textproduct: Salt Lake City

KEY MESSAGES

- An atmospheric river will bring ample valley rain and high- elevation dense mountain snow to northern Utah this evening through Wednesday morning. The warm nature of this storm will keep any snowfall confined to locations 8500ft and above.

- Windy conditions will exist tomorrow across ridgetops and other high elevation locations.

- Ridging builds back in Friday, lasting through the next 7-10 days bringing anomalously warm and spring-like conditions to the forecast area.

DISCUSSION

Currently, satellite water vapor imagery shows a broad band of moisture streaming over much of UT with mesoanalysis honing in on the more robust moisture streaming in over northern UT. This comes as no surprise for most across northern UT as steady rainfall has been ongoing for quite some time now with intensity increasing up to this point. IVT values roughly around 250-300kg/m*s will continue streaming across much of northern UT into the morning before the atmospheric river begins to decay at a faster rate, corresponding with a decrease in precipitation coverage throughout the afternoon hours.

An enhanced belt of WNW 700mb flow ranging from 35-45kts will gradually overspread the region this evening into tomorrow afternoon resulting in potentially strong gusts across ridgelines and across Uinta county, WY, where gusts ranging from 30-45mph are expected through the afternoon tomorrow. Most UT valleys could get breezy in the afternoon as a weak frontal feature passes through, though winds will struggle to mix down into valleys given robust boundary layer moisture in place across much of northern UT.

With temperatures remaining quite warm through the duration of this event keeping snow levels around 8000-8500ft, valley locations can expect rainfall to persist with no change in precipitation type. There appears to be a hard cutoff regarding who sees accumulating rainfall with locations north of Nephi seeing meaningful accumulations, and those south generally seeing about a tenth or less of rainfall. Most locations along the Wasatch Front / I-15 corridor can expect around 0.25-0.50" of rainfall through tomorrow afternoon, though there appears to be a corridor across most of Davis county and perhaps Weber county that may see more. The lower bounds of this forecast (25th percentile) are higher than surrounding locations, sitting around 0.30-0.40" of rainfall with an upper bound (75th percentile) around 0.40-0.60" of rainfall. These areas tend to do better within a moist southwesterly flow regime given lack of terrain blockage, potentially favoring the 0.40-0.60" range of this forecast. The benches of Davis, Weber, and even Salt Lake counties all indicate that there is a 75% chance of reaching and exceeding 0.50-0.70" of water with this event, with roughly a 20- 30% chance of reaching or exceeding an inch of rainfall.

With how high the snow levels are with this event, most snowfall will be confined to the highest elevation locations across the forecast area. This storm may be warm, though the highest elevation locations we have such as the Bear River Range, Upper Cottonwood, and high Uintas have the potential to see ample snowfall accumulations from this event. There is, however, still some uncertainty that exists with snow levels and how much rain will mix in with the snowfall, even at our high elevation locations. For example, the HREF 25th-75th percentile snowfall forecast ranges from 4-24" at Alta, which is quite the spread given this system is knocking at our door. Despite this, ensemble guidance favors the former, with an ensemble mean around ~12-17" across the Upper Cottonwoods. As such, confidence continues to remain high regarding ample snowfall accumulations across our highest elevation locations, though the "bust" solution still exists where we mix in too much rain and don't see much in the way of meaningful snowfall accumulations with this storm.

Precipitation will come to an end late tomorrow afternoon as a ridge of high pressure begins to build in. Confidence remains quite high regarding this ridge remaining in place over the forecast area through the next 7-10 days, resulting in a notable warm-up areawide potentially bringing temperatures to around 10-15 degrees above average by Friday for much of the forecast area. In fact, the St. George area will see temperatures up to 20 degrees above normal starting Thursday, potentially creeping as high as 80F in some areas by the end of the week. Around the middle of next week, a closed low will develop off the CA coastline, progressing inland and potentially impacting our area. Ensemble consensus unfortunately continues to trend further south with this setup, keeping geopotential heights higher across northern UT. As such, subsidence will remain higher yielding ample confidence that this period remains dry for the northern half of the forecast area with a chance at some precipitation across southern UT given it doesn't trend further south.

REST OF UTAH AND SOUTHWEST WYOMING

For northern terminals, a moist Pacific storm will impact the area into Wednesday, with the heaviest most persistent precipitation overnight into Wednesday morning. High snow levels will result in the majority of terminals seeing rain. Periods of MVFR conds will be possible during heavier rain, with IFR or lower anywhere precipitation does switch to snow. Winds will tend to favor S to SW directions, with variability from precipitation. A frontal boundary will move through Wednesday morning into the afternoon, with terminals largely seeing a WNW shift thereafter. For southern terminals, more benign weather expected with high clouds and winds generally less than 10 kts.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory until 5 PM MST Wednesday for UTZ110>112.

WY...None.