Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
835 FXUS65 KSLC 110939 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 339 AM MDT Tue Jun 11 2024 .SYNOPSIS...Very hot temperatures will build into the region Wednesday into Thursday, with the potential for the Wasatch Front to breach the century mark. An upper level low may bring cooler temperatures and precipitation by Friday. && .SHORT TERM (THROUGH 00Z FRIDAY)...Current large-scale pattern depicts a broad but generally low-amplitude ridge building into the Great Basin while a cutoff low continues to meander along the Baja Coast. Utah remains mostly cloud-free this morning with the exception of far southeast Utah as a drier airmass continues to work into the area. A few high-based showers remain possible this afternoon from what is left of the moisture, with most CAMs indicating weak activity over portions of the southern mountains through the east-central valleys. Temperatures will be the main issue for the short-term forecast period. Underneath the building ridge, the airmass will trend warmer. Global deterministic models indicate a dome of H7 temperatures of 17-18C by Wednesday and around 16-17C for Thursday. Each of these two days will see temperatures well above climatological normals for this time of year. Even though H7 temperatures are slightly cooler on Thursday compared to Wednesday, increasing southerly flow will aid in mixing. On the other hand, there is also the potential for increased sky cover on Thursday. Nevertheless, HeatRisk (though slightly less excited compared to previous forecasts) continue to show enough of a threat of excessive heat to warrant an upgrade from an Excessive Heat Watch to a Warning for the Glen Canyon zone. Have contemplated heat highlights for other zones as well. However, the St. George zone ended up being more marginal. Some northern valleys may eventually need highlights as well, but this looks more like Advisory level with the best chance on Thursday, so have opted to punt to future shifts. It should be noted, however, that the latest NBM has a 38% chance of SLC reaching 100F on Wednesday and a 48% chance on Thursday. .LONG TERM (After 00Z Friday/6PM Thursday)...Friday marks the transition to more unsettled weather across northern UT and southwest WY, at least to start the long-term period. A closed low over SoCal will weaken as it moves inland, tracking across southeastern UT on Friday and bringing a decent mid-level moisture surge with it...PWATs across southeastern UT jump from an ensemble mean of 0.35" up to 0.75". Thus, scattered showers will develop in eastern UT beginning late Thursday night, with thunderstorms and high-based convection developing Friday afternoon. Temperatures will also decrease across the area on Friday, with eastern UT seeing the largest decrease by about 10-15 degrees as compared to Thursday afternoon highs. Moving into the weekend, our sensible weather starts to be peripherally influenced by a low pressure system settling over the PacNW, though the air mass remains quite dry. Currently, the biggest impact looks to be a cooling trend beginning Saturday, mainly across northern areas. Model guidance really starts to diverge in the upper- level pattern on Sunday, which will ultimately determine the extent of this cooling trend across the area. Ensemble members are split roughly 70-30, with 70% of members favoring a stronger cooldown on Sunday into Monday, associated with a more amplified trough. The other 30% favor not much of a cooldown at all. To further illustrate the high uncertainty, highs at KSLC on Monday range from 70F to 85F (25th to 75th percentiles). In St. George, this range isn`t quite as big, but still ranges from 92F to 100F. && .AVIATION...KSLC...Light, southeasterly winds will continue until a transition to northwesterly around 17-18z. Winds may become light and variable at times during the morning. .REST OF UTAH AND SOUTHWEST WYOMING...Light, diurnally-driven winds will prevail, aside from some gusts to 20kts out of the west across Uinta Co., WY and the western Uinta Basin after 18z. VFR conditions will prevail. && .FIRE WEATHER...High pressure will build back into the area through Thursday, bringing hot, dry, and increasingly breezy conditions. The hottest days are expected to be Wednesday and Thursday. Isolated high-based showers remain possible over the southern mountains and south-central valleys this afternoon from what moisture is left from the drying airmass. These are unlikely to produce much in the way of measurable rain, much less wetting rain. Southwest winds will gradually increase Wednesday into Thursday ahead of the next approaching storm system, strongest across southern Utah. Combined with the dry airmass, these winds will result in marginally critical fire weather conditions Wednesday and localized, low-end critical fire weather conditions on Thursday. The next storm system will then eject across southern and eastern Utah Friday. This will bring with it increasing moisture and cooler temperatures heading into the weekend. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning from 11 AM Wednesday to 10 PM MDT Thursday for UTZ131. WY...None. && $$ Cheng/Cunningham For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity