Sunrise 6:34 AM   Sunset 8:17 PM Moonrise 7:22 PM   Moonset 5:21 AM

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FXUS65 KSLC 230954 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 354 AM MDT Tue Apr 23 2024

SYNOPSIS
Above average temperatures remain in place through mid-week as high pressure dominates. A closed low system will progress inland through the second half of the week, bringing cooler and wetter weather into the weekend.

.SHORT TERM (Through 12Z/6AM Thursday)...A weak boundary continues to lift out of the region today, allowing for slowly warming temperatures across the northern third of the forecast area. A mid-level moisture axis will remain draped across the northern third of the area as well, bringing increased cloud cover and a few light mountain showers. It is unlikely that precipitation will reach the ground given how dry the near surface environment is, however, if anything does reach the surface it should be quite negligible (i.e. trace amounts). With a touch of mid-level instability and afternoon solar insolation, can't rule out an isolated, short-lived thunderstorm.

Pushing into Wednesday the pattern begins to change as a mid-level ridge axis begins shifting downstream of the area, opening the door to a closed low system. As this ridge axis shifts downstream, increasing moisture will be introduced to the region which will allow for increased chance of seeing measurable precipitation, mainly across the northern reaches of the forecast area. Further warming of the airmass is expected across the northern half of Utah and southwest Wyoming, however, a slight cooling trend will be noted across the southern half of Utah as the influence of the closed low begins to spread into the Southwest.

.LONG TERM (After 12Z/6AM Thursday)...The long term portion of the forecast period begins on Thursday with the closed low over SoCal opening up and ejecting across northern AZ/southern UT.
Deterministic models and associated ensemble members are now in fairly good agreement regarding this evolution. Some shower activity looks possible in the warm sector ahead of the trough axis, firing up along the spine of the central mountains through the western Uintas. Behind the associated cold front, additional showers are progged to spread in from the northwest through the day. While temperatures cool, the airmass will remain mild enough to maintain relatively high snow levels through the day, around 8.5-9kft.

Additional trailing features will quickly follow the initial trough, leading to the development of a mean longwave trough over the Western CONUS which will continue to bring unsettled weather into the weekend. Within this wave train, the next trough, a more subtle shortwave disturbance, is expected to cross the area Friday morning/afternoon, followed by a deeper trough Friday evening/ Saturday morning. Cluster analysis of ensemble members show mainly small differences in timing and amplitude of the trough pattern. As such, confidence is high in the overall pattern and evolution, with some uncertainty with the details. Friday looks to be the wettest day of this stretch of wet weather. PWAT anomalies in the 97th percentile of climatology are noted across portions of Utah on Friday, and ECMWF-based Extreme Forecast Index shows a signal for abnormally high QPF as well. Current forecast is carrying a 2.5-day total (Thurs morning through Saturday afternoon) of over 1.5 inches of QPF over the ridgelines, and around 1 inch or more in the adjacent valleys.

Colder temperatures will be associated with the Friday and Saturday systems. Widespread below normal afternoon max temperatures are expected both days, and snow levels are expected to fall to between 7-8kft. As such, expect mountain snow accumulations, potentially significant above 8kft. Still questionable at this time whether this will result in any signficiant impacts owing to sun angles and road temperatures.

There remains some uncertainty as to how quickly the storm systems exit the area. Deterministics have precipitation largely winding down by Saturday evening, although cluster analysis indicates a bit more spread. However, by Sunday afternoon, all clusters show the trough already east of Utah. Uncertainty increases again after that, but expect a general warming and drying trend through the early part of next week.



AVIATION
KSLC...VFR conditions will be maintained over the KSLC terminal through the valid TAF period. Mid-level cloud cover will remain in place through much of the day, only dissipating for a brief period mid-morning. Light and variable flow early this morning will return to a northerly flow around 16-17Z.

Rest of Utah and Southwest Wyoming
VFR conditions will remain in place through the valid TAF period across Utah and southwest Wyoming. Mid-level cloud cover, with elevated showers, will prevail across the northern half of the area. Winds across the northern third of the area will remain out of the north. For the southern two-thirds, expect predominantly southwesterly winds with afternoon gusts to around 25-30 mph.

SLC WATCHES/WARNINGS/ADVISORIES
UT...None.
WY...None.

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