textproduct: Salt Lake City

KEY MESSAGES

- Winds become south-southwesterly Sunday ahead of a series of incoming systems bringing elevated winds and gusts to the area through much of the week.

- Multiple chances for accumulating mountain snowfall exist this week, with the Tuesday night through Thursday system bringing significant snowfall to the majority of our mountains.

- The threat for valley snow continues to increase with the Tuesday night through Thursday system for nearly all valley locations with the exception of Lower Washington County and the lowest elevations in eastern Utah.

DISCUSSION

Southerly winds are beginning to increase early this morning as a strong trough just off of the west coast continues to nudge our way. Broad, southwesterly flow is in place in the mid levels, and will only increase in the near-term as a jet streak at the base of the trough strengthens. Winds at 700-mb will trend a bit more southerly just ahead of the first storm system, increasing to 50kts by Monday evening. At the surface, the HREF mean shows 35-40kt winds across western Millard, Beaver, and Iron counties Monday afternoon, just barely below advisory criteria. Winds are expected to remain elevated through Wednesday, though perhaps a bit lower than Monday.

The first trough will swing through the forecast area Monday night into early Tuesday morning, overspreading precipitation from southwest to northeast as decaying atmospheric river moisture surges northward. While the best moisture is well to our south, PW values may still approach 150-200% of normal. For context, some of the stronger AR events here may provide values near 300-400%...but we can be happy with up to 200%! Some areas (e.g. Salt Lake, Tooele valleys) may see some initial downsloping and drier low levels with the strong southwesterlies, but the mountains will likely see a period of heavy snowfall as this trough swings through, particularly across southwestern Utah. A surge of colder air will accompany this trough, too, with snow levels dropping to 4500-5000ft by Tuesday morning. Snow levels will continue to decrease, with most valleys (exception being St. George and lower elevations of eastern Utah) transitioning to snow by Tuesday night at the latest.

Southwesterly flow and associated orographically-forced mountain snowfall will persist, with upper-level diffluence ramping up precipitation rates just ahead of the next system by Wednesday morning. This second wave will bring another stronger cold front through the area Wednesday afternoon and evening, with a transition to westerly to northwesterly winds expected. Snow ratios will increase accordingly. Given such strong forcing and even some modest instability, we will also need to monitor the chances for snow squalls moving forward, particularly if they might impact the evening commute.

There are a few areas of uncertainty that ultimately influence current snowfall forecasts. In the mountains, higher spread can be attributed to subtle differences in flow direction, as well as finer-scale details in the wind profile and other mesoscale features. Across portions of the Wasatch Back in particular, snow totals will be highly correlated with how much precipitation is able to spill over into these lee valleys. Often, higher wind speeds result in more advection of precipitation into the lee, though the magnitude of this spillover will depend on again, finer scale details in the stability profile. Finally, there is of course, the lake-effect aspect which may enhance snow totals downwind of the Great Salt Lake. Currently, this chance is fairly low.

Enough rambling...how much snow can we expect? Keeping in mind the aforementioned uncertainties...in the mountains, broadly, expect around 1-2 feet, with locally higher amounts in favored areas near Brian Head and in the Wasatch. Across the Wasatch Back, current forecast snow totals are around 8-12 inches and higher near Park City. Across many valleys, 1-6 inches with higher amounts on benches and near Cedar City. All in all, while trends in forecasts may still change, these storm systems will bring colder, wetter systems statewide through at least Thursday.

REST OF UTAH AND SOUTHWEST WYOMING

SCT to BKN mid/high level VFR clouds will persist more or less through the TAF period. An approaching system will favor most non-sheltered terminals to see increasing south to southwesterly winds after sunrise Sunday, with many seeing gusts through the day roughly in the 20-30 kt range. Winds and gusts will decrease overnight but increase again quickly after sunrise Monday.

SLC WATCHES/WARNINGS/ADVISORIES

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