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FXUS65 KSLC 052246 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 346 PM MST Tue Dec 5 2023

SYNOPSIS
High pressure will continue to build into the region today. Another series of storm systems lines up for the second half of the week.

.SHORT TERM (Through 00Z Friday)...High pressure will continue to be over the Great Basin area through Wednesday. Mostly clear skies are expected for the overnight period. Some areas of fog are possible in some northern valleys, especially in the Cache Valley. Haze will also be possible on Wednesday, particularly in the Wasatch Front and the Uinta Basin. The axis of the ridge will move through overnight and as a result, southwest flow will increase Wednesday. This will increase wind speeds at the surface as 700mb flow is between 20kts and 35kts. Wind gusts with this flow could reach up to 30 mph in some areas. There is a caveat to these gusty winds reaching lower elevation valleys though and that is valley inversions. These inversions will inhibit mixing and not allow the gusty winds to reach the surface.

Heading into Thursday, the first storm system moves into Utah.
This shortwave is expected to graze northern Utah. Rain is expected for most low elevation valleys as snow levels with this storm will be between 5500t and 6500ft. The most significant snow is expected to fall in areas above 6500ft, where 2" to 4" will be possible by the end of the day Thursday. Even though not much precipitation is expected from this event, the cooling aloft should allow for valley inversions to weaken on Thursday.

.LONG TERM (After 00Z Friday)...Our most impactful wave of this series of shortwaves remains on track for Friday morning. Before we get to that period though, northern Utah valleys are first expected to experience a period of rain Thursday evening, transition into a rain/snow mix overnight and become snow by Friday morning. From Thursday evening into the overnight hours, look for moisture to begin spreading southward and just about encompass the state with just the St. George vicinity and Glen Canyon vicinities remaining dry. That stated, even Glen Canyon will see some showers by daylight Friday. The range of possible snowfall amounts in our mountains for Friday is still showing quite the range. For example, the NBM range of potential snowfall in 24 hours for Alta is anywhere from 5 to 30 inches, not much certainty at all. Keep in mind, that's a 24 hour range of uncertainty and not the storm total. Looking at what the EPS and GEFS forecast has, they have come into much better agreement compared to yesterday and thus keep AR moisture well away from Utah Friday. We will definitely need some higher resolution guidance to help us get the appropriate snowfall amounts forecasts Friday.

Increasing statewide northwest winds remain in the forecast for Friday. The primary impact here will be blowing snow at ridgetop level across the central Utah mountains and possibly at some of the summits and higher elevation passes along I-70 like Salina Summit.
At the moment, winds at valley level are expected to remain below advisory or high wind criteria but this will be something to monitor in the coming days for areas like Castle Country.

Our forecast for the weekend has not changed all too much. Saturday remains a fairly dry day though there may be lingering showers in the morning before conditions exit. Our third wave in this ongoing on again off again pattern of precipitation remains forecast for Sunday across northern Utah. There are still questions regarding how far south moisture will extend and how much moisture will be available. IVT moisture remains elevated but has decreased in its potential for Sunday for our area. Favored moisture is currently further north and northwest.

Headed into next week, milder conditions are anticipated with seasonal conditions. What could put a wrench in the weather flow early next week is a potential shortwave trough on a quick trajectory through the Intermountain West. At the moment, about 30% of ensemble solutions favor a more substantial impact to Utah while just about all of them favor some of influence into the weather pattern. Essentially, this should keep our temperatures seasonal but the question will be how much, if any, precipitation decides to fall as a result of the trough.

AVIATION
KSLC...Northwesterly winds are expected to transition to light and southeasterly around 03-04z. Overnight, there is a <10% chance of low stratus development between 09-15z. Otherwise, expect clear skies and VFR conditions. Additionally, there is a 30% chance that winds remain southerly on Wednesday afternoon.

REST OF UTAH AND SOUTHWEST WYOMING
Light winds and VFR conditions will prevail for most locations. Areas that may see overnight fog development include KLGU (75% chance) and KHCR (30% chance).

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

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