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FXUS65 KSLC 012300 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 400 PM MST Fri Dec 1 2023

SYNOPSIS
A series of storm systems will impact the area through early Monday, bringing signficiant mountain snow, especially for northern Utah. High pressure is expected to return to start the upcoming work week.

.SHORT TERM (Through 12Z/5AM Monday)...Early Friday afternoon, an elongated, north-south oriented shortwave trough was migrating eastward across northern and central Utah. This trough is responsible for the band of snowfall currently moving across the area. This snow has largely ended in valley locations as of 3PM MST. Subsidence in the wake of this trough will allow for a lull in precipitation for valleys for the remainder of the afternoon and early evening, while rates diminish in the mountains but light snow continues. This break will be short-lived, however, as the next shortwave can be seen moving through SW Idaho and northern Nevada. Snowfall associated with this wave will spread east- southeast across northern Utah this evening, generally between 7PM-9PM. Valley snow associated with this wave will begin to taper off shortly after midnight while snow continues in the mountains.

A third and final wave will be on the doorstep by mid-afternoon Saturday. This wave will be the strongest in terms of lift, wind and will contain the most moisture. This wave will also usher in stout warm advection which will force a gradual rise in snow levels.
Valley snow associated with this wave will begin generally between 3PM-5PM, and precipitation associated with this wave will largely continue through Sunday night. The late Saturday evening through mid- morning Sunday period is particularly favored for heavy snow and strong winds across northern Utah's mountains, especially across the Wasatch Mountains, Wasatch Plateau and Bear River Range. During this time, wind gusts in the 45-55 mph range are likely for exposed ridgelines (with locally stronger gusts) as well as across Uinta County, WY. The combination of heavy snow and strong winds will create hazardous winter conditions for mountain passes. In valleys, snow is expected to gradually mix with and change over to rain. In the Salt Lake Valley as an example, precipitation type probabilities favor mainly all snow (with a 90% or greater probability) through late Saturday afternoon, when a rain/snow mix begins to be favored. Finally, by early Sunday morning, just after midnight, mainly rain is favored (generally >80% probability), and these probabilities remain unchanged for the remainder of the event. For Provo, the trends are similar, with a slightly later transition to rain favored. For Ogden, again similar trends with a changeover to rain favored by just before sunrise Sunday morning. For the Cache Valley, rain is favored here as well, but not until Sunday afternoon when probabilities for rain reach 80% and probabilities for snow drop to 20%. In terms of snow levels, they will begin at valley floors and raise to 6,000 (25th percentile) to 7,000 feet (75th percentile) by Sunday afternoon. See WSW products or weather.gov/slc/winter for the latest snow accumulations.

Winter driving conditions are expected across summits like Logan, Soldier, Parleys and Sardine through the period, with worst impacts associated with the windows of heavier snow and wind, especially in that late Saturday night through mid-morning Sunday period. In valleys, impactful winter driving conditions will be tied to periods of heavier snowfall combined with overnight periods such as this evening and late Saturday afternoon/evening.
With this being the first accumulating snow of the season for many, remember to reduce speeds, increase following distances and ensure your vehicle's tires have sufficient tread and is in good working order.

.LONG TERM (After 12Z/5AM Monday)...The extended forecast period brings the tail end of the winter storm affecting the CWA followed by mean ridging and warming. Subsidence aloft with the ridging overhead will promote valley inversions back for the work week.
Slight potential for a northerly passing shortwave to bring some relief and mixing but the best chance comes by the end of the work week when the next extensive trough pattern looks to bring another win storm.

As the weekend storm exits the area its likely we keep some clouds and lingering snow showers over the high terrain of northern and even central Utah on Monday. Some light snow could fall during the morning and afternoon but likely adding no more than trace to minimal accumulations. Subsidence builds and we clear out skies over the first half of the work week as inversions build through at least Wednesday. Forecasted highs reach the low 40s along the Wasatch Front but inversions could keep that down while the higher terrain see the bulk of the warming trend.

Models are beginning to lean towards the next winter storm being pushed later in the week with a late Thursday into Friday start being the earliest arrival. Deterministic models grow a rather extensive trough pattern with strong cooling aloft that would drive statewide impacts for the storm into the weekend.

AVIATION
KSLC...A break in snow with VFR conditions and mountain obscuration will persist until ~02Z before light snow returns with MVFR conditions as CIGs and VIS drop. Confidence is increasing that heavier snow arrives ~05-06Z lowering categories to IFR for a couple of hours. This will then be followed by another break in snow with a return to VFR conditions until after 12Z. Winds will be light and variable.

REST OF UTAH AND SOUTHWEST WYOMING
The southern half of the airspace will remain VFR as snow pushes out of the area. Mountain obscuration will persist as CIGs remain below crest level. The northern half of the airspace will see a break in snow until ~02Z as light snow moves back in followed by moderate snow closer to 06Z.
This will lead to MVFR/IFR conditions and mountain obscuration. Snow will taper after 08Z before another return after 12Z. Winds will generally be out of the west and gusty across far northern and western Utah as well as along and east of the Wasatch/central mountains.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Winter Weather Advisory until 11 AM MST Sunday for UTZ103-104- 107-109.

Winter Weather Advisory until 5 AM MST Sunday for UTZ105-106-113- 117.

Winter Storm Warning until 5 PM MST Sunday for UTZ108.

Winter Storm Warning until 5 AM MST Monday for UTZ110-111.

Winter Weather Advisory until 5 AM MST Monday for UTZ112.

WY...None.

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