Windy Storm on Tap

Batten down the hatches because we have storm that might have everything but the kitchen sink in it for the Wasatch Range.

Right now Thursday looks dry, but the leading edge of the storm looks to move in on Friday with some mountain snow, mainly in the northern Wasatch, but probably tickling the central Wasatch some too.

Then Friday night things really start to get rolling.  The GFS forecast valid 0300 UTC 6 Dec (8 PM MST Friday) call for very strong flow (red ovals) to move over a low-amplitude ridge that is centered west of SoCal.  This leads to the inland penetration of an atmospheric river, as indicated by the filament of high integrated water vapor transport (IVT) that extends from southern Oregon to northern Utah (red arrow).  

This general pattern persists until Sunday morning, although flow, IVT, and precipitation intensity weaken late Saturday (if forecasts hold).  

The Utah Snow Ensemble forecast below focuses on the 24-hour period ending 0000 UTC 7 December (5 PM MST Saturday).  That is probably the wettest part of the the storm.  The ensemble mean for that period is 1.0" at Snowbasin and 1.2" at Alta-Collins (upper right panel).  

The Alta-Collins plumes show a bit of precip on Friday, but things really picking up Friday night.  and persisting until Sunday morning or later in a few members.  

The GEFS ensemble is more bullish on precipitation than the European (ENS).  As I said in the previous post, it's important to be rooting for America and that continues to be the case in this forecast.  

The median water and snow forecast by the ensemble from 5 AM Friday to 5 AM Sunday is 1.5" and 16.2" respectively.  Perhaps a reasonable estimate for snowfall totals during that period is 10-20", although the distribution above skews to higher values so the odds of more is probably greater than the odds of less.  A lot will depend on details that are hard to reliably anticipate this far ahead.

I suspect we will also see wind and rime.  New lifties for riming-prone lifts may have a real initiation Saturday morning.  Good luck. 

I'll see if I have time for a closer look on Friday. 

Limping into December

November is in the books and except for the last day we can be glad it is in the rearview mirror.  The last day did bring a bit of snow to the Salt Lake Valley, resulting in a beautiful start to the morning today. 

Avenues Twin Peaks from University of Utah Campus 1 Dec 2025

That said, it was a bad month for skiing due to warmth and lack of snow.  At the Salt Lake City International Airport, this November was the warmest on record.  

Records in the mountains are spottier.  At Alta, the Average temperature was 37.5°F, which is the 2nd highest on record, but observations there are much spottier and I don't put much faith in that number.  The warmest November on record there (1949) has 9 missing days.  It's safe to say it was warm, but definitive statements are not possible with the historical record at mountain sites due to limited data. 

So we limp into December.  The next storm system comes on Tuesday night.  It's another system dropping in from the northwest with some similarities to Sunday's storm in that it will likely produce snow or a rain/snow mix on the valley floor with accumulations of a trace to 2" in the valley and perhaps a bit more on the benches.  Worth watching forecasts in case this changes.  

For Alta-Collins, there's pretty big spread in the models with some giving less than 2" and the biggest outliers being in the RRFS ensemble where there are two members in the 8-9" range.  

Think 3-6" and hope for more. 

After that, the forecasts range from sad to optimistic.  The Utah Snow Ensemble shows that most members of the European ensemble (ENS, yellow-orange liens below) are calling for a bit more snow later in the week and into the weekend.  The mean of the ENS is perhaps another inch of water and 10" of snow, although there are a few of ENS members going for game-changing amounts in excess of 30".

The US ensemble (GEFS) has more members who are putting out much bigger amounts over a multiday period, yielding a mean snowfall of 40" over the next 10 days.  The difference between most ENS members and most GEFS members is the storm track with the ENS members tending to be a bit stronger on the western ridge, resulting in a drier forecast (although we still get some snow), whereas the GEFS members bring more action into northern Utah.  

Bottom line is that you should be rooting for America. 

All Elevation Snow Possible Sunday

Thanksgiving weekend looks to conclude with a storm that will likely produce some snowflakes at all elevations in northern Utah. It's not a big storm, but being the first that might bring winter driving conditions to some areas so far this season, at the end of Thanksgiving weekend, it's worth monitoring if  you will be traveling.  

The storm will be produced by an upper-level trough and cold front that will drop into Utah on Sunday from the northwest.  Below is the GFS forecast valid 1800 UTC 30 November (11 AM Sunday) showing the trough extending across northern Utah and Nevada.  

Below is the HRRR forecast sounding for the Salt Lake City International Airport valid 1800 UTC 30 November (11 AM Sunday).  It shows saturated conditions down to the valley floor with temperatures just above 0°C.  

The HRRR keeps surface temps just a smidge above freezing as the front moves through.  If that were to verify, the most likely outcome would be snow for the benches and wet-snow for the lowest elevations near the Great Salt Lake during the passage of the system.  If it were a bit warmer, then perhaps it would be a rain/snow mix at those lowest elevations.

 Below is our HRRR-derived snowfall guidance which suggests 1.6" at the airport, 2.6" at Cottonwood Heights, and 8.4" at Alta-Collins.  This product does not, however, consider on-the-ground melt, which could be an issue on the valley floor and might limit actual accumulations there.  A lot will depend on the snowfall rate during the passage of the system. 

We can also have a look at the 6-member RRFS ensemble.  It appears to be a smidge warmer than the HRRR as most members are producing 0.2" of water or more at the airport, but snowfall is scant with one member getting up to a bit under an inch.    

For Alta-Collins, five of the six members are coming in between about 3.5 and 8", but there is one very optimistic member going for close to 18.  There is always hope. 

So to summarize, a trough and frontal passage will be bringing precipitation to northern Utah on Sunday.  Snow is expected and bench and mountain locations.  At the lowest elevations, temperatures are such that we could see wet snow or a rain/snow mix.  It's worth monitoring the weather and road conditions if you need to travel on Sunday.  

Thanksgiving Weekend Cold Front

There's still not much to get excited about in the forecasts.  The main weather feature of interest over the next several days is a cold front that is currently forecast to be moving through Utah Friday night.  

Below is the GFS forecast valid 0600 UTC 25 November as an example of one model forecast showing some precipitation over northern Utah as the cold air is pushing in.  

Right now, this looks like a "quick hitter" variety of storm.  The GFS is putting out 0.57" of water and 8" of snow for Alta-Collins through 5 AM MST Saturday.  The Utah Snow Ensemble members are less enthusiastic with a median of 0.09" of water and 1" of snow through that same time, although some members are slower with the system and give us some more into Sunday.  Still it's not a lot.  The snowiest member is putting down 20",. but that's not a likely scenario and perhaps we wore out our luck with the U's improbable win over K-State on Saturday.  If we could get a few inches at Mountain Dell, maybe the Nordies would be in luck.  That's possible but not probable.  

Snowmaking conditions will, however, improve.  There will be guns blazing.  

Ghosts of Thanksgiving Past

Thanksgiving weekend 2001.  

We traveled to with the kids to Seattle to enjoy the annual feast with family.  

When we departed, most likely on November 21, there was no skiing.  A look at the Alta-Collins data on MesoWest suggests a 10" natural snow depth.  My recollection was that there was no snow, but perhaps their was a little.  

When we returned, there was skiing.  Plenty of skiing.  

At around 0000 MST 22 November 2001, the start of Thanksgiving Day, it started snowing.  Eventually, 108 inches fell at Alta-Collins, including one hundred inches in one hundred hours.  The press called it the hundred inch storm.  Pretty catchy.  It led to one of the funner papers I've written during my career. 

The hundred inch storm was really produced by two storms or should I say two frontal systems.  Snow at Alta came ahead of each front, with each front, and behind each front, with both post-frontal periods producing incredible lake bands.  

Example radar imagees from the two lake-effect bands that contributed to the Hundred Inch Storm. Source: Steenburgh (2003).

One of my former graduate students, Kristen Yeager, went back several years later and found that the second of the two lake-effect periods was the largest on record from 1998, when KMTX radar archives began, to 2009 when she ended her study.  It produced an unbelievable 3.15 inches of water at the Snowbird SNOTEL.  We really haven't seen anything like it since, so it most likely was the biggest lake-effect storm since 1998 and possibly since the installation of the radar in 1994 (radar data from the first few years of KMTX operations were not archived).  

The snow depth time series from Alta-Collins for the period shows it becan with a scant 10" or snow on the ground (sometimes the calibration of the depth sensor is off so it's possible it was less than this).  The first storm raged through early on the 23rd when the snow depth reached 50".  Then there was a break.  Then the second storm pushed the total depth to 80".  Roughly a 70" increase in four days. 

Source: Mesowest

That number is less than the 100" total because the total snow depth is subject to compaction whereas new snow totals are based on interval samples on a snow board.  

The Salt Lake Tribune ran the photo below of a what appears to be an Alta Ski Patroller getting the goods following the storm.  

Source: Steve Griffin, Salt Lake Tribune

My notes indicate the east bench got 30-33" and the Salt Lake City airport 15".  I do remember having to dig the car out from the airport parking lot when we returned.  

Things can change fast.

A Pretty Splitty Pattern

The mild first-half of November is now in the books.  The Salt Lake City International Airport came in with the warmest on record with an average temperature of 53.0°F.

Source: https://xmacis.rcc-acis.org/

Last night's storm dropped about 4" on Alta Collins.  Not much to get excited about.  I haven't looked carefully, but the big winner appearred to be Ben Lomond Peak which got about 2.3" of water and had a total snow depth of 10" at 5 AM this morning.  

The pattern continues to look splitty for the next few days.  Just an an example, below is the GFS 500-mb height (contours) and wind speed (color fill) forecast valid 2100 UTC 20 Nov (2 PM MST Thursday).  The Pacific Jet is forecast to be well consolidated near 150 W but split upstream of the North American coast into two branches, one moving through western Canada and the other over northern Mexico.  

The various ensemble forecasts either keep us dry or give us some light amounts as systems in the southern branch of the jet brush by.  The Utah Snow Ensemble forecasts for Alta-Collins from last night show a bit with last nights storm through about 25 November, most members give us scant precip. 

A few push the southern track storms far enough north to give us some decent water and snowfall totals, but there are only a few of these.  At least 75% of the members give us less than 10" of snow and less than an inch of water.  

Paraphrasing Thomas Paine, these are the times that try ones soul.  The summer lover and sunshine worshiper will, in this crisis, shrink from the mountain climates; but one that stands by it now, deserves the love and thanks of powder when it returns.