textproduct: Salt Lake City

KEY MESSAGES

- Dry, relatively warm conditions will continue through Tuesday.

- An unsettled pattern will develop mid to late in the week, bringing an increasing threat of valley rain and mountain snow to northern Utah. Southern Utah will remain dry.

DISCUSSION

Early afternoon upper air and sounding analysis indicates broad upper level ridging persists across much of the Southwest with an active northern jet stream across the northern tier. Temperatures are again well above normal, though a few degrees cooler than Friday.

The mean ridge will shift east with time through the weekend as a weakening shortwave trough undercuts the ridge into the Great Basin Monday. Best case this brings increased clouds to the region.

As the next strong jet max impinges on coastal areas of the Pacific Northwest Monday into Tuesday, zonal to northwesterly flow will build across northern Utah by Tuesday afternoon. While light precipitation is possible across the far north as early as Tuesday afternoon into Tuesday evening, any heavier precipitation will await preferential jet dynamics Tuesday night. A combination of preferential jet dynamics and deep lift will support moderate to heavy precipitation across northern Utah Wednesday. Around 90% of ensemble members have clustered around a mean of 0.25" by Thursday morning for Alta, whereas in the Bear River Range the mean is closer to 0.35 or so. Given 700mb temperatures around -7C or so, this should give the northern mountains around 1 to 4 inches of snow, locally up to 6 inches, particularly for the Bear River Range. Some light snow is possible even for valley floors at times, most likely in heavier precipitation. No accumulation is expected at this time, however.

A break in the precipitation is expected Thursday morning, with another period of preferential jet dynamics building into the northern half of the state later Thursday into Friday. Like a previous landfalling atmospheric river event, the impact on Utah will depend on the exact location of the jet. Around 40% of ensemble members keep the jet further north and and east and thus reduce the overall precipitation totals for northern Utah, especially south of I-84. For now, the forecast is close to the NBM mean, with around 1.00-1.75" of snow water equivalent across the northern mountains between Thursday and Saturday. Note though, like most northwest to west flow atmospheric river events, snow levels will rise, impacting snow ratios. This will reflect in potential snow totals, with a 6 to 12 inches of snow for the northern mountains in the current forecast. Will need to keep an eye on snow liquid ratios as guidance tends to bring these to values too high for atmospheric river events (one this year had SLRs closer to 6 or 8:1 rather than our typical Utah powder snow).

No headlines are planned at this time.

REST OF UTAH AND SOUTHWEST WYOMING

Winds will remain light and terrain-driven, with VFR conditions prevailing and passing SCT- BKN high clouds.

SLC WATCHES/WARNINGS/ADVISORIES

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