An Actual Storm??

Light flurries and low clouds out there this morning. Compliments of a shortwave trough moving south and east out of the state. Areas on the east side of the Salt Lake Valley have managed to get a skiff of snow earlier this morning, while other locations saw no accumulations. The Wasatch mountains picked up a few inches of snow over the course of this storm. Ski resorts like Alta, UT managed to squeeze out 3-4". Not nothing, but that amount would be judged as light relative to most storms. 

Left: Alta snow stake; Right: Snowbird snow stake 12/3/2025 

Residual moisture and light northerly to northwesterly flow continues to bring some light snow showers in the mountains of northern Utah and some areas in the central and southern parts of the state. However, conditions should improve and snow showers should gradually taper off across locations as the trough and attendant moisture exists the state over the course of the day. But can't rule out some pop up snow showers in the mountains with diurnal heating this afternoon.

GOES-18 West True Color Imagery 12/3/2025

A brief respite in the weather is expected Wednesday afternoon into Thursday as a transient shortwave ridge brings some subsidence and drier conditions. But, this break in the weather is short-lived. Things start to get interesting again late Thursday into Friday morning as Utah remains firmly within an upper-level northwesterly flow regime. Starting late Thursday, a slug of moisture and energy - associated with an atmospheric river (AR) making it's way inland from the PNW - is expected to descend NW to SE into Utah. Depending on which model you look at (GFS or ECMWF), snow showers arrive across the northern Wasatch Front sometime between late Thursday night into Friday morning and continue consistently or with a few breaks through Saturday. Heaviest snowfall rates in the mountains look to occur late Friday through Saturday afternoon.

ECMWF 00Z 12/3/2025 four-panel forecast 12/3-12/8/2025: (Top left to bottom right) MSLP/precip and 1000-500 mb thickness; 300 mb gph and winds; ; 500 mb gph, vorticity, and winds; 700 mb gph, RH, temp, and winds

Generally speaking, deterministic models have been struggling all week with how far south this storm will dig into Utah, but have now reached more of a consensus that this storm will bring a robust push of moisture with an accompanying jet streak into central to northern Utah the first half of this weekend. Additionally, jet streak dynamics look to be more optimal than previous model runs, with the left front exit region (LF) of the jet setting up across northern Utah Friday through Saturday. The LF region of a jet is typically associated with enhanced large scale ascent/lift due to the balance of forces and mass continuity in the atmosphere.   

Total Precipitation (in) 12/3-12/7/2025 - Left: ECMWF 00Z 12/3/2025; Right: GFS 00Z 12/3/2025

Total Snow 10:1 (in) 12/3-12/7/2025 - Left: ECMWF 00Z 12/3/2025; Right: GFS 00Z 12/3/2025

Timing and precipitation amounts with this weekends storms will still likely vary from current model runs, but I think there is more confidence this will be a substantial snow event for the northern Utah mountains this weekend. Looks like ensembles are calling for at least 1-2" of liquid or 10-20" of snow in favored areas of the Wasatch (i.e. Alta). 

Total Snow 10:1 (in) Alta, UT 12/3-12/18/2025 - Left: ECMWF ENS 12Z 12/3/2025; Right: GFS ENS 12Z 12/3/2025

This will be a warmer storm as it's origins are from the Pacific, so snow levels will initially start low at valley levels on Friday morning before gradually rising late Friday into Saturday to around 7000-7500' as warm air advection brings slightly "warmer" temps across the state. A resurgence of cooler air late Saturday closes out the storm, bringing snow levels back down to the valleys for any remaining showers. In terms of snow characteristics, snow density will see-saw similar to snow levels. 

Alta, UT GFS derived snow density (source: UoU Atmo Sciences)

Snow will likely start out as lighter/less dense early Friday then become heavier/more dense with the arrival of warmer temps late Friday into Saturday. A bit of lighter snow could end out the storm late Saturday as cooler temps return. This means the storm will likely produce a stratified snowpack with lighter-denser-lighter layering. Could loosely be described as having "upside down" (not related to Stranger Things) characteristics. 

Beyond this weekend models diverge quite a bit, with the GFS keeping things active through next week and weekend and the ECMWF keeping things a bit quieter. We'll have to see how things shape up after this weekends storm.