Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
500 FXUS65 KSLC 162145 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 345 PM MDT Mon Sep 16 2024 .SYNOPSIS...A fall storm system will cross the area tonight into Tuesday, bringing much cooler temperatures. Cool and unsettled weather will continue for much of the remainder of the week. && .SHORT TERM (Through 12Z Wednesday)...A broad low pressure system has moved into the Great Basin this afternoon. Ahead of it, southerly flow has increased quite noticeably over the area, resulting in some gusty winds. Winds have been strongest over western Utah where some gusts in excess of 50 mph have been observed. In the moisture and instability ahead of the system, have seem scattered showers and thunderstorms develop over northern Utah, where more favorable instability exists in the vicinity of the upper level jet. Some of these storms have produced gusty microburst winds and the threat will continue into the early evening. The cold front in association with the low is expected to move into western Utah this evening, spreading northeast through Tuesday morning, with the associated upper low following close behind. This will keep precipitation, rain with snow above 9000 feet, going through Tuesday morning before it lifts out Tuesday afternoon and evening. More notable, however, will be the drop in temperatures. Maxes Tuesday are expected to run 10-15F below climo tomorrow, feeling very much like fall. .LONG TERM (After 12Z Wednesday), Issued 418 AM MDT... A cool and wet pattern will remain in place for the latter half of the week as a weakening upper level low approaches the Great Basin, replacing the early week low that will be exiting to the northeast. Temperatures will be running ~10 degrees below normal areawide for this time of year. Stratiform rain will transition to more of a diurnally driven showery precip regime (with less coverage) as this low shifts east. There still remains some uncertainty regarding the pattern following the departure of the aforementioned low. ~37% of guidance brings another trough through the Great Basin that would reinforce the cool airmass and lead to more precipitation. However, the remaining ensemble members suggest that ridging will build back into the area that would result in drier and warmer conditions. By Wednesday morning an upper level low will be centered off the coast of northern California. Across the Great Basin, a cold front ahead of the trailing low pressure will move through the area with increasing cloud cover that will inhibit temperatures from warming much throughout the day. As the low slides down the west coast northern Utah will be positioned on the left exit region of ~100kt jet. This will help to increase ascent across northern Utah/SW Wyoming resulting in some showery precipitation. By Thursday this low starts to progress inland while filling in and weakening as it does so. Even still, PVA will help to enhance lift across most of the CWA on Thursday and Friday resulting in more widespread light stratiform precipitation. As the cold core moves over the Great Basin snow levels will generally be ~10kft with some light snow accumulations across the highest elevations. This low exits the area to the northeast by the weekend, however steep lapse rates and lingering moisture left in the wake of the low will help to spark some diurnal showers Saturday and potentially Sunday across northern Utah and SW Wyoming. These will likely be spotty showers that could contain some graupel and gusty winds. As mentioned, the pattern following this exiting low remains in question as a minority of ensemble members bring in another trough, whereas most begin a drying and warming trend thanks to a ridge building back into the area. && .AVIATION...KSLC...Gusty south winds will prevail over the KSLC terminal through around 02Z, with area showers continuing through much of the evening and overnight hours. Passing showers will have potential to produce wind gusts in excess of 25kts. Lowering cloud bases are anticipated through the night, with a round of persistent showers expected between 02-10Z. A brief break in activity will occur thereafter, before another round of showers develop mid- morning. .REST OF UTAH AND SOUTHWEST WYOMING...Gusty south winds are expected across the region through the remainder of the daylight hours. Widely scattered showers and an isolated thunderstorm are expected across the norther half of Utah and southwest Wyoming through the next 16 hours. During this period, cloud bases are expected to lower and begin to obscure the high peaks of the Wasatch. Most areas are expected to maintain south winds through the overnight period, however, gusts will drop off outside of passing showers. && .FIRE WEATHER...Winds have been gusty today ahead of an approaching fall trough, with gusts in excess of 50 mph reported over parts of western Utah. However, relative humidities have been high enough to avoid critical fire weather conditions. Showers and thunderstorms have developed over northern Utah, with a few strong to severe storms possible into the early evening. As the trough moves in tonight, precipitation will become more widespread over northern Utah, persisting through Tuesday as the trough moves through. The area will see much cooler temperatures in the trough`s wake, up to 20F below highs observed today. Gusty southerly winds will persist over southeast Utah, however, and relative humidities values are expected to drop enough there to result in marginally critical fire weather conditions. Unsettled conditions will continue through much of the week, with a second trough on Thursday bring a reinforcing shot of cooler air. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Wind Advisory until 9 PM MDT this evening for UTZ115-122. WY...None. && $$ SHORT TERM/FIRE WEATHER...Traphagan LONG TERM...Mahan AVIATION...Webber For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity