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Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
602 FXUS65 KSLC 252220 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 420 PM MDT Tue Jun 25 2024 .SYNOPSIS...Showers and thunderstorms will spread across the state on Wednesday with a gusty wind threat across northern Utah and isolated flash flood risk across southern Utah. Another round of strong thunderstorms is expected Thursday afternoon and evening. After briefly cooler temperatures Friday, hot and dry weather returns across the state this weekend. && .SHORT TERM (Through 12Z Thursday)...Moisture remains in place across southern Utah this afternoon, with a PW gradient from around 1 inch near the AZ border dropping off to less than 0.7 inches north of I-70. Combined with daytime heating, CAPE values around 500-1000 J/kg of CAPE, this environment is support diurnal convective development across southern Utah. Light westerly flow is favoring downstream convective development on a cold pool across the eastern Grand Staircase moving toward Lake Powell. This is where the highest Flash Flood potential will continue in the near term. Tonight, an shortwave moving northward through AZ around the western periphery of the SW high pressure, will track into southern Utah, and will interact with weak surface boundary and moisture gradient over southwestern Utah. This will increase the potential for showers and thunderstorms over St George, Zion, Cedar City and north to Beaver tonight. In particular, there is an increased potential for training and redevelop along the stalled boundary over southwest Utah overnight tonight, which is when the isolated flash flood potential will peak for the aforementioned areas. As this wave continues to work northward overnight and interacts with the increasingly dry airmass into central Utah, the convective hazard will transition from Flash Flooding to more of a gusty outflow wind potential. This will also increase southerly winds and cloud cover all the way into central and northern Utah by early Wednesday morning. This will help to limit cooling overnight tonight, allowing for one more warm night, with minimal overnight relief from the daytime heat. On Wednesday, the aforementioned shortwave will be ejecting northeastward into WY/CO leaving Utah under subsidence behind the wave. This will help to allow for breaks in the cloud cover and increase diurnal heating through Wednesday morning, with more widespread moisture in place across the state of Utah. By Wednesday afternoon, another weak wave in the west-southwesterly flow will increase ascent and aid in convective initiation. Showers and thunderstorms will become more widespread on Wednesday, especially south of I-80 and through central Utah. Across the northern half of the state, the primary hazard will be gusty outflow winds, with perhaps a few isolated severe wind gusts. Otherwise, for southern Utah, deeper moisture in place will act to limit the wind potential, instead favoring another day of an elevated Flash Flood potential, mainly for portions of the Grand Staircase, Glen Canyon, Capitol Reef and the San Rafael Swell. .LONG TERM (After 12Z Thursday), Issued 428 AM MDT... A progressive pattern will develop for the long term period as the ridge of high pressure responsible for the recent heat will shift east into the southern CONUS. Ample moisture will only be in place on Thursday as the first trough pushes through to our north. A dry airmass will be ushered in behind the aforementioned trough. This airmass will help to cool temperatures briefly, but the dry conditions will persist through the remainder of the period. This dry airmass will pair with windy conditions as another trough moves into the region this weekend resulting in favorable fire weather conditions. The approaching trough on Thursday will pair with PWATs (~1.2" for KSLC) approaching climatological maxes for this time of year. Forecasted CAPE values near 1000 J/kg and bulk shear >50kts will create an atmosphere conducive for strong to severe thunderstorms across the CWA. The limiting factor, however, will be how much precipitation and cloud cover will be lingering across the region from the previous days convective activity. A lot of the hi-res guidance does keep precipitation ongoing Wednesday night into the morning on Thursday. If these showers are able to dissipate early enough then the atmosphere could become primed for strong thunderstorm development as the axis of the trough passes through Utah and SW Wyoming. In addition to the threat of severe weather, flash flooding will also be a concern across flood prone regions such as dry washes, slot canyons and burn scars. This precipitation will quickly shift east and out of the CWA late on Thursday as drier and cooler air advects in behind the frontal passage. Friday`s high temperatures will be the coolest of the long term period with near normal temperatures. Shortwave ridging will temporarily build back into the area on Saturday leading to high temperatures returning to ~5 degrees above normal. Similar temperatures on Sunday along with increasing southwesterly flow ahead of our next trough will lead to gusty winds developing across most of the CWA. The dry airmass will be characterized by minimum relative humidity values <15% for the afternoon on Sunday. The trough axis will push east of us on Monday with temperatures the remainder of the period returning to near normal and winds weakening slightly, but staying elevated. && .AVIATION...KSLC...Northerly winds remain in place over the KSLC terminal through the daylight hours, reverting back to a southerly flow around 04Z. Mid-level cloud cover will increase through the overnight hours with CIGs remaining around 12kft AGL. Vicinity shower activity will increase through the morning hours tomorrow, and may bring gusty and erratic winds after 12-13Z. .REST OF UTAH AND SOUTHWEST WYOMING...Widely scattered showers and thunderstorms will continue through the remainder of the day across southern Utah, bringing areas of heavy rainfall as well as gusty and erratic outflow winds. Showers will continue into the overnight hours across the western half of Utah, spreading northward by the early morning hours. A similar threat of gusty and erratic outflow winds will exist through this period over western Utah. Otherwise, winds will continue to follow diurnally driven trends outside of local showers and thunderstorms while maintaining VFR conditions and CIGs around 10kft or above. && .FIRE WEATHER... Moisture remains in place across southern Utah this afternoon supporting continued isolated to widely scattered shower and thunderstorms this afternoon, with an isolated flash flood threat. This evening a wave will move northward out of Arizona and brining additional moisture northward across the state of Utah for Wednesday. Locally heavy rain is possible this evening over southwest Utah as this moves northward, transitioning to a gusty outflow wind potential across west-central Utah tonight as this continues moving northward. On Wednesday, the more widespread moisture will result in higher afternoon humidity values as well as a more widespread shower and thunderstorm potential. A few storms could be strong with isolated small hail, and gusty outflow winds, particularly across central Utah, and perhaps portions of northern Utah. Across southern Utah, the storms will be more capable of locally heavy rainfall and isolated flash flooding. Thursday, a trough moving in from the northwest will introduce a drying trend from west to east, which will favor showers and thunderstorms over eastern Utah with lowering humidity values across western Utah. By Friday into through the weekend, another Pacific trough will move in to our northwest which will continue to support a west- southwesterly flow of drier air moving into the area. The potential for critical fire weather conditions (low RH and winds) will start across southwest Utah on Friday, expand across more of western Utah on Saturday, more statewide by Sunday, then shift to the southeastern portion of the state by Monday as a weak cold front moves into northern Utah. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 11 PM MDT this evening for UTZ101- 104>106-116. Heat Advisory until 11 PM MDT this evening for UTZ102-103-107- 118-119. WY...None. && $$ SHORT TERM...Church LONG TERM...Mahan AVIATION...Webber FIRE WEATHER...Church For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity