textproduct: Salt Lake City

KEY MESSAGES

- Widespread south-southwest winds in excess of 45 mph and locally in excess of 60 mph will continue through the night, with the strongest winds expected to occur late this evening and overnight behind a cold front. 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 on 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, with widespread 1-4 inches with locally higher amounts on benches and in Cedar City.

DISCUSSION

The large-scale pattern this afternoon depicts a closed low off the central California coast gradually filling and beginning to eject inland as another closed low continues to slide down the BritCol Coast. Ahead of these storms, southwesterly flow is increasing across the Intermountain West, with H7 winds over Utah this afternoon in excess of 40 kt. Meanwhile, moisture associated with a landfalling atmospheric river is rotating around the southernmost storm and spreading into the desert southwest. This moisture is associated with IVT anomalies in excess of the 99th percentile of climatology for this time of year.

As the southern trough ejects across Utah tonight, a cold front will push into Utah from the west-southwest. This will increase the southerly surface pressure gradient, and coupled with H7 flow of 50-65 kt, it is anticipated that winds later this evening and overnight will be stronger than what winds have been this afternoon (which already reached 40+ mph across a number of western and central Utah sites). Have upgraded the Wind Advisories to High Wind Warnings across the northwest deserts and the Tooele Valley and added Wind Advisories for additional zones. Would not be surprised if additional areas reach Warning criteria (gusts to 58 mph) as HREF probabilities show portions of west-central Utah with a 40-55% chance of reaching criteria. However, the HREF in general tends to be a bit overdone with winds.

Precipitation associated with the storm will begin filling in across southwest Utah this evening, then spread north and east through the late evening and overnight hours. Snow levels will begin fairly high given the mild antecedent airmass. However, snow levels will fall pretty quickly behind the front. The front itself will be moving very quickly. As such, precipitation along the frontal band is not expected to last more than 2-4 hours and as such, valley snow will be very limited. Lingering orographics will then continue to generate precipitation over/near the northern and southwest Utah mountains into tomorrow. Most mountains are expected to see around 4-10 inches (25th-75th percentile of the NBM) tonight through tomorrow, with locally up to 15 inches possible in the upper Cottonwoods, high Uintas, Bear River Range, the Tushars and near Brian Head.

The northern storm arriving on Wednesday will bring the best chance of widespread snow across the area, including in the valleys given the colder airmass associated with it. Ahead of this storm, southwest flow will increase across the area again by late Tuesday afternoon. Precipitation will increase late Tuesday night/Wednesday morning, heaviest late morning through late afternoon as the associated cold front crosses the area. Lingering orographics will then favor west to northwest aspects through early Thursday morning. The northern and southwest Utah mountains have a 60-100% chance of at least 12 inches of snow with this storm. Many valleys (not including Lower Washington County and the Lake Powell area) have at least a 70% chance of 2 inches of snow or greater, although chances drop to less than 40% for 4 inches or greater. The exception is the benches and along the I-15 corridor where this is more likely. Given that this will likely be the biggest valley snowstorm overall this winter (it's all relative), winter weather highlights may be necessary for at least some valley zones. Will evaluate this need on upcoming shifts.

Precipitation will wind down through the morning hours on Thursday. However, the break looks to be brief, as another storm looks increasingly likely for Friday. Even so, there is still some uncertainty in the details, namely where the heaviest precipitation will occur. However, with increasingly colder air working its way in, accumulating snow will be very possible with this storm. A ridge then looks to finally build in for the weekend bringing a break in the weather.

REST OF UTAH AND SOUTHWEST WYOMING

Strong south to southwesterly flow is expected across much of Utah and southwest Wyoming through the overnight period, with peak gusts approaching 45-50kts ahead of, and along, a cold frontal boundary. Light to moderate precipitation is also expected to accompany this cold frontal boundary, with conditions dropping into the MVFR category due to low CIGs. Snowfall in southwest Wyoming will likely drop conditions into IFR due to lower CIGs and VIS. Expect this frontal boundary to move through the region from east to west around 02-03Z through 10-11Z.

SLC WATCHES/WARNINGS/ADVISORIES

UT...High Wind Warning until 5 AM MST Tuesday for UTZ101-102.

Wind Advisory from 8 PM this evening to 5 AM MST Tuesday for UTZ103>105-121-128>130.

Winter Storm Warning until 5 AM MST Thursday for UTZ108-110>112.

Winter Weather Advisory until 5 AM MST Thursday for UTZ113-117.

Wind Advisory until 5 AM MST Tuesday for UTZ115-116-118-119-122- 126-127.

Winter Storm Warning until 5 PM MST Wednesday for UTZ125.

WY...None.