Wasatch Weather Weenies

Snow is currently short of scant in the Wasatch with 6" being reported by the Collins automated sensor and spotty coverage on high-north aspects. Alta Ski Area cam image from 8:40 AM MDT 31 Oct 2025. Source: Alta Ski Area. While there's no skiing, it does look like a splendid Halloween and weekend for late fall, so enjoy.   Given that we are playing the waiting game for snow, I thought I would share a few thoughts on using long-range forecast guidance.   The National Weather Service Global Forecast System (GFS) produces forecasts at ~13 km grid spacing out to 16 days.  The European Center for Medium Range Weather Forecasting similarly produces a "control" forecast at ~9 km grid spacing out to 15 days with their Integrated Forecast System.  For simplicity I will call this the ECMWF control, although you may know it as the Euro, EC, ECMWF, or HRES.  Plots from these modeling systems are readily available on weather.utah.edu and other sites.  Howeve...

Warm, dry, ridgy weather looks to predominate the end of October and start of November.  All members of the Utah Snow Ensemble have no precipitation at Alta-Collins through 0600 UTC (0000 MDT) Tuesday 4 November.  Then a few get excited, but others a meh, so we will have to see what the storm track decides.  The waiting game is now in full swing.

On Monday we discussed the possibility of big changes this weekend with the potential for a significant snowfall event (see Big Changes Next Weekend ).  Changes are still coming, but right now it appears that the pattern will not be quite as favorable for mountain snow, although there will still be some.   The latest GFS is still bringing a front through northern Utah this weekend.  Below is the forecast valid 0000 UTC 26 Oct (6 PM MDT Saturday) with the front pushing into northwest Utah.  It's still looking like we will have a frontal passage Saturday night with Sunday significantly cooler.   That said, the moisture and precipitation with the front isn't quite as robust as advertised a few days ago.  There's still a decent chance of valley showers and mountain snow, but amounts are not as high.  Then, instead of the trough digging through the western US, it lifts off to the northeast.  We get a bit more precipitation Sunday and Sunday n...

Although this week will be mainly quiet with the exception of a weak monsoon trough that will move across southern Utah Wednesday night and Thursday, next weekend looks exciting. The latest GFS is forecasting a strong cold front to be moving across northern Utah late Saturday.  Behind the front, a strong jet extends across the Pacific and into the western United States.   The European is on board with this general pattern shift, but is faster with the front, which it forecasts to be in eastern Utah by late Saturday.   Regardless of timing, the frontal passage should bring another round of precipitation with it to add to the 4.95" October record at the Salt Lake City International Airport.  Additionally, it also looks to bring mountain snow and even the possibility of valley flakes, although much with regards to that will depend on what happens in the wake of the front.   The Utah Snow Ensemble forecast for Alta-Collins has a few ENS (European Ense...

It's a rarity here in the Great Salt Lake rainforest, but it looks like we have a dry spell settling in that will last through the weekend.   The trough that brought us rain over the past few days is exiting the area today.  On Saturday, a low-amplitude upper-level ridge looks to be moving in, with no monsoon moisture or Pacific storms to be found in our area.   There is a brush-by system that flirts with northern Utah late Sunday but right now the precipitation from that looks not push into Utah through 0000 UTC 20 Oct (1800 MDT Sunday). That system could bring a bit of precipitation to northern Utah, mainly in the mountains, on Sunday night. For Alta Collins, for example, a bit over half of the Utah Snow Ensemble members produce no precipitation Sunday night, but a fee give us some light amounts Sunday Night, with a couple doing a bit better than that.  That's the main threat for precipitation over the next few days if you are hoping to add to aour alread...

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More thunder and rain last night.  Observations from the Salt Lake City International Airport indicate another 0.68" in the gauge, all if it falling yesterday evening and overnight.  If my math is right, that brings the monthly total up to 4.16", topping the previous record for the month of 3.91".  Really, it wasn't even a fair fight.  It's only October 14! With the October record easily dispatched, I thought we might aim higher.  First let's have a look at the records for each calendar month: January 1918: 3.89"  February 1998: 4.89"  March 1891: 4.66"  April 1944: 4.90" May 1908: 5.76" June 1998: 3.84" July 1982: 2.57" August 1968: 3.66" September 1982: 7.04" (!!!) October 2025: 4.16" and counting November 1875: 5.81"  December 1983 and 1889: 4.37" And then additional months at or above 4": March 1876: 4.00" April 1974: 4.57" April 1986: 4.55" April 1984: 4.43" April 1886: ...

Total October precipitation at the Salt Lake City International Airport through October 11 is 3.48".  This is already good for the 7th wettest October on record (tied with 2004).   Ten wettest Octobers on record at the Salt Lake City International Airport. Source: https://xmacis.rcc-acis.org/. The record (3.91") is only 0.43" away.  Average precipitation the rest of the month would eclipse that, so we have a pretty good shot of having the wettest October on record.

Wow, what a forecast.  Buckle up as a lot is going to be happening through Sunday.  Things get exciting around here when the mid-latitude storm track phases with monsoon moisture and we will have both in spades this weekend.   I'll start with the GFS forecast valid 1200 UTC 11 October (0600 MDT Saturday).  A deep trough sits along the Pacific coast and monsoon moisture is streaming into the four corners area, producing the Predecessor Rain Event (PRE) discussed the the previous post in advance of the remnants of Hurricane Priscilla over northern Arizona, southeast Utah, and southwest Colorado.  In addition, a strong cold front sits over eastern Nevada. By 0000 UTC 12 October (1800 MDT Saturday) that strong cold front is over northern Utah and lighting up parts of northwest Utah.   I'm not sure how Saturday is going to play out in the Salt Lake Valley ahead of the front.  There will be southwest flow ahead of the front but it's hard to say if ...

A lot of exciting things can happen this time of year when the mid-latitude storm track interacts with monsoon moisture.  The latest model runs really get my attention in this regard as they are putting out a good deal of precipitation in the southwest US. The latest GFS shows the precipitation picking up in northern Arizona on Thursday.  By 1200 UTC 10 OCT (0600 MDT Friday), precipitation is organized in a band that runs from SW to NE from northern Arizona and to western Colorado.  This precipitation region is to the north and northeast of Hurricane Priscilla, which is forecast to be off the coast of Baja California at that time.  Such a precipitation feature is sometimes referred to as a Predecessor Rain Event, or PRE and occurs as enhanced vapor transport north of a hurricane experiences large-scale lift.  Forecast soundings from Flagstaff at that time are saturated with precipitable water values of 25.4 mm (exactly 1 inch if you prefer US units), which is qu...

Last week we described a new HRRR-derived forecast product for Snowbasin .  So my friends in the central Wasatch don't feel neglected, we've also dropped a similar product for Little Cottonwood Canyon on  weather.utah.edu .  It's available from a link along the top bar or directly at  https://home.chpc.utah.edu/~steenburgh/ml/hrrrlccforecast.html .  It should update regularly, but we're not watching things all the time, so always check the dates before using.   Like the new Snowbasin forecast guidance, the Little Cottonwood forecast guidance is based on the HRRR and uses machine learning to improve the prediction of several variables.  There's a graphical product (the examples below are the forecast from 0000 UTC 4 October and not todays): and a tabular summary: We provide wind forecasts for three locations: Mt. Baldy (AMB; 11,066 ft), Top of the Collins chair (ALT; 10,443 ft), and Cardiff Peak (IFF; 10,059 ft).  AMB is a wind-exposed locatio...

Pretty remarkable water numbers from this latest storm.   At 7 PM MDT, the NWS reported a record calendar-day rainfall of 2.39". The 2.39" appears to be the 2nd largest calendar-day rainfall on record, topped only by the 2.64" on 3 May 1901.   Source: https://xmacis.rcc-acis.org/ In other news, the Collins stake sits at around 8 inches. Source: Alta Ski Area

For a long time, I've neglected our friends in the northern Wasatch, but that is changing this year as we will be conducting a major field campaign focused on that region this winter.  More on that in a future post.  In preparation for that campaign, we just dropped a new Snowbasin forecast guidance product on weather.utah.edu .  It's available from a link along the top bar or directly at  https://home.chpc.utah.edu/~steenburgh/ml/hrrrsnowbasinforecast.html .  It should update regularly, but we're not watching things all the time, so always check the dates before using.   This new Snowbasin forecast guidance is based on the HRRR and uses machine learning to improve the prediction of several variables.  There's a graphical product (the example below is from last season): and a tabular summary: We provide wind forecasts for three locations: Ogden Peak (OGP), Strawberry Gondola Top (SB2), and the Boardwalk snow-study plot (SBBWK).  The first two...

Some high-altitude locations such as the top of Snowbird have already seen their first snow, but on Saturday we may see a bit more wide spread snowfall. The latest GFS shows a bonafide cold trough moving across northern Utah at 1200 UTC 4 October (0600 MDT Saturday) with an accompanying cold front and precipitation system.   Our GFS-derived machine-learened forecast product for upper Little Cottonwood shows temperatures on Mt. Baldy (11,000 ft) and at Collins (9,700 ft) plummeting Friday night and Saturday along with wet-bulb zero levels dropping to near 8000 feet by noon Saturday.  If that verifies, that would probably put the snow level Saturday afternoon around 7500 feet.   For Collins' 9700 foot elevation, the GFS is producing a total of about 0.8" of water.  The storm begins with rain at that elevation Friday afternoon, but eventually changes to snow Friday night.  Total snowfall of just over 4". The Utah Snow Ensemble is a bit more jacked. 75% of...