Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
380 FXUS65 KSLC 152135 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 335 PM MDT Sun Sep 15 2024 .SYNOPSIS...Winds will become strong and gusty by Monday ahead of an approaching fall-like storm system, with enough instability for some strong to severe thunderstorms. The trough will cross the area late Monday into Tuesday, bringing showers, primarily focused over northern Utah, along with much cooler temperatures for the entire area. && .SHORT TERM (Through 12Z Tuesday)...Utah and southwest Wyoming are under an increasing southwest flow aloft in between a ridge over the central United States and a broad trough moving onshore along the Pacific coast. In this flow, have seen increasing moisture with instability being provided by shortwave energy ejecting out ahead of the low. Convection this afternoon has been scattered, high based, and primarily focused over the northern half of the forecast area. Most of the convection will tend to diminish this evening, with some storms continuing later over far northwest Utah where better jet support exists. Temperatures today remain on the mild side, near seasonal normals over southern Utah but in excess of 5F above climo over northern Utah. The Pacific low will slide into the Great Basin by tomorrow afternoon, and southerly flow aloft will increase further. Flow aloft is expected to be in excess of 50 kts over western Utah, where ensembles indicate an 80 to 90 percent chance of wind gusts exceeding 40 mph tomorrow afternoon. Going Wind Advisory covers this threat well. Elsewhere, some isolated wind gusts to 40 mph will be possible, but should not be long lived enough to warrant any headlines. Position of the upper level jet on the front edge of this trough will put much of Utah, particularly northern and eastern portions, under an enhanced risk for more organized storms, with some severe storms possible. Limiting factor for storms tomorrow will be moisture, as a dry slot will limit coverage over at least southwest Utah, but instability should be sufficient. By late Monday, the trough will begin its slide across northern Utah, bringing more widespread showers to that portion of the area. .LONG TERM (After 12Z Tuesday), Issued 417 AM MDT...A continuation of a net northeasterly translation of the anomalously deep upper low in place will occur Tuesday, with the core progged to be over northwestern Wyoming by 00z Wednesday (filling as it lifts). Through that period the cold core will be spreading across the northern tier of the forecast area during the day Tuesday aiding increased low level instability for a maintenance of showers/storms across the northern third...most likely north of the I-80 corridor. Much cooler temps associated with/post passage into the midweek period, some 10-15 degrees below climo forecast attm. Providing the kicker for this first upper low will be a trailing upper low that will take a further west/south trajectory as it deepens along the Pac Coast and western Great Basin Wednesday, prior to lifting ENE across the forecast area Thu-Fri (filling whilst once again). On Wednesday the focused forcing will be tied to a strengthening deformation axis centered to the west over Nevada, but subtle differences in placement within ensembles of such a detail remain. Consensus maintains chance showers focused generally over northern/western portions (Wed) tied closest to this feature however, and going forecast reflects this. Thereafter additional shower/storm potential appears to be tied along and ahead of the mid level axis passage and cold core as the trough progresses ENE across the region through Friday. Primary takeaway with this trough is a reinforcement of the unseasonably cool airmass, as only modest at best precip is expected areawide, prior to a drying trend from W-E to enter into early next weekend. Globals continue to advertise a third upper low translating southeast into the area later next weekend into early next week. Lots of uncertainty in amplitude/track/evolution of this feature so can`t resolve much more than yet another reinforcement of cooler than normal conditions attm. && .AVIATION...KSLC...Gusty southerly winds with 25-30kts will continue, decreasing in speed after 02z. Isolated to scattered showers and thunderstorms will continue to develop late this afternoon and into the early evening, with the best chance for thunder over the terminal between 23-02z. Gusty southerly winds are expected once again tomorrow (Monday). .REST OF UTAH AND SOUTHWEST WYOMING...Gusty southerly to southwesterly winds will continue, decreasing in speed after roughly 02z. Scattered showers and thunderstorms (north of KCDC-KBCE) will persist through roughly 03z, with a few heavier showers possible through 07-08z across northern UT and southwestern WY. These storms will be capable of producing gusty and erratic outflow winds. Stronger southerly winds will return Monday afternoon with another chance for showers and thunderstorms. && .FIRE WEATHER...Seeing some high based showers and storms developing this afternoon, primarily over northern and central Utah. Any storms that develop will be capable of producing gusty and erratic thunderstorm winds through the evening. As a Pacific trough approaches tomorrow, winds will continue to increase over the area, becoming strong and gusty, particularly over western Utah. Dynamics will also become increasingly favorable for the develop of showers and thunderstorms, particularly over northern and eastern Utah, with some strong storms possible. RH values are expected to stay at or above 20 percent Monday afternoon, which will limit fire weather concerns somewhat. The storm system will cross the area late Monday into Tuesday, bringing additional showers to northern Utah and much cooler air across the area. The cooler temperatures will persist for several days. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Wind Advisory from noon to 9 PM MDT Monday for UTZ115-122. WY...None. && $$ SHORT TERM/FIRE WEATHER...Traphagan LONG TERM...Merrill AVIATION...Cunningham For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity