Wasatch Weather Weenies

As of 7 AM this morning, Alta-Collins has had 22 inches of snow since 10 AM yesterday with 2.08 inches of water.  Total snow depth is now at 96 inches, putting us at the precipice for Steenburgh Winter (100 inches at Alta-Collins before 10 February).   A big contributor to the water totals was an intense snowband that setup in the southwesterly flow along the Alpine Ridge between Little Cottonwood and American Fork Canyons.  Below is a screenshot showing the band at 23:43 UTC (4:43 PM MST).   From 2300–0200 UTC (4-7 PM MST) Alta-Collins recorded 1.06" of water equivalent snowfall, including 0.42" in the hour ending at 0100 UTC (6 PM MST), for an average of 0.35" per hour.  Anything at or above 0.3" really gets my attention as being out there for Little Cottonwood Canyon.  The Alta-Collins snowstake camera at 6:12 PM MST showed a dome-like pile of large graupel consistent with strong convection within the band.   Little wonder that SR-21...

 A few thoughts on snow and weather as we approach the last weekend of the holiday period. It's been a decent week for skiers like myself who aren't interested in warm weather and bluebird skies.  Conditions at Mountain Dell and Round Valley have been good for skating and I've had a couple of good tours in low-angle trees as well.   I normally exile myself from the Cottonwood Canyons during the holiday week, but toured twice in Big Cottonwood, finding no lineup at the bottom and parking for our group at Spruces.  This is a small sample size, but the traffic has seemed surprisingly manageable.  Perhaps pay-to-park or the lack of sunny skies has helped.  Things may change tomorrow when the Wasangeles Snakers may be coming back to town after tonight's big dump.  There may also be <gasp> sun this weekend, especially on Sunday.   Snowpack relative to median in the central and northern Wasatch is either near- or below median depending on...

The term snow squall has recently and forcefully entered the vernacular of Utahns as a series of strong cold fronts with intense bursts of snow and wind have moved through northern Utah over the past few days.  The most recent was yesterday afternoon. Credit: Andrea Steenburgh It promoted the issuance of snow squall warnings by the National Weather Service.   I received notification by cell phone and saw a very detailed discussion of its movement through the metro area by broadcast meteorologists, which is exactly what one would hope would happen to alert people to the rapid change in weather and road conditions.   Snow squalls are not new phenomenon.  The term is commonly used in the northeast United States where snow squalls can be produced by fronts, lake-effect storms, and other phenomena.  Here in Utah, it has sometimes been used to describe bursts of snow associated with lake-effect storms, but less commonly to describe bursts of snow associate...

As of 1 PM MST 26 December, Alta-Collins has recorded 25" of snow and 2.78" of water since 0000 MST 23 December.  The meteogram below shows the major storm periods quite well.   I suspect most people feel the storm cycle has underperformed thusfar, so let's take a look back.  Below is the GFS-derived forecast from our blog post on 22 December.  I've added a red dot on the accumulated precipitation and snowfall traces.  The GFS was going for 3.17 inches of water, about 15% greater than observed.  That's actually not too bad for a single model.   If we look at the downscaled NAEFS, we're on the low-end, but within the range of forecast water equivalent.     My view is that the total water equivalent forecast by the GFS and the NAEFS wasn't too bad.  However, there were two important shortcomings.  The first is that the GFS and most NAEFS members called for the storm on Thursday and Friday to be much larger than observed...

The model forecasts for the next "sevenish" days are about as good as I've seen in a long, long time.   The downscaled NAEFS product has action starting during the day tomorrow (Thursday) and the pattern remaining active through the period we generate forecasts for, which ends at 0000 UTC 29 December (5 PM MST Tuesday 28 December).   Through that time, the driest ensemble members generate almost 4 inches of water equivalent and just over 50 inches of snow.  The wettest put out ridiculous numbers around 10 inches of water and 150 inches of snow.   This product has been on the wet side this year, but lets pessimistically cut these numbers in half.  That gives a range for water of 2-5 inches and snow of about 25-75 inches, with ensemble means of about 3 and 50 inches.  Wunderbar! Our GFS-derived forecast for upper Little Cottonwood is generating just over 4 inches of water through 11  PM Tuesday, which converts to just over 50 inches of sno...

The upper-level pattern is setting up to make the holiday week a stormy one in northern Utah.   Below are the average 500-mb height anomaly forecasts from the GEFS ensemble valid at 0000 UTC 25 December (5 PM MST 24 December) and 0000 UTC 29 December (5 PM MST 28 December).  The 500-mb level is a good proxy for the upper-level flow.  Anomalies are departures from the long-time average 500-mb heights.  Positive anomalies indicate anomalous ridging, negative anomalies anomalous troughing.  The images below show persistent ridging over the central Pacific and troughing along the Pacific Coast, a pattern that can be very good for northern Utah snowfall provided it doesn't become too amplified (i.e., the trough along the west coast becomes too deep).   Source: NOAA/ESRL/PSD Consistent with the upper-level pattern, our downscaled NAEFS ensemble product for Alta-Collins shows a major shift in the pattern beginning around Thursday December 23rd.  Unt...

Sorry to be Donnie Downer here but regardless of how much snow there might be in the Salt Lake Valley right now, the mountain snowpack situation in northern Utah remains well below median except on north aspects in Little Cottonwood Canyon and the south side of the high Uintas.  The latest numbers from NRCS SNOTEL stations show we are at 69% of median in the Jordan/Provo/Utah Lake basin, 69% of median in the Weber River Basin, and 68% of median in the Lower Bear.   Northern Utah stations at or above median include Mining Fork in the Stansbury Mountains, Snowbird, and several sites on the south side of the High Uintas.   Focusing on the Jordan/Provo/Utah Lake basin, the reality is that the water equivalent of snowfall so far this year has been sufficient to put us at median.  The problem is that some of that snow fell in October and early November and didn't survive.  One can see this in the time series below, which shows several early season storms fol...

KUTV viewers are the best! Ben Agi and his wife captured our #thundersnow in SLC! ⚡️❄️ #utwx pic.twitter.com/6z3ZrvnOts — Chase Thomason (@ChaseThomason) December 15, 2021 Tuesday night's thundersnow event got quite a bit of attention and is even discussed in this article in today's Salt Lake Tribune .  If you want a deep dive, see An Overview of Thundersnow , and article by David Schultz and James Vavrek that appeared in the journal Weather .  I'm able to access it from my campus office this morning, but there is a chance it is paywalled.   Thundersnow is uncommon, but if you are looking for it, Utah is actually a pretty good place.  The map below shows the number of thundersnow occurrences across the United States from 1961-1990.  The highest number was in Utah and the adjoining Intermountain West.  The upper midwest and the Great Lakes regions are also favored for thundersnow.   Source: Schultz and Vavrek (2009)/Market et al. (2002) Th...

I've been AWOL for a few days attending my daughter's graduation at Arizona State.  It was an outdoor affair with temperatures near 70.   The transition to Utah on our return last night could not have been much more dramatic.  I figured our 8ish PM flight arrival time could pose problems for both the frontal wind shift and the snow, and when we boarded, I thought it would be close.  Indeed, we had reached Provo when I felt the plane slow and turn and I thought "oh oh."  The front just passed the airport, so they held us while they reworked the landing pattern for the northwest wind.   I was worried the snow was probably piling up, but eventually we landed in rain.  By the time we reached the Lyft pickup area, it was, however, full on.  The driver picked us up in a GMC Acadia and I thought we might make it home.  Alas, I asked him about the tires and he said he was getting a new set next week!  Not good.  He barely made it ...

The Quad State Tornado hit the hometown of one of my students, Dallas McKinney, Friday night.  Dallas shares his perspectives on the event below.  We are all grateful that Dallas' family and friends are safe.  All opinions expressed are his own and not necessarily that of the University of Utah or his current or former scholarship/grant sponsors (NSF/NWS/NOAA/NASA). Jim Perspectives on the Quad State Tornado Dallas McKinney University of Utah I wanted to give a brief discussion of the mile-wide (likely EF-5) tornado that hit my hometown of Mayfield, KY Friday night and let everyone know that my family and friends are alright. Although supercells are mesoscale phenomena and tornados are microscale phenomena, they require favorable synoptic environments to spur their development. Attached is the closest sounding from where the tornado formed (Little Rock, AR). Notice the sufficient ML CAPE (~2000), high surface dewpoints (~67), and especially the extreme low level shea...

  After fits and starts overnight with convective graupel showers, full-blown frontal precipitation has developed over northern Utah this morning and mountain snowfall rates have really gone through the roof.  Observations from Alta-Collins show .09" of water equivalent and less than an inch of snow through 5 AM, but since then, there's been 0.29" of water equivalent and about 4" of snow.   Radar at 1433 UTC (0733 MST) shows pretty complete coverage over the northern part of the state.  There are a few holes of lighter precipitation, but for the most part, this is as good as it gets for complete coverage in this part of the world.   In the upper aves, we were just starting to turn to snow at 7:15 AM with trace accumulations on colder surfaces.  This puts the snow level pretty much at 5,000 feet.   When I got to campus, it was mainly rain with a few flakes mixed in.   To the north, a look at UDOT cameras shows accumulating snow ...

The long wait is nearly over, with an approaching storm moving in tonight and affecting all elevations with snowfall tomorrow. It's a three part storm.  The first part features moist westerly flow with precipitation developing this evening primarily over the mountains.   Towards morning, an approaching upper-level trough initiates frontal development over the Great Basin, leading to more widespread precipitation in the vicinity of the front.  By 2100 UTC (2 PM) tomorrow (Thursday) afternoon, the front at the surface (lower-right panel) and 10,000 ft (lower-left panel) is forecast by the GFS to be near or just south of Provo.   Eventually, the frontal system moves out Thursday evening and we transition into post-frontal snow showers that could include lake effect Thursday night and Friday. These periods are summarized in the GFS time-height section for Salt Lake City below (recall time increases to the left).   Our GFS-derived forecast guidance pro...

What the GFS giveth, the GFS taketh away. One shouldn't verify a forecast with a forecast, but the Monday-Tuesday storm that I was encouraged about on Saturday and was thinking 5-10" for Alta Collins has really fallen apart in subsequent model runs.   As an example of how the model trend is not always your friend, here's what the 0600 UTC GFS runs have predicted for snowfall at Alta Collins through 11 PM Tuesday over the past few days. 0600 UTC 2 Dec GFS: 15.5" 0600 UTC 3 Dec GFS: 8.4" 0600 UTC 4 Dec GFS: 6.7" 0600 UTC 5 Dec GFS: 4.3" 0600 UTC 6 Dec GFS: 0.2" Oh the pain and the misery of it all!   The reality is that the ensembles never showed this storm to be a lock and I was clearly overconfident. Below is the 0900 UTC 4 Dec initialized SREF showing a range of near zero to 12".  Lots of uncertainty. Looking at the latest SREF shows a range of about 0-6" through Tuesday night, although most members are now at or below 2".   Sad and...

The meteogram of snowfall at Alta ski area so far this season shows a very good October followed by a fairly dismal November.  Source: Alta Ski Area The total snowfall through October 27 was 67".  Since then, there's only been 21.5 inches with only one "deep-powder day" with more than 10" of snow on November 9.  There has been no measurable snow since November 24.   It's not much of a secret to say that we'll see some "weather" next week.  It's been talked about now for several days.  That always makes me nervous, but let's see what the models say.   After a dry weekend, the transition begins early next week.  First, we have a weakly split system that will approach on Monday and move through Utah on Tuesday.   The latest GFS calls for this to be a 7 incher at Alta-Collins through late Tuesday, whereas the NAEFS ensemble plume has a mean closer to 10 inches.  I suspect something in the 5-10 inch range is most likely.  ...