Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
509 FXUS65 KSLC 302145 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 345 PM MDT Mon Jun 30 2025 .SYNOPSIS...Hot temperatures will continue through Tuesday. As mid-level moisture increases Tuesday into Wednesday, slightly cooler temperatures and increasing coverage of thunderstorms is expected. Thunderstorms will begin to wind down on Friday. && .DISCUSSION...Key points: * Above-normal high and low temperatures will result in a Moderate/Major HeatRisk on Tuesday for Eastern Box Elder County and the Northern Wasatch Front. * Increasing monsoonal moisture will result in increasing coverage of thunderstorms through Thursday, with storms gradually trending less dry. A dry microburst threat initially will transition into more of a localized flash flood threat by Wednesday and/or Thursday. * Increasing shear by Thursday/Friday may result in more organized thunderstorms. Satellite imagery this afternoon reveals a closed low spinning just off the coast of California, with developing convection across portions of Utah as mid-level moisture streams in from the south. As this low continues to slowly shift eastward, this will allow additional moisture to filter into the area. Precipitable water increasing to around 0.70-0.90" by Tuesday will result in increased instability for more widespread convection, first starting across the central spine of Utah`s mountains then also developing along the UT-NV border. Inverted-V soundings with steep lapse rates suggest the threat of gusty microburst winds, with the HREF max approaching 40-50 mph in many areas. SPC even has far northwestern Utah in a Marginal (Level 1 out of 5) risk for severe wind. Tuesday afternoon will be the hottest day of this stretch, with portions of the Wasatch Front approaching 100F and St. George reaching the upper-100s. Overnight lows will be fairly warm, only reaching down to around 70F along the Wasatch Front. HeatRisk has a wide swath of Major (Red) HeatRisk across portions of Eastern Box Elder County and the Northern Wasatch Front, thus Heat Advisories have been issued for these areas. By Wednesday, moisture advection will continue, with PWs reaching to near 1" (around 90-97.5th percentile), especially across southern Utah. The stubbornly slow upper level low will now be near the southern Sierras. With more forcing for convection, expect convection to increase in coverage on Wednesday. Storm motions will be on the slower side and may support a transition to a flash flood threat by Wednesday afternoon. Don`t expect widespread flash flooding, however, but those with plans in slot canyons, normally dry washes, slickrock areas, etc should continue to monitor the forecast as isolated flash flooding especially for those areas is increasing in likelihood. By Thursday, the previously mentioned Gulf of Alaska trough will combine with the upper level low and finally push this system out of the region. Another day of relatively widespread convection is expected...with the threat of isolated flash flooding continuing across the south. Deep layer shear may be sufficient across the north for more organized convection. && .AVIATION...KSLC...Predominantly VFR conditions are expected to persist today and tonight with typical evening wind shift around 1- 4Z. Cumulus development to the southeast over the Oquirrhs and adjacent ranges will send mid-level clouds over the terminal this afternoon/evening, but otherwise no impacts. Higher thunderstorm chances are expected tomorrow, bringing a threat of gusty and erratic winds in the afternoon and evening. The chance of a thunderstorm directly impacting the terminal or vicinity is currently less than 30%. Meanwhile, there is uncertainty in tomorrow`s wind shift; current thinking is south winds will prevail until erratic outflow winds arrive in the afternoon. .REST OF UTAH AND SOUTHWEST WYOMING...Increasing moisture will support greater coverage of thunderstorms tomorrow, particularly over the higher terrain east of I-15, though these are unlikely to impact flight categories. Rather, isolated gusty outflow winds of up to 40-50 mph remain the primary threat. Additionally, isolated locations in southern Utah (e.g. BCE) will again be impacted by wildfire smoke. For those areas, early morning stability will again allow for smoke to drive localized IFR conditions through ~15z. && .FIRE WEATHER...While thunderstorms this afternoon have been more isolated and limited to higher terrain, increasing moisture each day will result in higher coverage of thunderstorms through at least Thursday. Overnight RH recoveries will improve greatly, especially after tonight. Even tonight, many areas will see improvement, with the exception being across western valleys and in lower Washington county, where max RH will still be fairly poor, around 25-30 percent. Min RH will be a bit slower to improve through the week. Given this will be the first lightning after an extended dry period, there is a heightened threat of dry lightning and fire weather conditions on Tuesday afternoon. Any thunderstorms that develop Tuesday afternoon will be capable of producing gusty and erratic outflow winds up to 40-50 mph. This dry lightning threat could linger into Wednesday afternoon, though this may feature more of a mix of wet and dry thunderstorms. Friday is expected to be much drier than prior days, though afternoon thunderstorms are still possible. Additionally, another disturbance approaching Friday may bring a round of gusty southwesterly winds along with lower humidities. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Heat Advisory from noon Tuesday to midnight MDT Tuesday night for UTZ103-104. Red Flag Warning from noon to 9 PM MDT Tuesday for UTZ488-493- 496. WY...None. && $$ Cunningham/Kruse/Van Cleave For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity