AR Tease

The mornings as of late have finally gotten that touch of chill characteristic of mid fall. This morning was no different. Not much going on out there, with clear skies and calm winds. Seems to be the precursor to a typical fall day. The light haze we had Wednesday and Thursday has finally dispersed. We can thank some northerly near surface winds yesterday afternoon for sweeping the pollution out of the Salt Lake Valley. Ceilometer data from a site in the northern SLV near the airport reveals how the pollution cleared out of the area once winds shifted N-NW and picked up in the afternoon. 

Top: Observed KSLC wind speed/direction 10/23-10/24/2025; Bottom: Ceilometer reflectivity 10/23-10/24 from the Utah Tech Center (norther SLV).

Friday-Saturday

The closed upper-level low that impacted the state yesterday has exited to the east, with a short-wave ridge following in it's wake and building across Utah today (Friday). Conditions are expected to be clear, calm, and relatively warm Friday, with temps topping out in the mid-60s for the northern Utah valley areas, which is near normal for this time of year. Ridging remains through the first half of Saturday before the upper-level pattern will begin to transition into a more active pattern. Temps will be a few degrees above normal Saturday along the Wasatch Front and winds will become a bit breezy in the afternoon as warm air advection precedes the weekend storm.

Observed 500 mb gph and temperatures (C)

A broad Pacific trough and stream of moisture (atmospheric river (AR)) is currently making landfall along the PNW coast. A short-wave trough and surface low embedded in the larger scale trough will move inland today through Saturday. Models have been tracking the center of this trough across the interior northwest into Idaho and Montana by late Saturday. 

Saturday - Monday

There is still some uncertainty about how shallow or deep the trough digs into the Great Basin and Intermountain West region. Currently, models are taking the system on a more northerly track, with only grazing impacts across Utah. This means the bulk of the moisture and colder air are forecasted to miss Utah late Saturday into Sunday. However, a strong 140 kt jet and stronger area of baroclinicity is forecasted to progress into the far reaches of the state near the Idaho border, which could provide better dynamical forcing for precipitation for Bear River mountains and Cache Valley.

ECMWF 00Z 10/24/2025 four-panel forecast for 10/24-10/28/2025: (Top left to bottom right) MSLP/precip and 1000-500 mb thickness;700 mb gph, RH, temp, and winds; 300 mb gph and winds; 500 mb gph, vorticity, and winds

The northern third of the state looks to have the best opportunity for some rain/snow showers Saturday evening through Sunday, with a cold front moving across the area at the same time. Guidance has trended warmer with the air that moves in behind the cold front, so not looking lower elevations to get in on the snow action. Snow levels look to remain above mid elevation areas ( >6500-7000'), but could come down a bit lower across the far northern portions of the state. In general, Utah forecasted to only get a kiss from this AR event, with the Utah/Idaho border area getting the most precipitation. Central Wasatch areas - Cottonwoods - currently look to get meager pickings in terms of liquid/snow. 

ECMWF 06Z 10/24/2025 Ensemble Total Snow Accumulation at Alta, UT

It's very likely that details of this forecast will continue to shift, so it is difficult to put numbers on precip and snow amounts this weekend. But for the sake of curiosity, let's look at the ensembles - collection of multiple model runs with slightly varying input conditions - for Alta, UT. Essentially, the ensembles spell out a bit of a bleak future in terms of snow for the upper central Wasatch, with a few inches of snow late Saturday into Sunday/Monday the most likely solution at the moment. 

Beyond

While Utah will likely miss out on the AR party this weekend, the flood gates will open for the PNW with a wave train of multiple systems moving into the region through the middle of next workweek. Utah may get a bit more energy and moisture from one of these systems late Sunday into Monday, but not expecting anything super significant. I think the more interesting thing is if this storm squeezes out enough liquid to help SLC break 5" total precipitation for the month of October. As of now, KSLC sits at 4.95" which already smashes the old monthly record. Just need a little more...

ECMWF Extended Ensemble 00Z 10/23/2025: 7-Day Precipitation anomalies Oct. 23-Nov. 1

It's difficult to say what will happen beyond early next week, but there are hints that a decent period of ridging accompanied by dry and relatively warm weather will settle in across the Great Basin and Utah the middle of next week through the first week of November. So looking like warmvember to start... 

ECMWF Extended Ensemble 00Z 10/23/2025: 7-Day 500 mb gph anomalies Oct. 31-Nov. 7