textproduct: Salt Lake City

KEY MESSAGES

- Ridging continues through Monday bringing record breaking warmth and dry conditions to the forecast area.

- A pattern shift is expected to develop Tuesday bringing wetter and cooler temperatures to the forecast area through at least Thursday.

- A prolonged valley rainfall and mountain snowfall event looks to continue from as early as late Tuesday into Friday. Additionally, gusty conditions will develop Wednesday and Thursday as a system moves into the region.

DISCUSSION

Current satellite imagery indicates dry low levels with modest moisture continuing to stream in along the western periphery of a mid/upper level ridge. Primarily light upper level cloud cover will continue to stream in from the southwest across the region today enabling ample surface mixing to occur. With just enough mid-level moisture in place, some high based showers with potentially a few rumbles of thunder are possible across the West Desert this afternoon as a weak midlevel trough progresses through the area. Given the aforementioned dry low levels and warm temperatures this afternoon, inverted-v thermal profiles are abundant across hi-res guidance yielding DCAPE ranging from roughly 600-900J/kg, increasing with eastern extent. Given weak shear and lack of daylight, storms will quickly die off around 6-7PM as temperatures begin to cool along the easternmost edge of Box Elder and Tooele counties. The main threat with these storms will be strong gusts to around 40-50mph and occasional lightning.

On Sunday, precipitation chances have decreased somewhat as mid- level ascent has weakened across guidance with lower moisture quality. If at all, afternoon storms would remain highly isolated across the higher terrain of Utah. On Monday, somewhat higher quality mid-level moisture will begin streaming in along the southern stream increasing PoPs to roughly 20% across northern and central UT high terrain in the afternoon. Come the evening hours, increasing mid-upper level moisture arrives as a shortwave trough within the northern stream swings down and phases into the southern stream. This will serve to increase ascent ahead of the shortwave keeping PoPs elevated across northern UT Monday evening into Tuesday afternoon.

High confidence remains regarding a pattern shift Tuesday, persisting through the end of the work week resulting in cooler and wetter conditions across the region. The aforementioned shortwave trough embedded within the southern stream will traverse across UT with an associated cold front in the morning hours Tuesday. Ample moisture will continue streaming in ahead of the frontal boundary, moistening the PBL and increasing PoPs increasing for most lower elevation locations across N and central UT as well as SW WY to around 30-60% Tuesday afternoon. Higher terrain will see chances for precipitation increase to around 60-80% with orographic influence and higher quality mid-level moisture pushing into the region. Given preceding warm conditions, snow levels will generally remain above 7000ft as this frontal boundary arrives keeping most areas socked in with rain other than the Upper Cottonwoods, Bear River Range, and High Uintas, where a mix of snow and rain is expected. Snow levels then increase to 8000-8500ft late Tuesday evening as warm and moist southerly flow takes control once again allowing more rain to mix in across higher elevation locations.

A brief lull is forecast to develop late Tuesday morning through late Tuesday evening as subsidence builds in behind the frontal feature. Some residual moisture aloft will linger with enhanced flow aloft, providing enough ascent to keep scattered showers in play for through the aforementioned timeframe with PoPs generally hovering around 40-60%.

Beginning early Wednesday morning, guidance continues to indicate a complex system moving into the Great Basin. Initially, a few weak impulses will dive southeast from the main trough up towards the PNW and traverse across northern UT. These features will provide ample ascent and assist in drawing in deeper moisture from the southern stream. PoPs will continue to increase markedly as the trough deepens and dives SE toward the area Wednesday with the West Desert, southwest UT, and southeast UT generally seeing PoPs around 30-60%, the I-15 corridor and SW WY ranging from 60-80%, and high terrain locations seeing 80%+. Most locations can expect precipitation in the form of rainfall as this initial push will remain quite warm, keeping snow levels around 8000-8500ft into Thursday morning ahead of a cold front. Following the passage of another cold front later Thursday morning, snow levels will drop to around 5000-6000ft throughout the afternoon Thursday as colder air pushes in via northwesterly flow. Snow levels will then continue to drop to as low as 4000-4500ft throughout Friday morning into the afternoon hours. Some questions remain, particularly regarding potential subsidence building in and precipitation rates as this would typically favor valley snow earlier this season, or any other regular season for that matter. As it currently stands, NBM probabilities for 0.1" of snowfall along the valley floors of the I-15 corridor of northern and central UT range from 30-50%. This will, however, absolutely change as the event draws closer. Given preceding warm surface temperatures and potential subsidence behind the front, only modest accumulations appear likely at this time, if at all.

The pattern looks to remain active as we head into the weekend, though considerable uncertainty remains regarding placement and evolution of other waves that look to propagate east from the Pacific. Regardless, wet and cool conditions appear likely to continue past the long-term forecast period.

REST OF UTAH AND SOUTHWEST WYOMING

Most areas will see breezy southwesterly to westerly winds this afternoon up to around 20-25kts before lighter, terrain-driven winds prevail after around 01-03z or so. Relatively weak high-based showers/virga could produce gusty and erratic winds, mainly across an area between KENV-KDTA-KSVR-KHCR between 21-04z as they move from west to east. Expect wind gusts of up to 25-35kts at times, though there is a 10% chance that winds reach up to 45kts in a couple isolated areas. BKN mid-level clouds will persist through the evening with VFR conditions prevailing.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...Red Flag Warning until 9 PM MDT Monday for WYZ277.