Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
040 FXUS65 KSLC 222117 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 317 PM MDT Fri Aug 22 2025 .SYNOPSIS...With high pressure centered over the Four Corners, monsoon moisture will gradually spread northward into Utah and southwest Wyoming through early next week. This will bring increased coverage of showers and thunderstorms, the potential for flash flooding, and gradually less hot temperatures. && .SHORT TERM (Through 12Z/6AM Sunday)...As high pressure continues to nudge westward, moisture is increasing statewide within overall southerly flow, with PWATs reaching around 0.8-1.1" this afternoon. Scattered showers and thunderstorms have developed mainly over higher terrain, with only isolated outflow winds up to 45 mph observed; instead, we have transitioned more towards a flash flood regime, perhaps moreso than high-res guidance initially suggested. Moisture will further increase across the area heading into tomorrow, with a secondary moisture push arriving late Saturday into Sunday. Thus, tomorrow looks to be similar to today, albeit with a slightly higher flash flood threat and lower dry microburst threat. While model soundings still show a shallower dry layer at the surface both today and tomorrow afternoons, slow storm motions, modest instability, and above-normal PWATs will combine for this increased threat of localized flash flooding, particularly for prone areas like slot canyons or areas near recent burn scars. .LONG TERM (After 12Z/6AM Sunday), Issued 522 AM MDT... Monsoonal moisture is expected to become especially pronounced across the entirety of Utah and southwest Wyoming on Sunday into early next week, with PWAT anomalies pushing 150-200% of normal areawide. As such, expect widespread coverage of showers and thunderstorms each day, with this amount of moisture in the column favorable for locally heavy rainfall under stronger cores. The Weather Prediction Center continues to carry a Marginal risk (level 1 of 4) for excessive rainfall across the entire forecast area through at least Tuesday. Those with outdoor plans should continue to monitor the forecast given the associated risk for flash flooding. Locations with greatest threats for flash flooding include slot canyons, normally dry washes, slickrock areas, recent burn scars, and urban areas. While moisture availability will be plentiful, the one factor that could impact afternoon convective development and evolution includes the potential for nocturnal convection. If any nocturnal convection occurs and skies remain sufficiently cloudy, we could see more stable atmospheric conditions develop. This would inhibit the development of convection into the afternoon, instead favoring a more stratiform precip regime. Will be something to monitor as we get closer. In addition to widespread precipitation, this pattern will bring a much-needed gradual cooling trend throughout the long term period. Temperatures begin near-average on Sunday, dropping to around 5-10F below seasonal averages by the end of the week. && .AVIATION...KSLC...Moisture to continue to increase, corresponding to increase in shower/thunderstorm chances, primarily from early afternoon to evening. Convection will be capable of brief periods of moderate to heavy rain, lightning, gusty erratic outflow winds, and briefly reduced VIS/CIGS. Aside from precipitation, winds anticipated to follow a typical diurnal pattern (shifting SSE ~03- 05Z Sat, back NW 17-19Z thereafter). .REST OF UTAH AND SOUTHWEST WYOMING...A monsoonal moisture surge will result in a more active period, especially at southern Utah terminals. Shower/thunderstorm chances will be maximized early afternoon through the evening, and bring a threat of moderate to heavy rain, lightning, gusty erratic outflow winds, and briefly reduced VIS/CIGS. Outside precipitation, winds are expected to follow a largely typical diurnal pattern with magnitudes remaining modest. && .FIRE WEATHER...Moisture will continue to move into Utah from the south, with another secondary surge arriving Sunday. Coverage of showers and thunderstorms will continue to increase. Storms will become wetter, with increasing chances for wetting rain and decreasing chances for gusty outflow winds through at least Wednesday. Relative humidity will also improve accordingly. One area of forecast uncertainty is the amount of cloud cover, which may limit the intensity of any developing storms and therefore rainfall amounts, particularly after Sunday. Model guidance currently suggests moisture will peak around Wednesday, with a gradual decrease in moisture thereafter. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Extreme Heat Warning until 9 PM MDT this evening for UTZ123-124. WY...None. && $$ Cunningham/Whitlam/Warthen For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity