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FXUS65 KSLC 292248 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 348 PM MST Wed Nov 29 2023

SYNOPSIS
Cold but mild conditions are forecast for most through tomorrow while an area of low pressure to our south may bring isolated snow showers to the mountains. Several waves of moisture will provide snow showers Friday through Sunday with rain showers mixing in Monday.

.SHORT TERM (Through 12z Friday)...Pesky low stratus deck continues to hang out across the Great Salt Lake/West Desert/Dugway Proving Ground area even into these mid-afternoon hours. Mid to upper level clouds are beginning to evade southern Utah associated with an area of low pressure centered further south. This low may push enough moisture northward into Utah to allow for isolated snow showers tonight along the terrain.
Similar temperatures are forecast for tomorrow when compared to today though perhaps a few degrees cooler for some. Essentially we're just splitting hairs with the forecast though, cold is cold and it'll be cold again tomorrow. Additional snow showers become less likely as we go through the day Thursday and into the evening.

.LONG TERM (After 12Z Friday)...A beneficial (early-winter)
unsettled period remains poised to begin Friday, lasting potentially more often than not through much of the weekend across central and namely northern portions of the forecast area.
Several shearing short wave troughs attendant with a a strong pacific jet are expected to translate across the northern Great Basin region and into the local area, with the first of these crossing the region Friday.

P-type is a non-issue, at least initially, as vertical profiles are in full support of snow to valley levels beginning Friday.
Dynamically, the shearing nature of the initial short wave Friday, and second trailing Friday night into Saturday, owes to modest at best large-scale ascent however. This due to largely weak thermal packing within CAA/axis passages through the first 24-36hr period, modest W-NW flow (in general), but a somewhat favorable left entrance region of the upper jet over northern NV should aid.
Orographic enhancement for favored west-northwest terrain does look descent across the north though, given deep layer moisture advecting into the region coupled with increasingly favorable low/mid level lapse rates in time. Likely advisory level snow amounts/impacts for northern valleys and mountains spread over time through Saturday, and looking at the first potential for a wider scale accumulation potential on road surfaces to valley levels...especially later Friday through Saturday morning. Will continue to coordinate w/UDOT on this potential moving forward.

Uncertainty in the forecast increases significantly after Saturday however, with latest trends in deterministic/ensemble guidance trending towards a further north translation of short wave energy, and IVT of remnant atmospheric moisture, during the Sat night-Sun night timeframe. Further south solutions of this short wave energy/IVT remain though. Although indications of the Great basin becoming more ridge dominated exist, with much of the forecast region phasing into a more stable anticyclonic northwest flow with the jet phasing north/east of the area Sunday on, its not set in stone and northern Utah could still see a productive precip event within strong WAA coupled with the inland penetrating IVT. The latter would decrease snow ratios significantly coupled with a thump of additional water, and introduce valley p-type challenges as many would phase more towards rain vs. snow. Time will tell, and these details will begin to fall out in time moving forward. Leaning more towards the northern solutions/less precip however.

Here's where the positives of the unsettled period end though. Prep for a return of building valley inversions early-late next week as high confidence exists that the upstream ridge will amplify and shift overhead during this period. H7 temps pushing +4 or +5 are likely to be realized by Wednesday within a strongly subsident environment...a substantial cap! Likely to see more stratus trapped as well given the set up from the weekend...

AVIATION
KSLC...MVFR conditions are likely to occur through the TAF period. This is mostly due to the inversion conditions that are present in northern Utah valleys. VIS will likely stay between 3SM and 5SM for most of the period. For the overnight conditions, there is a 40% chance that IFR conditions resume and a 20% chance that LIFR conditions occur. MVFR conditions should resume by early afternoon Thursday. CIGS will stay around 8kft through the period.
Light northwest winds are expected to switch to light southeast winds between 05Z and 07Z. There is a 30% chance that the light northwest winds persist through the night.

REST OF UTAH AND SOUTHWEST WYOMING
Light and diurnal winds expected through the TAF period. Inversions will remain in place and cause VIS to go down ~5SM for areas along the Wasatch Front. Some areas may see lowered VIS and lowered CIGS, due to low stratus clouds, especially in northwestern Utah, along the Wasatch Front, and in the Uinta Basin. VFR conditions are likely in most areas that don't experience inversion conditions. Some precipitation will occur in far southern Utah, especially by Lake Powell during the overnight period.

SLC WATCHES/WARNINGS/ADVISORIES
UT...None.
WY...None.

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