textproduct: Salt Lake City

KEY MESSAGES

- Dry and generally mild conditions will persist into early next week.

- Unsettled conditions return to the northern half of the area Tuesday night into the weekend, with periods of valley rain and mountain snow.

DISCUSSION

Early afternoon upper air analysis indicates broad upper level ridging across the Southwest, with a shortwave trough undercutting the ridge, across western Nevada. An active northern stream continues, largely impacting the Pacific Northwest into the northern tier of the Interior West.

The previously mentioned shortwave trough will shift east across Utah through Monday, bringing increased cloud cover through at least Monday morning. This will likely keep the normally colder valleys from radiating out as much as the previous nights. This may also allow inversions to moderate in the northern valleys to some degree. Even so, guidance suggests some patchy fog will be possible for the Cache and eastern Box Elder County areas...but timing of clouds will be key. For now only have a 20% chance of fog in these areas.

In the wake of this weakening shortwave trough, westerly to northwesterly flow will build into the region Monday afternoon into Tuesday as a shortwave trough embedded in the northern stream far to the north passes through Montana into North Dakota. Cold air advection in association with this flow will gradually decrease 700mb temperatures, likely weakening inversions across the northern valleys Tuesday. Flow will back briefly behind this shortwave trough later Tuesday into Wednesday.

As a landfalling atmospheric river and associated jet max impinge on northern Utah Wednesday, periods of valley rain and mountain snow will develop across northern Utah Wednesday morning, building south with time as the best dynamics shift into the region. 25th to 75th percentile snow water equivalent is around 0.30-0.80" for the northern mountains, except 0.40-0.90" for the Beaver River Range. With snow levels around 8500 feet initially, snow ratios will be atypical for the Wasatch, remaining under 8 to 9:1 or so.

Deep synoptic lift will shift to the east by early Thursday, with another lull in the action through Thursday afternoon into Thursday evening. A landfalling atmospheric river with associated jet max will again impinge on the area Friday into Saturday...but there is a wide variation in exactly how this unfurls through Saturday. Guidance has a broad range of solutions from the best jet dynamics remaining to the north to the jet shifting as far south as central Utah. Current forecast is sitting right around the 50th percentile, but given the "warm" nature of this AR, again snow ratios will be more reflective of the Sierras versus the Wasatch. 25th to 75th percentile snow water equivalent for this storm is around 0.50-1.50" across the northern mountains, less for most valleys (except Weber/Davis/eastern Box Elder County areas that tend to do well in westerly flow, atmospheric river scenarios). 25th to 75th percentile snow amounts for the mountains, however, are closer to 5 to 10 inches for the northern mountains, locally up to 15 inches in the Bear River Range, due to previously mentioned "warm" mid-levels. Ensemble systems are likely to come into better agreement in the next few cycles on the position of the jet and the resulting impacts on the Beehive State.

Something we can say with confidence...unless the guidance changes significantly, the threat of valley snow, particularly for the valley floors of northern utah is quite low for the next 7 days (less than 10% for the Wasatch Front, less than 20% for the Cache Valley and other colder, northern valleys that could have more stubborn cold pools).

REST OF UTAH AND SOUTHWEST WYOMING

Winds will remain light and terrain-driven, with VFR conditions prevailing and passing SCT- BKN high clouds. Although a brief period of LIFR CIGs developed this morning at KLGU, high clouds will limit this potential early Monday morning to only 20% between 14-17z.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...None.