textproduct: Salt Lake City

SYNOPSIS

Dense fog has developed across several northern Utah valleys and Uinta County, WY. This fog will dissipate by late morning. Several disturbances will impact Utah Sunday through Thursday, though there is little threat of heavy precipitation.

DISCUSSION

While the pattern remains largely active across the West, Utah is likely to remain on the periphery of multiple storms through at least Thanksgiving. Early morning upper air and satellite analysis indicates an upper level low is shifting south along the California coast. The northern stream remains active through the eastern Pacific and into southern Canada.

As was the case Thursday morning, dense fog has developed across the Cache Valley and eastern Box Elder County. Dense fog has also developed across Uinta County, WY. Dense fog advisories are in effect for these locations, with visibilities less than 1/4 mile impacting the I-15 corridor from Brigham City to the Utah/Idaho stateline, routes in the Cache Valley and I-80 from near Echo Reservoir to Lyman, WY. Dense fog is developing along the Western Davis Corridor as well. Will keep an eye on dense fog development near the Great Salt Lake in Weber, Davis, and Salt Lake County and will expand dense fog advisories if needed. Regardless, commuters across these areas should be prepared for rapid decrease in visibilities through about 10 AM.

The previously mentioned upper level low will eject east and then north across the 4-Corners area. Ensemble consensus is the precipitation shield from this low will bring light precipitation to portions of south central and southeastern Utah Sunday, with the mean range from around 0.05-0.10", heaviest across eastern Kane County.

In the wake of this upper level low, a northern stream shortwave trough will dig into the northern Intermountain Region Monday into Tuesday. The majority of ensemble members now favor this trough to continue to dig into the central Rockies, bringing light precipitation to the northern mountains Monday afternoon into Tuesday morning. And by light, the cluster ensemble mean is 0.03" for the Bear River Range. The dusting of snow aside, this will usher in a colder airmass behind the cold front. Expect temperatures to fall around 5 to 10 degrees between Monday's highs and Tuesday's highs, especially across northern and central Utah. By Tuesday, the Wasatch Front will be struggling to reach the low 40s.

For lower Washington County and the Virgin River area between Springdale and St. George, this shift toward a colder solution has brought the threat of freezing temperatures both Tuesday and Wednesday mornings, especially outside of the St. George City area. the highest chance for a freeze will be Wednesday morning (around 30-40% chance, except in the St. George area where it is closer to a 10% chance due to northerly gap winds in the wake of the cold front). This would be the first freeze of the fall for these locations, so those with frost/freeze sensitive plants should continue to monitor the forecast and potential Freeze Watches and/or Warnings.

As just mentioned, there is the moderate potential for gusty gap winds Monday night into Tuesday morning and again Tuesday night into Wednesday morning behind the cold front across lower Washington County. These northerly winds would mainly impact areas near Black Ridge Canyon including Toquerville, Hurricane, and La Verkin. Right now, expectation is gusts will peak around 40-45 mph.

Looking ahead to Thanksgiving, a portion of the ensemble members continue to suggest northwest flow coincident with jet max will set up across northern Utah, bringing a period of precipitation. Around 50% of members would bring around 0.05-0.10" of precipitation to the northern mountains, lighter in the valleys, with some potential for at least a period of light snow for benches from SLC north. 25% of the ensemble members are significantly more pessimistic, with precipitation remaining well north of the Utah. And then there's the final 25% or so that suggest a deeper, colder system with up to 0.25" for the mountains, up to 0.10" for the valleys, with potential at least bench snow all the way to central Utah. This is something to continue to monitor if you have Thanksgiving travel, but given the models are in three main clusters, a weak system that brings very light precipitation, a dry period with precipitation remaining well north of the area and a much deeper, colder system...confidence in any particular outcome is low.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions exist across most of the airspace with some intermittent IFR/LIFR across northern valleys due to FG. This will burn off by mid morning. Otherwise, a few high clouds and dry conditions will continue along with light and diurnally driven winds.

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SLC WATCHES/WARNINGS/ADVISORIES

UT...Dense Fog Advisory until 10 AM MST this morning for UTZ103-107.

WY...Dense Fog Advisory until 10 AM MST this morning for WYZ021.