Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
512 FXUS65 KSLC 242209 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 409 PM MDT Wed Apr 24 2024 .SYNOPSIS...An active pattern will begin Thursday and continue into the weekend, with valley rain and mountain snow. && .SHORT TERM (Through 12Z Friday)...Another mild, almost summer- like day across the region, though enjoy this afternoon as a big change is on the horizon. A more active pattern will begin Thursday and continue well into the long term forecast period. Afternoon upper air and satellite analysis indicates a slowly weakening upper level low near the southern California coast. Broad upper level diffluence is noted across portions of eastern Utah. Additional disturbances associated with the continued active northern jet are noted upstream. Thursday looks to be quite active, with the filling upper level low to the south and a shortwave trough crossing into northwest Utah later in the afternoon and evening. Looks at the CAMS, most of the members suggest a mean of around 500 J/kg of SBCAPE ahead of a weak cold front. This combined with deep layer shear around 15-20 kts and a relatively dry sub-cloud environment will be supportive of at least occasional dry microbursts and perhaps occasional small hail across mainly northern Utah and Uinta County, WY. The southern Utah convection associated with the filling upper level low is likely to be weaker and less likely to be electrified. The previously mentioned weak cold front will cross the region Thursday afternoon into late Thursday evening. Post-frontal showers will continue into Friday morning. Temperatures will be cooler Thursday afternoon, on the order of around 10 degrees or so. Light snow accumulations will be possible above 8500-9000ft, but any snow impacts will be focused on the long term forecast period. .LONG TERM (After 12Z Friday)...Active weather continues into the long term period as a stronger northern stream trough begins to dig into the region along with an attendant cold frontal boundary. Orientation of the jet will place the area in a favorable zone of diffluence/divergence, resulting in widespread precipitation, especially in combination with enhanced convergence and lift along the cold frontal boundary. Additionally, guidance shows at least some potential for some minor destabilization, thus could see some convective enhancement to precipitation through the day Friday, especially along the cold front. Deep layer flow will gradually shift from westerly to southwesterly through the day, with the trough axis eventually moving overhead and cutting off to an extent Friday night into early Saturday. As the trough then begins to shift further east, will see unsettled northwest flow and continued cold air advection maintained into Saturday, yielding another day of elevated precipitation chances across the region. Still a bit of uncertainty on how quickly the trough shifts out, but general consensus is deeper scale ascent will wane overnight into Sunday, but with enough marginally unsettled west- northwesterly flow continuing to result in isolated to scattered activity Sunday, particularly across the higher terrain and during peak daytime heating. Looking at some of the details, there is high confidence in much cooler weather settling in with this trough. Both Friday and Saturday will see afternoon highs drop to around 7 to 15 degrees below climatological normal, with temperatures starting to gradually rebound Sunday as the coldest H7 temperatures associated with the trough depart. Similarly, snow levels Friday will generally be around 7.5kft to 8.0kft or higher, dropping to as low as 6.5kft or so Saturday morning, and rising back to around 7.0kft to 7.5kft during the day Saturday with daytime heating. Exact amounts still carry some uncertainty, but general precipitation amounts of around 0.4" to 0.8" or so of water remain along much of the I-15 corridor, with liquid equivalent of around 0.8" to 1.6" for the high terrain across the region. As is typical, some locally higher amounts in favored locations will be possible. The ECMWF Extreme Forecast Index also continues to further highlight central Utah in particular for higher chances of seeing anomalously high precipitation in comparison to climatology for this time of year. With sufficiently low snow levels, this will result in some appreciable late season snow accumulations, with the best signal noted across portions of the Upper Cottonwoods, the High Uintas, the Manti Skyline, and the Tushar Range. At mid elevation areas more on the fringe of the snow level, the warmer antecedent conditions in addition to more favorable spring sun angle (during the day) will likely help abate more substantial accumulating snow at least to some extent. Moving into early next week, forecast specifics will largely depend on a deepening low dropping south from the Gulf of Alaska and it`s downstream effects on the longwave flow pattern over the CONUS. The general consensus carried amongst deterministic and ensemble guidance sources is that this deepening low will help amplify a broader ridge across much of the central CONUS, with the local region drying/warming in turn as a result of increasing southwesterly flow. Most uncertainty currently is noted in how quickly this ridge develops, and in turn just how strong it gets. For now, local forecast carries drier conditions and warming temperatures to well above climatological normal by midweek. && .AVIATION...KSLC...Northwest winds will prevail through around 04Z when winds transition to southeast. Light southeast winds will prevail overnight, but there is a low chance that outflow winds from showers to the northwest could switch winds to northwest for several hours any time from roughly 06-09Z. Scattered showers and thunderstorms are likely from 18Z into the evening. .REST OF UTAH AND SOUTHWEST WYOMING...Isolated showers in southwest Wyoming and northwest Utah will diminish into the evening. Outflow winds from showers in northwest Utah could enhance northwest flow through roughly 09Z throughout northern Utah. Gusty southwest winds will diminish into the evening throughout southern Utah. Scattered showers and thunderstorms are likely for southwest Wyoming and most of Utah from 18Z into the evening. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ Kruse/Warthen/Wilson For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity