Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
525 FXUS65 KSLC 161018 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 418 AM MDT Mon Sep 16 2024 .SYNOPSIS...Southerly flow will strengthen across the region today ahead of an approaching storm system. The cold front associated with this system will cross the region tonight, ushering much cooler air into the area for Tuesday. The main storm system will move through the region Tuesday, with cool and unsettled weather lingering through the remainder of the week. && .SHORT TERM (Through 12Z Wednesday)...An upper low spinning over northern California this morning is inducing a deep layer southerly flow downstream across the forecast area. A shortwave currently rounding the base of the upper low will lift across eastern NV through the day today as it pivots around the upstream low. Pressure falls ahead of this feature will strengthen the wind field across the forecast area, particularly across west central and southwest Utah where gusts will exceed 45 mph at times. Winds across areas further east, including the Sevier Valley and Panguitch/Bryce Canyon areas will also see enhanced southerly winds, however max HREF gusts indicate these should remain a little below the advisory threshold of 45 mph, and thus have held off on any wind headlines for these areas. The shortwave lifting through eastern Nevada will also increase large scale ascent across the forecast area this afternoon and evening. Moisture/instability will be most abundant across northern and eastern Utah, where showers and thunderstorms will develop by early afternoon. Deep layer shear will support organized convection, and a few storms may approach severe limits with gusty winds the main threat. Locally heavy rain will also be possible although any threat for flash flooding will require training as storm motions will be in excess of 40 mph. As the approaching upper low spreads across NV this evening through tonight, the associated cold front will lift northeast across the forecast area, ushering much cooler air into the region. Temperatures will trend 15-20 degrees cooler across northern Utah Tuesday, keeping temperatures confined to the 60s across northern valleys. The cooldown will be a bit more muted across southern Utah, where temps will trend 6-10 degrees cooler. As the upper trough axis lifts through the forecast area, fairly widespread precipitation will develop across northern Utah Tuesday morning through mid afternoon. Snow levels near 9000 feet will likely result in some minor accumulations across the upper elevations of the Wasatch/Uintas during the day Tuesday. .LONG TERM (After 12Z Wednesday)...A cool and wet pattern will remain in place for the ladder 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...VFR conditions will persist for the KSLC terminal through the period. Southerly winds will increased as the day progresses with gusts ~25kts during the afternoon ahead of an approaching low. Showers and isolated convection develop later in the afternoon with the potential for gusty erratic outflow winds. .REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist for the airspace through the period. Southerly winds will be increasing ahead of an approaching low. This will create gusty southerly winds during the day along with showery convective activity increasing across the north during the afternoon. These showers could produce gusty outflow winds along with frequent lightning. && .FIRE WEATHER...Southerly flow will strengthen across the region today ahead of an approaching storm system. These winds will gust in excess of 30 mph this afternoon across much of central and southern Utah, and in excess of 45 mph across zones 492 and 495. These winds coupled with afternoon RH in the upper teens to low 20% range will result in near critical fire weather conditions this afternoon and early evening over much of central and southern Utah. As the approaching storm system moves into the Great Basin today, showers and thunderstorms will increase in coverage across northern as well as eastern Utah. Some of these thunderstorms may become strong, and be capable of locally heavy rain in addition to strong outflow winds and lightning. The cold front associated with this storm system will push through the region tonight, ushering much cooler air into the region Tuesday. Temperatures across northern Utah will trend 15 to 20 degrees cooler Tuesday, while temperatures across central and southern Utah trend 6-10 degrees cooler. The passing storm system will bring fairly widespread precipitation to northern Utah Monday night into Tuesday, with some accumulating snow possible above 9000 feet. Drier air will remain in place across central and southern Utah, and combined with gusty winds will result in near critical fire weather conditions across zones 489, 494 and 498 Tuesday afternoon. This cooler air will remain in place through the remainder of the week with another storm system passing through the region during the latter half of the week. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Wind Advisory from noon today to 9 PM MDT this evening for UTZ115-122. WY...None. && $$ SHORT TERM... LONG TERM... AVIATION... FIRE WEATHER... For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity