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FXUS65 KSLC 272045 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 245 PM MDT Sat Apr 27 2024

SYNOPSIS
Cool conditions will continue into Sunday with a few lingering showers as an upper low exits the area. Temperatures will then gradually warm through Monday before a series of mostly dry cold fronts impact the region beginning midweek.

.SHORT TERM (Through 12Z/6AM Monday)...A broad upper low appears to be centered just east of the Four Corners region this afternoon, resulting in cool and unsettled conditions over Utah and southwest Wyoming. In this airmass, temperatures are averaging 10-15F below seasonal normals with widespread cloud cover.
Precipitation earlier was most widespread with an area of upper level divergence near and west of the Great Salt Lake, producing some significant water totals and some issues with standing water in that area. With the eastward movement of the low, associated precipitation has tended to diminish and the focus has shifted east a bit. Showers over central and southern Utah have become spotty at best, so have cancelled the Winter Weather Advisory for that area. With a bit better coverage of showers over northern portions of the forecast area, have allowed that advisory to continue for a bit longer.

Remaining showers are expected to all but diminish overnight as the low continues to pull away from the area. However, northern Utah is expected to see some redevelopment of showers during the day Sunday with the passage of a trailing weak shortwave. Warm advection in the airmass behind the low will allow temperatures to become less cool, averaging 5-7F below normal for this time of year. Any lingering showers are expected to diminish by Sunday evening.

.LONG TERM (After 12Z/6AM Monday)...While the long term forecast features a somewhat active and uncertain progression, there is a low chance of any impactful weather through the period.

For Monday and Tuesday, confidence remains high in an active storm track through the northern Rockies / Montana with generally zonal flow across Utah. On Monday a shortwave will graze northern Utah allowing temperatures to increase slightly ahead of the wave Monday, invigorate some showers across northern Utah (especially the mountains), followed by a slight cooling/drying trend into Tuesday behind the wave passage. Temperatures will be fairly unremarkable, for northern Utah, running a few degrees above average on Monday and a few degrees below average on Tuesday. Meanwhile southern/central Utah remains displaced enough from the shortwave passage to support continued dry and slightly above normal temperatures south of the boundary.

By Wednesday, a trailing wave is forecast to move through the Pacific Northwest and into the intermountain West. However, per cluster analysis about 50% of ensemble solutions maintain a shallower wave that ejects more eastward which allows for maintenance of zonal flow across Utah and continued drier, near seasonal conditions. Meanwhile the other 50% of solutions dig the wave further southward, swinging the wave through Utah. These solutions feature cooler temperatures across the Great Basin and through Utah as a cold front is force across the region. However, as far as sensible weather impacts go, that is about it, as these further south solutions are also moisture starved. At most, would expect a few scattered showers, mainly in the northern Utah terrain.

For Thursday through Saturday, the ensemble mean solution is a fair nondescript zonal flow across the western US and Great Basin.
Breaking this down via the cluster analysis reveals about 25% of solutions develop a deeper trough over the western US, just upstream from Utah. Another 25% develop some very weak ridging over the western US, while the remaining 50% of solutions in the middle have some sort of weak troughing to nearly zonal flow across the area.
Picking apart the clusters further, its really only the upper echelon (10%) of the deeper trough clusters that produce any significant precipitation across the area, which would manifest as valley rain and accumulating mountain snow. Otherwise, the vast majority of most solutions support roughly seasonal temperatures with some occasional passing showers.

AVIATION
KSLC...Shower activity expected to continue to gradually diminish as system departs, but periods of CIGS generally to MVFR will remain possible with any shower activity over the terminal.
Otherwise, will see some mountain obscuration from cloud cover, but trend will be towards partial clearing late evening into the overnight hours. Aside from influence of nearby showers, anticipate winds to largely follow a typical diurnal pattern. An isolated shower or two may redevelop Sunday, but activity much less widespread.

REST OF UTAH AND SOUTHWEST WYOMING
Active weather system will continue to depart the region, with shower activity gradually diminishing late evening into the overnight hours accordingly.
Reduced CIGS (generally to MVFR) possible during periods of showers, but otherwise should also see something of a partial clearing trend.
Winds will also start to relax some late evening into the overnight, with a bit more diurnally typical winds expected Sunday. Some redevelopment of isolated showers will remain possible (~20% chance)
on Sunday.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Winter Weather Advisory until 6 AM MDT Sunday for UTZ111-112.

WY...None.

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