textproduct: Salt Lake City

KEY MESSAGES

- Wind gusts in excess of 45 mph will continue into Friday for at least portions of western Utah.

- A general 6 to 12 inches of snow can be expected Friday through late Saturday across the higher terrain of Utah, with locally up to 20 inches for the upper Cottonwoods and Bear River Range.

- There is a 60 to 80 percent chance of measurable snow for the valley floors of northern Utah Saturday night into Sunday morning.

DISCUSSION

Utah remains under a relatively strong southwesterly flow aloft ahead of a low pressure system churning off the Oregon and NorCal coast. Meanwhile, the moisture plume from the recent atmospheric river has moved off to the east, leaving Utah with just some showers (and isolated thunderstorms) mainly over and near the northern Utah mountains which should trend downward this evening. Given H7 winds of 40-45kt and a favorable south-southeasterly surface gradient, winds have remained strong through the day, with gusts in excess of 40 mph fairly common across the western Utah valleys. These winds have also aided mixing, providing for another day of temperatures well above normal for this time of year.

Expect the gusty winds to continue into tomorrow, though they should be a bit weaker based on surface-H7 trends. Some areas across western Utah are expected to continue seeing Wind Advisory criteria, including the north end of the Oquirrhs and Stansburys tonight and mainly the west-central valleys tomorrow afternoon. Have downgraded the High Wind Warning for the Tooele Valley to an Advisory given the trends in observed and forecast winds. Current areal coverage of the Wind Advisory may be too large for tomorrow, but will let ride for now.

Models show the upstream low gradually filling and tracking southeast tomorrow as an embedded shortwave trough ejects out of it and lifts across Idaho into western Montana tomorrow afternoon. The ejecting wave will send a baroclinic zone into far northern Utah tomorrow afternoon. Precipitation is expected to fill in over the northern Wasatch and Bear River Range tomorrow morning before spreading to the rest of the northern Utah mountains tomorrow afternoon. Meanwhile, another moisture plume will round the base of what's left of the low, with some enhanced moisture entering Utah from the southwest tomorrow afternoon. However, this moisture is not nearly as significant as the latest atmospheric river event. Although the airmass will cool a bit tomorrow, H7 temperatures between -2 and -5C will maintain snow levels on the high side, between 6500-8000ft.

Another trough carving in from the northwest for tomorrow night through Saturday will bring colder air to the area. Initially, this will help advance the existing baroclinic zone farther south, and combined with the increasing moisture from the southwest, expect precipitation to fill in across the area. Heaviest precipitation rates are expected tomorrow night through Saturday morning. Snow levels will gradually lower throughout this time, although perhaps not quite reaching the valleys floors. If snow does fall on the valley floors, given antecedent and soil temperatures, very little to no accumulation is expected through Saturday morning.

A secondary baroclinic zone associated with the deepening trough is then expected to move into Utah from the north Saturday afternoon. This will bring a much cooler airmass to the area. Precipitation along this boundary will have the potential to bring snow to the valley floors late Saturday into early Sunday morning. Currently, the NBM has a 60-80% chance of measurable snow along the Wasatch Front. Amounts should not be very significant given a relatively short accumulation window as the colder air will also be much drier. This drier air will also have a negative effect on lake- effect potential. While some lake-effect snow showers or lake enhancement cannot be ruled out, latest local guidance only has up to a 24% chance of occurrence, mainly affecting the western SL Valley and Oquirrhs late Saturday night into early Sunday morning. Precipitation should be largely done areawide by late Sunday morning. In the wake of the cold front, however, gusty canyon winds in Washington County will be a possibility. Currently, the NBM is not terribly excited, with less than a 30% chance of gusts 45 mph or greater, but cold advection with H7 flow of 35-40kt and a good northerly surface pressure gradient supports enhanced winds for sure.

For the early through middle part of next week, high pressure is expected to dominate the pattern. This will result in drier conditions with lighter winds, along with cooler surface temperatures as valley inversions strengthen.

REST OF UTAH AND SOUTHWEST WYOMING

Enhanced southerly winds gusting in the 25-35 KT range will persist across the area through tonight and into the day Friday. Blowing dust will reduce visibility to around 5SM across portions of northern and west central Utah through this evening, while showers and isolated thunderstorms persist across far northern Utah. Friday afternoon a cold front will cross northern Utah switching winds to northwesterly. Showers and a few thunderstorms will follow this front across northern Utah/southwest Wyoming later Friday afternoon and Friday evening.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Wind Advisory until 5 PM MST Friday for UTZ101-115-122.

Wind Advisory until 10 AM MST Friday for UTZ102.

Winter Weather Advisory from 11 AM Friday to 5 AM MST Sunday for UTZ110>113.

Winter Weather Advisory from 5 PM Friday to 5 PM MST Saturday for UTZ117-125.

WY...None.