weekend snowstorm and powderfest notwithstanding, the snowpack situation in northern Utah remains dire and it is important that you all continue to provide sacrifices to Pagan gods so that the situation improves.  Human sacrifice not recommended, but please consider other legal options. Alta ski area's web site reported totals through Sunday morning of 22".  The hourly interval stake observations from Alta-Collins indicated 19".  In either event, it was a good storm.  Several of my colleagues at the University of Utah in Mechanical Engineering and Atmospheric Sciences are testing out a new measurement system at Alta-Collins that provides very high-frequency measurements of snow density (expressed below as water content).  Below is what they found with the first couple of inches varying around 10% and then the next several inches varying around 8-9%, before some larger fluctuations for the last couple of inches.    Source: https://my.mech.utah....

It is, as my ski-touring friends like to say in situations with a hair-trigger snowpack, a good day for a walk in the woods.   Storm totals as of this (Saturday) morning as reported by the Utah Avalanche Center include 16" (1.42" SWE) in upper Little Cottonwood, 15-20" (0.95"-1.50" SWE) in upper Big Cottonwood, 10-13"  (.85-1.2" SWE) on the Park City Ridgeline, 14" (1.30" SWE) in Mill Creek, 10-12" (1.0-1.23" of SWE) in the Provo area mountains, and 8-12" (0.50-1.10" SWE) in the Ogden area mountains. Basically a little something for everyone, with more to come.   Not surprisingly, snow-starved Salt Lakers were out in full force this morning.  Alta reported full parking lots at 8:12 AM, a full hour before the scheduled opening of the lifts at 9:15.   All parking at Alta is now FULL. @UDOTcottonwoods https://t.co/MrWsId5XVS — Alta Alerts (@AltaAlerts) January 23, 2021 In some years, a 16" storm might make for great b...

For those of you who use weather.utah.edu, my apologies for the very long outage of model graphics and derived products.   We have occasional outages sometimes due to computer or networking issues at the University of Utah. We also have them from time to time due to crappy programing on my part.  The current one, however, is due to scheduled downtime of the NOAA server that serves as host for model data produced by the National Weather Service. Such downtime is typically postponed if the National Weather Service declares a "critical weather day," but neither yesterday or today met the criteria for such a day outlined at  https://www.nws.noaa.gov/directives/sym/pd01022003curr.pdf .  The potential for heavy snowfall in the Wasatch certainly apparently meets critical weather day status for us, but not the nation.  Thus, the downtime went forward as scheduled.    The last update issued on the server was at 1339 UTC (0639 MST) when a statement was issu...

The three most important things in real estate are location, location, and location, and that's often the case for winter storms in northern Utah.  The position of precipitation systems can make or break the forecast at a given location, and that's the case for the Friday-Saturday storm that we've been hoping for over the past several days.   The storm has at least two parts and possibly more depending on how things come together.  Due to scheduled downtime of the National Weather Service server that we get our model grids from, I'll be using the 1200 UTC NAM forecast from this (Thursday) morning to illustrate these parts. The forecast for 1500 UTC 22 Feb (0800 MST Friday) shows a deep upper-level trough over the northern California coast.  At this time, there's only spotty precipitation in the southwesterly flow over the southwest US, including Utah.   However, during the day tomorrow, due to the strong dynamics associated with the trough, things mois...

January has brought a whopping...wait for it...16.5 inches of snow to Alta through January 19.  That's not a lot, but many driving through Little, Big, or Parley's canyon got bit by the red snake anyway.   Highway impacts from winter storms depend on several factors.  Snowfall amount can matter, but snowfall intensity, pavement temperatures, traffic, timing, and other factors can cause even storms with relatively small totals to cause huge problems.   Twenty-four hour snowfall total in the central Wasatch through this morning are in the 1-3" range.  However, most of that snow fell in the late afternoon with relatively high intensity, especially west of the crest, strongly affecting road conditions in the canyons.   Source: NCAR/RAL The situation at the time was a bit unusual.  Winds at mountaintop level (e.g., on Mt. Baldy and at the top of the Snowbird tram) were weak and northerly as we were beginning the transition to the easterly flo...

The Tokyo Climate Center of the Japan Meteorological Agency just released a report discussing the heavy snowfall observed in Japan in recent weeks.  If you want the gory details, the report is available here .  The figures below are from the report.   As detailed in the report, beginning in mid December, an anomalous jet-stream pattern led to frequent cold air outbreaks from interior Asia over the Sea of Japan, which was anomalously warm.  72-hour all-time or January snowfall records were broken at 19 stations, spanning nearly the entire length of Honshu.   There are a couple of things that stand out for me in the image above.  First, there are some stations well inland from the Sea of Japan that set records.  These occurred during the mid-December event in which strong flow enabled deep inland penetration and orographic enhancement of sea-effect snowfall (see our previous post Gosetsu Chitai Dumpage for more information).   Second...

Many people equate pollution in the Salt Lake Valley with the inversion, but they are different but related phenomenon. Understanding the difference between the two explains unusual days like yesterday when haze and smog filled the Salt Lake Valley through a relatively deep layer, extending up to about 7500 feet.  This occurred not because the inversion was deep , but because the inversion was elevated .  In addition, the atmosphere below the inversion featured weak stability, enabling pollution to mix through a relatively deep layer.   The image below includes a photo taken yesterday morning from Alta Ski Area and the sounding taken that afternoon at the Salt Lake City International Airport.  Haze and smog filled the Salt Lake Valley to an altitude of about 7500 feet where there was a sharp boundary to clearer air (indicated by the dotted line).  The afternoon sounding showed that in that haze and smog layer, the stability was relatively weak. Meteorologis...

Low overcast clouds that fill the lower elevations of mountainous regions are sometimes referred to as valley stratus .  They can occur any time of year, but are most common during the cool-season when the energy input from the sun is low, enabling the stratus to be more persistent.   We are experiencing valley stratus in the Salt Lake Valley today, with mostly cloudy skies. However, the highest elevations of the Wasatch are above these clouds.  Note the contrast below between the lower and upper mountain at Snowbird. Source: Snowbird Source: Snowbird Satellite imagery shows an interesting transition in the valley stratus today.  At around noon, the stratus was confined to near the Great Salt Lake, which was fully covered by clouds.  Visible satellite imagery at 18:56 UTC (11:56 AM MST). Source: College of Dupage An hour later, stratus was developing along western slope of the Wasatch Range and within the Salt Lake and Utah Valleys immediately upstream....