textproduct: Salt Lake City

KEY MESSAGES

- Widespread south-southwest winds in excess of 40 mph and up to 55 mph will develop this afternoon, with the strongest winds expected to occur on Monday night as a cold front passes through. Elevated winds will persist thereafter through Wednesday.

- Expect broadly 1-2 feet of mountain snow through Wednesday, with two periods of heavy snowfall: overnight tonight and mid-day Wednesday as a couple of cold front push through the area.

- While most valleys will transition to snow by mid-day Tuesday, precipitation will be at a relative lull by that point. As precipitation ramps back up early Wednesday, valleys will likely receive minor snow accumulations through the day, around 2-4 inches along the Wasatch Front with locally higher amounts on benches (and in Cedar City).

DISCUSSION

Breezy southerly to southwesterly winds around 45-55 mph are noted along ridgelines early this morning, indicative of overall increasing southerly flow ahead of our first storm system moving through overnight tonight. To give a brief overview of the next few days, we're looking at two main storm systems that will each bring a shot of cold air and period of heavy mountain snowfall as they pass across Utah and southwest Wyoming, accompanied by persistent strong winds through Wednesday. Additionally, although the dynamics with these two systems are quite impressive, moisture only peaks around 150-200% of normal near the times of the frontal passages...otherwise hovering around normal.

The first system will swing through the region tonight, with 700-mb winds peaking late evening as a 180kt jet continues to develop across CA-AZ. Models still disagree on the exact magnitude of these winds, but trends have overall increased, with the GFS/NAM/HREF suggests 65-70kt winds at 700-mb. Although synoptic winds peak after sunset, surface wind gusts will reach 45-55 mph in many locations. Some areas that are downwind of higher terrain could even exceed 55 mph at times (e.g. Tooele, Salt Lake Valleys where this is prone to happening). Additionally, with drier low levels, precipitation onset later in the evening could help mix those strong winds to the surface, particularly across southern Utah. In the aforementioned downslope areas, precipitation onset may be delayed as precipitation evaporates before reaching the ground.

Along with winds, expect a relatively short period of heavy mountain snowfall along this frontal passage, especially across southwest Utah. For example, downscaled guidance at Brian Head suggests 7-10 inches of snow will fall in 6 hours between 11PM-5AM...with the HREF mean even suggesting a few hours of 2.5 inch per hour rates. Other high-res guidance also favors periods of snowfall rates in excess of 1 inch per hour in other higher terrain areas.

Following the passage of this first system, snow levels will continue to fall, though valley precipitation will lighten up considerably during the day Tuesday. Orographic showers will continue in the mountains. As upper-level diffluence strengthens ahead of the second system, precipitation will start to increase once again Tuesday night. A strong cold front will push through the area mid-day Wednesday, bringing another period of heavy mountain snowfall, a transition to westerly or northwesterly winds, and a shot of colder air as 700-mb temperatures drop to -15C or so. Lake-effect remains possible Wednesday night, though chances are fairly low (around 20%).

While mountain and Wasatch Back snow totals looks relatively impressive (broadly 1-2 feet over 3 days), valley snow totals are fairly low owing to somewhat limited moisture. Many valleys can expect largely 2-4 inches, with higher amounts on benches and near Cedar City. Most of this snow will fall on Wednesday. Totals could be boosted, however, if favorable mesoscale details pan out like some model guidance suggests. Modest instability on Wednesday ahead of the front could result in heavier snowfall with the frontal passage, but will need to monitor as higher-res guidance comes in.

Orographic showers will continue into Wednesday night, with showers slowly tapering off into Thursday. The pattern looks to remain relatively active with a potential trailing wave on Friday, then high pressure temporarily building over the weekend.

REST OF UTAH AND SOUTHWEST WYOMING

Gusty winds from the south to southwest will last through the day. Gusts around 25 knots are likely by 16Z for much of Utah, with gusts around 40 knots for southwest Wyoming, western Utah, and for valleys with downslope enhancement from the south or southwest. Clouds will increase as a storm system approaches, with scattered to broken clouds in VFR range transitioning to overcast around 00Z. Scattered light rain and snow showers will be capable of enhancing wind speeds and altering directions after 03Z. The boundary will result in low level wind shear for southwest Wyoming and much of Utah.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Wind Advisory from 11 AM this morning to 5 AM MST Tuesday for UTZ101-102-115-116-122-127.

Wind Advisory from 8 PM this evening to 5 AM MST Tuesday for UTZ105-121-128>130.

Winter Storm Warning from 5 PM this afternoon to 5 AM MST Thursday for UTZ108-110>112.

Winter Weather Advisory from 5 PM this afternoon to 5 AM MST Thursday for UTZ113-117.

Winter Storm Warning from 5 PM this afternoon to 5 PM MST Wednesday for UTZ125.

WY...None.