The Europeans and Americans Simply Cannot Get Along

The overnight Utah Snow Ensemble forecast for Alta-Collins may be the crazies I've ever seen.  Most of the European Ensemble (ENS) members are producing little to no precipitation over the next 10 days including during during the period from 10-11 December (more on those dates in a minute).  The wettest ENS member puts out about 0.8" of water and 11" of snow.  

Some members of the American Ensemble (GEFS) have very different ideas.  There are 31 GEFS members and 10 of them put out more than 1.5" of water just through 00Z 12 December.  Several more put out between 1 and 1.5" of water.  There are some that track with the ENS (hard to see but they are there), but many GEFS members are much wetter.

What gives?

I don't plot or attempt to look at forecast plots like our four panel synoptic diagnostic for all 82 members of the Utah Snow Ensemble.  Nobody has time for that.  So I'm going to start here with the ECMWF HRES forecast that serves as the ENS control and is valid 0000 UTC 11 December.  This forecast captures many of the salient details of the pattern that is going to prevail over western North America the next few days.  A broad, low-amplitude upper-level ridge is centered near the Pcific coast (upper left) with an atmospheric river rolling over this ridge and across the northern US Rockies (lower right).  Heavy orographic precipitation occurs where the atmospheric river crosses major western mountain barriers.

So in the HRES the central Wasatch is just to the south of the action.  There are a few dribs and drabs that make it in, but accumulations are scant.  Most ENS members have a similar forecast.

Some of the GEFS members, however, shift the storm track far enough south to get us in on the action.

Diagnosing the why this occurs in this case is beyond my abilities.  I'll just say that I lean heavily toward the view that the central Wasatch may see some dribs and drabs over the next week but it's unlikely we'll see the game changing major accumulations that we need. 

Mother Nature Delivers the Concrete

Twenty-four hour totals at the Alta-Collins automated observing site added up to 1.79" of water and 15" of snow, yielding a mean water content of 12%.  Snowbasin-Boardwalk came in with 1.26"/8"/16%.  As evidence of the wet, windy, and rimey nature of the storm, I couldn't verify our 70 mph forecast for Mt. Baldy because the sensor rimed and is no longer spinning.  The Utah Avalanche Center report this morning says that "at 11,000 feet the wind is absolutely ripping, with sustained speeds at 50–60 mph with gusts pushing into the upper 70s."  That's good enough for me.  

The Alta-Collins snowstake photo this morning is one of the most comical I've ever seen.  Dense snow apparently carved by wind?  Perhaps with the flow wrapping around the Alta sign?  Who knows.  Come up with your own explanation.  

Snowfall at lower elevations is certainly lower and probably a soggy mess between 6000 and 7000 feet (or higher), but that's just a guess.  

The Cottonwoods might get a bit before things taper down later this morning.  The extended forecast shows that you should continue to root for America.  The European Ensemble (ENS) is giving Alta practically nothing after today.  The American (GEFS) is more generous around the middle of the work week.   

USA. USA. USA.

Friday Morning Update

In the previous post (Windy Storm on Tap) we discussed an approaching storm system that would come in today (Friday), but really pick up Friday night as strong flow and an inland penetrating atmospheric river move into northern Utah. 

That forecast is still on track.  Overnight last night and today we are seeing the dribs and drabs at the leading edge of the storm system, as expected.  Overnight through 8 AM this morning Alta-Collins picked up about .16" of water and 2" of snow and Snowbasin-Boardwalk came in with 0.24" of water and 3" of snow.  

But the big story is not today but tonight when the precipitation efficiency looks to increase as an upper-level trough moves through and high integrated vapor transport (IVT) noses into northern Utah.  The GFS forecast valid 0600 UTC 6 Dec (11 PM MDT Friday) shows heavy precipitation over the mountains of northern Utah (or better put what the GFS thinks is the mountains of northern Utah) as the trough (dashed line below) as the trough moves through.  

Our HRRR-derived forecast for upper Little Cottonwood (click to enlarge) shows relatively light periods of precipitation through 5 PM today (top left), afterwhich hourly liquid-precipitation equivalent rates really pick up as the upper-level trough approaches.  Precipitation rates maximize at around 1 AM Saturday with periods of precipitation continuing through 7 AM tomorrow (Saturday) after which precipitation becomes widely scattered.  

This is a warm and windy storm.  Our forecast winds for Mt. Baldy peak at around 700 70 mph [Apologies for the typo! - Jim] at 4 AM Saturday.  Temperatures overnight are forecast to be around 27 F at Collins and 30 F at the base.  As a result, snow-to-liquid ratios are low and generally less than 10 for the period.  This keeps the HRRR-derived snowfall relatively low and around 13" including the dribs and drabs today.  That said, at this point with the need for base, Cascade Concrete is better than Cold Smoke. 

The overnight six-member RRFS ensemble shows a range of liquid precipitation equivalent of between about 1.1 and 2.3" and snowfall between about 13" and 26".  Thus, the HRRR is on the low end of the RRFS.  

My take is that 1.2-2.2" of water and 12-22" of snow from 7 AM this morning through 7 AM Saturday represent the most likely range of outcomes for Alta-Collins, with much of that coming this evening and tonight.  The water amounts are most important right now to build base.  Let's hope we can eclipse 2".

Looking to the north, the story at Snowbasin is much the same with the overnight period being the wettest and then things settling down towards morning.  Snow-to-liquid ratios are quite low at Boardwalk, which is lower than Alta-Collins and thus warmer in this storm.  I'm expecting this to be a very wet snow event up there.  

The HRRR Skew-T for Ogden shows a freezing level near 775 mb or about 7000 ft.  Conditions are saturated, so that also represents the wet-bulb zero level.  

If we zoom into the plot of wet-bulb zero height with time we see that it just about reaches the altitude of boardwal (~8000 ft) and after midnight the base is below that level.  This raises the possibility of a bit of rain or mixed rain and snow at the base depending on how things shake out.  

The extended forecast after this storm is not great for us, but maybe we can get something.  The GFS, for example, has a monster atmospheric river roaring across the northwest next week.  Batten down the hatches for the Cascades, and mountains of the Idaho Panhandle, Montana, and northwest Wyoming.  Goodness gracious that is a tempest of a forecast for them.  

We're to the south of most of the action.  Best case scenario is we get some storms to dip into our area and get some modest accumulations.  Worst case is we don't get much at all.  Odds favor below average precipitation next week, but if the storm track can dip a bit further south than currently forecast, we could get something.

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.