textproduct: Salt Lake City

KEY MESSAGES

- Winds continue to increase out of the south-southwest today through Wednesday with the strongest winds in this stretch expected to occur on Tuesday as a cold front passes through.

- Multiple chances for accumulating mountain snowfall exist this week, with the Tuesday night through Thursday system bringing significant snowfall to the majority of our mountains.

- The threat for valley snow continues to increase with the Tuesday night through Thursday system for nearly all valley locations with the exception of lower Washington county.

DISCUSSION

Southwesterly winds continue to increase across the forecast area this afternoon as a longwave trough continues to deepen off the southwestern CA coastline. Winds will remain elevated through Wednesday as this trough strengthens and ejects off to the northeast. On Tuesday, 700mb flow will strengthen markedly as the base of the trough ejects across northern UT with an associated cold front racing across the area in the afternoon hours. As this occurs, gusts across the West Desert and the Tooele Valley could reach as high as 55mph as the elevated winds aloft mix down to the surface. Fortunately, for the Wasatch Front, the probability of gusts 45mph or greater (criteria for a Wind Advisory) is generally 20% or less at this time as the cold front swings through. While conditions are expected to be blustery across the Wasatch Front over the next few days and perhaps see a few instances of gusts 45mph or greater, widespread impacts are not expected at this time.

Strengthening large scale ascent aloft as diffluence overspreads the area through Monday will begin to overlap with increasingly robust moisture advection late Monday afternoon resulting in notable PoP increases across the entire forecast area. Within this warm and moist southwesterly flow regime, we can expect the majority of our valleys to remain socked in with rainfall with only our high terrain seeing snowfall given snow levels remain generally above 5000ft through Tuesday morning. Additionally, the Salt Lake Valley and Tooele Valley may see less rainfall from this event compared to surrounding areas as downsloping may occur, keeping rainfall totals modest. For example, there is roughly a 30-60% chance of the Salt Lake Valley and Tooele valley seeing 0.10" of rainfall or greater across a 24hr period ending Tuesday morning compared to a roughly 70% chance or greater along the northern Wasatch Front and southern UT I-15 corridor. Lastly, given some elevated instability existing within the thermodynamic profiles Tuesday afternoon, storms and snow showers ahead of and along the cold front may produce isolated lightning.

Following the departure of the first trough and associated frontal passage Tuesday morning, a brief lull will settle in ahead of our second trough as large scale subsidence builds in temporarily. During this time, much colder air aloft will begin to advect into the area (700mb temperatures potentially as low as -8C to -10C by Wednesday morning) which will drop snow levels to around 4000ft ahead of the incoming system. 700mb temperatures will continue to drop throughout Wednesday with snow levels reacting accordingly, dropping below 3000ft by Wednesday evening. By this point, we can assume that valley snow across just about the entirety of the forecast area (except for St. George) is a given at this point. Amounts have trended up for most of the valleys along the Wasatch Front with around 1-5" expected for the lower elevations with potentially as high as a foot across the eastern benches. Cedar City is also favored within this regime, with a range of 7-11" of snowfall accumulations possible.

Prolonged northwest winds associated with the second system will create an extremely favorable environment across most of our mountains for significant accumulating snowfall, with a strong emphasis on the Bear River Range and the Upper Cottonwoods. Additionally, while not necessarily favored within a northwest flow regime, the Tushars and Brian Head will also see notable accumulations from this system as stronger ascent overhead is forecast to linger with southern UT remaining in close proximity to the trough axis. Across all the specific locations listed above, amounts up to 2 feet are expected with accumulations across the Upper Cottonwoods potentially exceeding 3 feet.

As we enter Friday, a couple lingering shortwaves will continue to progress into the forecast area bringing continued isolated snow showers to northern UT. Ascent has trended somewhat stronger with todays guidance with slightly more moisture lingering, increasing snowfall accumulations on Friday both across most mountains and valley locations. Ample uncertainty exists regarding Friday at this time, and amounts will be ironed out as we draw closer.

Ridging appears to build back in as we enter the weekend, though it remains uncertain with how long this will remain in place for. Looking into the long range, ensemble cluster analysis does indicate that the active period may continue with large scale western troughing as a common solution among most members.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will prevail across the area through Monday afternoon with CIGS remaining above 15 kft. Winds will remain generally southerly through tonight, with south winds strengthening and becoming gusty Monday morning. Gusts in excess of 30 KTS can be expected at terminals along and south of I-80 Monday afternoon.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Wind Advisory from 11 AM Monday to 5 AM MST Tuesday for UTZ101- 102-115-122.

Winter Storm Watch from Monday afternoon through late Wednesday night for UTZ108-110>112.

Winter Storm Watch from Monday afternoon through Wednesday afternoon for UTZ125.

WY...None.