textproduct: Salt Lake City

KEY MESSAGES

- Building high pressure keeps conditions dry and mild through the weekend.

- A cold front will bring valley rainfall and mountain snowfall beginning as early as Monday evening. A second system looks to push in Wednesday bringing more notable accumulations to our mountains.

- A shift to a cooler and unstable pattern will follow for the majority of next week.

DISCUSSION

Per mesoanalysis, height rises are currently occurring with a building upper ridge across the northern Great Basin. This will generally yield mild and dry conditions through the weekend with temperatures running 10 to 15 degrees above average.

Come Sunday evening into Monday morning, a shortwave trough will push into the Pacific NW with diffluence beginning to overspread much of UT by Monday afternoon. An associated cold front will begin to push into northern UT in the morning hours, slowly moving southeast through the afternoon hours. The front is expected to weaken with its trek south as more favorable forcing aloft moves off to the northeast with the trough ejection resulting in less precipitation with southern extent with most accumulating precipitation favoring terrain. For example, the probability of 24hr precipitation greater than 0.10" through Tuesday morning generally ranges from 10-30% along much of the Wasatch Front with higher terrain ranging from 70-90%, with the higher bounds of both ranges lying along the northernmost portions of UT. Additionally, snowfall amounts along higher terrain will not be overly robust as the probabilities for greater than an inch generally ranges from 20-40% across most of the Wasatch front with the Bear River Range ranging from 50-70% due to better forcing up north.

The cold front is then expected to stall across northern UT, perhaps moving north somewhat as a warm front on Tuesday before eventually diving south once again as a cold front later in the week. At the same time, a longwave trough will begin progressing inland along the central CA coastline Tuesday afternoon with ample diffluence ahead of it, gradually spreading over UT throughout the afternoon. As such, ascent will begin to increase throughout the afternoon and, with the front in place, yield higher precipitation rates along northern UT. Additionally, PoPs will begin to increase across the CWA as large scale ascent continues to increase into Wednesday as the trough axis pushes toward the western Great Basin. This system arrives with more favorable dynamics and quality moisture, resulting in roughly a 40-70% chance of at least 0.10" accumulating along the I-15 corridor throughout UT over a 24 period from Tuesday evening through Wednesday evening, with the higher bound of the range favored with northern extent. Higher terrain across the state generally ranges from 70-80% of 0.10" of water or greater through this period as well. As it stands, there is a 60-80% chance of 6" of snow or greater across the Bear River Range and the Upper Cottonwoods from Tuesday morning through Thursday morning.

Unfortunately, it does appear that our valley snow drought at KSLC will persist with temperatures remaining a tad too warm given the nature of decaying atmospheric rivers. For the majority of valleys along the Wasatch Front, there is roughly a 15-25% chance of exceeding 0.10" of snow through a 72hr period Monday through Wednesday. Chances do increase along the benches Wednesday night into Thursday morning as a weak shortwave brings another round of snow, though this generally ranges from 30-50% of 0.10" or greater.

A brief lull may exist Friday and Saturday as transient ridging appears to build in following the departure of the longwave trough. Ensemble cluster analysis continues to indicate that the unstable pattern will continue into next week, now with ~85% of all ensemble guidance favoring lower geopotential heights south of CA. While amplitude and timing still show some disagreement, it does appear that the extended forecast possesses even more chances for precipitation across the forecast area.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will prevail through the period with terrain driven winds at all TAF sites.

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SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...None.