textproduct: Salt Lake City

KEY MESSAGES

- Another impulse of moisture will pass through northern Utah from Sunday through Tuesday, bringing another round of high elevation snow and valley rain, primarily for areas north of the I-80 corridor.

- Breezy southwest winds are expected each afternoon from Sunday through at least Thursday as Utah and southwest Wyoming remain southeast of a broad upper level trough positioned offshore of the Pacific Northwest.

- After a relative lull in active weather early next week, another Pacific storm will bring another round of valley rain and mountain snow Christmas Eve and Christmas Day.

LONG TERM (After 12Z/5AM Wednesday)

Ensemble guidance remains in great agreement with enhanced southwesterlies aloft overspreading the region ahead of trough which is expected to meander off the Pacific Coast. This will result in an atmospheric river transporting ample moisture to the region resulting in persistent and widespread precipitation across the forecast area Wednesday through at least Friday.

On Wednesday, winds look to increase in magnitude across the region as a deepening shortwave embedded within the mean flow traverses across northern UT throughout the day. Additionally, this shortwave is expected to overlap with the arrival of moisture within the atmospheric river which is expected to kick off our prolonged period of precipitation across the forecast area. Given the warm nature of atmospheric rivers, snow levels are forecast to remain high keeping snow contained to higher elevation locations. With this setup, valley locations across the forecast area can expect rain as the main precipitation type through the duration of the event. This general pattern is expected to persist through at least Thursday as the upper trough remains parked off the Pacific Coast.

Come Friday and Saturday, ensembles begin to diverge somewhat which will impact storm coverage, accumulations, and timing. Roughly ~40% of guidance erodes the upper ridge over the central U.S., enabling the trough to eject inland on Friday resulting in an earlier arrival time of higher precipitation rates. The other ~60% of guidance, however, maintains the ridge over the central U.S. and continues to stall the trough off the West Coast resulting in weaker precipitation rates, though much more prolonged. On Saturday, ensembles diverge further with around ~40% of all members maintaining higher geopotential heights to our north, resulting in the trough ejecting inland and perhaps developing a cutoff low to our south. The other ~60% keep a broad open wave as it pushes inland, though there are still some timing differences that are evident within the ensembles. While there remains considerable uncertainty past D6, confidence remains high in a relatively active and potentially significant period of weather for the forecast area developing as early as Wednesday, lasting into the weekend.

Lastly, this forecaster hates to be the bearer of bad news, but this pattern generally sets us up for a "wet" Christmas rather than a "white" Christmas. With temperatures Wednesday through Friday running roughly 15-20F above average across the majority of our valley locations, conditions will be dreary and wet for most of the population of our forecast area. Fortunately for us, however, a white Christmas is still attainable, granted you feel the urge to drive up to higher terrain.

AVIATION...KSLC

Northerly winds appear well established now through the majority of the period, though brief directional changes to southerly may be possible over the next couple hours. Isolated showers are possible near the terminal in the afternoon hours, though confidence remains low at this time regarding impacts to the terminal. Borderline MVFR CIGs with mountain obscurations will persist through 13z before clearing up somewhat and raising. Otherwise, VFR conditions persist with a southerly wind shift around 02z.

REST OF UTAH AND SOUTHWEST WYOMING... Isolated showers are possible this morning and early afternoon across our northern UT sites, clearing up by the late afternoon. Additionally, mountain obscurations will persist through 13-14z before clearing up somewhat. Regarding KEVW, gusts greater than 20kts will persist through the TAF period with occasional showers and MVFR CIGs through the next couple hours.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory until 5 PM MST this afternoon for UTZ112.

WY...None.