textproduct: Salt Lake City

KEY MESSAGES

-Winter weather advisories are now in effect for the northern and southern mountain areas starting tonight and continuing into Thursday.

-The period of heaviest snow (with rates at or above 1 inch an hour at times) across the northern mountains will occur between 3 AM and 4 PM Wednesday.

-Additional precipitation will occur across central and southern Utah later Thursday into Friday. 50% of the ensemble members suggest a period of moderate precipitation will occur later Thursday into Friday across southern Utah.

-After a break over the weekend, another storm cycle will begin Monday and continue for much of the next week.

DISCUSSION

With only the fourth winter weather advisory issued since January 1 now in effect, the active pattern that has been advertised for awhile is beginning. Early morning upper air and satellite analysis indicates a series of upper level lows from the Gulf of Alaska, south to off the central California coast, further south to near the Baja California peninsula. An atmospheric river is approaching the California coast this morning...and this combined with the previously mentioned upper level lows will have a significant impact on the forecast over the next few days.

Previously, significant spread across the ensemble suite reduced confidence in how widespread any precipitation would be in association with the combination of an ejecting upper level low, broad upper level diffluence associated with a jet max, and any interaction with the southern Sierra landfalling atmospheric river. With the 00Z ensemble suite, confidence is increasing as the majority of members cluster around a dominant solution.

A warm front is currently lifting north across central Utah. This front will continue to shift northward ahead of the an upper level low moving eastward toward the central California Coast this morning. Meanwhile, a strong upper level jet and associated atmospheric river will continue to shift into the Southwest. The best chance of precipitation along this lifting front through the evening will be across the higher terrain of northern Utah, where the confluence of orographics and warm front dynamics will support light precipitation.

Attention then turns to previously mentioned jet max, as upper level diffluence in deep, moist southwest flow builds into the region Tuesday night. IVT anomalies on the order of 97th percentile or so will couple with preferential orographics across the southern mountains to begin a period of moderate to heavy snow, especially for the typical areas near Brian Head and the Tushar Range. Snow levels will begin around 7500-8000 feet across the southern mountains and gradually lower 7000 feet or so through the day Thursday. Expect a general 6 to 12 inches with this round for the Brian Head and Tushar Range areas, with 2 to 5 inches above 8000 feet for most of the remainder of the southern mountains (25th to 75th percentile).

Similarly for the northern mountains, from roughly the Wasatch Plateau/Book Cliffs north, deep, moist southwest flow coupled with jet dynamics will bring a period of moderate to heavy mountain snow, starting near to after midnight tonight and continuing through Wednesday, shifting more showery Wednesday evening...and eventually diminishing Thursday morning. Expect 6 to 12 inches for the Wasatch and western Uinta ranges, with locally up to 15 inches for the upper Cottonwoods (25th to 75th percentile). For the Bookcliffs/Wasatch Plateau, expect 5 to 10 inches (25th to 75th percentile).

As the final upper level low ejects across the Southwest later Thursday into Friday, around 50% of ensemble members bring the precipitation shield on the north side of this circulation through southern Utah after 18Z Thursday. For now, the winter weather advisories for the southern Utah mountains end Thursday morning, but will need to monitor model trends for extension if the 50% of solutions that bring another round of moderate mountain snow become a more dominant solution.

After a break in the action next weekend, the active storm cycle continues through much of the next week. Looking through our 240 on the deterministic models shows little threat of the blocking ridge rebuilding across the West.

REST OF UTAH AND SOUTHWEST WYOMING

Increased low level cloud cover is expected across the northern portion of the airspace today as an influx of moisture from a decaying atmospheric river moves into the region. A band of precipitation moving northward this afternoon/evening across northern Utah and southwest Wyoming is expected to develop, with main impacts being lowered CIGS resulting in terrain obscuration. With snow levels around 6500 feet, this band has a 30% chance to bring a period of IFR/MVFR conditions to KEVW this afternoon and evening.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory from 11 PM this evening to 11 AM MST Thursday for UTZ110>113.

Winter Weather Advisory from 11 PM this evening to 5 AM MST Thursday for UTZ125.

WY...None.