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FXUS65 KSLC 082206 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 306 PM MST Fri Dec 8 2023

SYNOPSIS
A winter storm will gradually end this evening across northern and central Utah. The weather pattern will stay progressive, with additional weak but mostly dry disturbances expected to impact Utah into early next week.

.SHORT TERM (Through 12Z Sunday)...A very cold upper level trough will continue to shift east into Wyoming and Colorado through the evening. With very cold 500mb temperatures (~-34C across northern Utah), steep lapse rates are supporting convective development across northern Utah. A dry surface layer is inhibiting much surface impacts for the valleys. Accumulating snow is occurring with orographic enhancement over the Wasatch Mountains.

Expect the potential for a brief window of lake effect snow, however, the dry low levels may inhibit much impact to the valleys given the transitory nature and the time that would be needed to saturate. Based on flow and much of the CAMS, the initial band may favor southeastern Salt Lake County, transitioning to western Salt Lake County and potentially Tooele Valley before ending between 9 and 11 PM. While the NAM Nest continues the lake effect band into the overnight hours, model soundings suggest the NAM Nest (and NAM) are underestimating the dry low levels.

Upper level ridging will gradually shift into the area Saturday into early Sunday. Very cold temperatures can be expected, with wind chills falling to the teens to single digits across the northern valleys by Saturday morning.

One thing to note, an area of deep convection is currently near Neola. Webcams suggest this may bring a brief period of heavy snow if this feature holds together toward Roosevelt and Altamont.

.LONG TERM (After 12Z Sunday)...Unsettled northwest flow will be in place for the first half of the extended period. An atmospheric river will be making landfall and pushing its moisture further into the Great Basin region through Monday. This moisture will creep into northern Utah and allow for some slight chances of precipitation. There will also be a couple of shortwave troughs that are expected to move through during the early portions of next week. With all this being said, there is not expected to be much in the way of great synoptic lift for a lot of precipitation to occur. Most of the precipitation chances with these system will most likely be orographically enhanced due to these conditions.
Minimal accumulation is expected with these storms.

The second shortwave that arrives on Tuesday will be slightly stronger than the previous shortwave and allow for moisture to be pushed further south and allow some slight chances of precipitation into the central Utah mountains. Temperatures with this shortwave will dip slightly but still stay relatively close to seasonal normals.

What happens after these shortwaves is largely uncertain.
Guidance is currently split on whether the second shortwave becomes closed off or not and then what that evolution would look like. There currently is not much in the way of potential moisture but with a closed low overhead or near the area, the synoptic lift would be there to help higher terrain locations receive some orographically enhanced precipitation. This is will be something to continue to monitor as guidance hones in on the evolution of this potential closed low.

AVIATION
KSLC...VFR conditions will prevail over the KSLC terminal with periods of mid-to-high end MVFR conditions in passing snow showers through roughly 03Z. CIGs will remain at, or below, 6kft AGL through the evening hours and will dissipate through the overnight hours. Otherwise, northwest winds will remain in place through the evening and overnight hours, transitioning to southerly flow around 13-14Z.

REST OF UTAH AND SOUTHWEST WYOMING
Terrain driven snow showers will prevail across the northern half of Utah and southwest Wyoming through the remainder of the evening, decreasing in coverage overnight. MVFR to IFR conditions will be found in these showers, especially on the Wasatch Back through the remainder of the daytime hours. CIGs around 6-7kft AGL will create local mountain obscuration, primarily across the northern third of the area. Otherwise, clouds will gradually clear overnight.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Winter Weather Advisory until 11 PM MST this evening for UTZ108- 112-113-117.

Winter Storm Warning until 11 PM MST this evening for UTZ110-111.

WY...None.

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