textproduct: Salt Lake City

KEY MESSAGES

- A warm Pacific system will rain and mountain snow to northern Utah Tuesday morning through Wednesday afternoon, with the best accumulations above 9,000 feet. - High pressure is expected to move back in Thursday, with dry and mild conditions persisting through at least the first half of the weekend.

DISCUSSION

Seeing a predominately westerly flow over Utah and southwest Wyoming this evening with shortwave energy moving over the top of the ridge that has been over us for the past few days. Satellite derived PW values have increased by about 0.10 inch since this morning, showing moisture is already starting to creep back into the area. The moisture surge for northern portions of the area is on track to ramp up significantly Tuesday morning as the flow taps into a decaying atmospheric river. This will bring PW values, currently near median values, to in excess of the 90th percentile for this time of year.

As is often the case with atmospheric river events, temperatures will remain very much on the mild side, keeping snow levels primarily in the 7,000 to 8,000 range, with the most significant accumulations occurring above about 9,000 feet. Going Winter Weather Advisories for the northern mountains above 8,000 feet cover this threat well. The heavy, dense nature of the snow falling on top of lighter snow will also increase the avalanche danger for the mountains of northern Utah, which has already been considerable. Some precipitation will start as early as tomorrow morning for locations near the Utah/Idaho border, spreading across much of the remain of northern Utah during the afternoon. The most likely time for heaviest precipitation will be Wednesday morning as another shortwave moving over the top of the ridge brings a cold front through the area. Still seeing a bit of uncertainty as to how far south the boundary will go, but guidance this evening has trended just a bit warmer on average for the forecast area.

The majority of precipitation will taper off by Wednesday evening as high pressure makes its way back over the area, bringing a return to dry conditions with temperatures staying rather mild. Confidence is still relatively high on dry conditions continuing for the first part of the weekend. A return to a more active pattern looks a bit more likely than not for Sunday and beyond due to the presence of another Pacific trough. However, there remains quite a bit of spread with regard to the evolution and potential timing with that low. Given that guidance often struggles with such closed low features, anticipate the variety in the solutions to continue for the near future.

REST OF UTAH AND SOUTHWEST WYOMING

Winds will remain largely diurnally-driven during the overnight hours, increasing out of the southwest after 18z particularly across NE-UT/SW-WY. Showers will begin to move into the area after 13z along the UT-ID border, becoming more widespread down to roughly KDTA-KPUC by 21z. Precipitation type will be rain at most sites, though KEVW could start out as snow around mid-day before likely transitioning to rain during the afternoon. Mountain obscuration is likely across northern UT, with the potential for MVFR CIGs during the afternoon and evening.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory from 8 AM Tuesday to 5 PM MST Wednesday for UTZ110>112.

WY...None.