Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
728 FXUS65 KSLC 242138 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 338 PM MDT Fri May 24 2024 .SYNOPSIS...Increasing moisture will bring a chance for rain this evening and overnight from southwest Utah to southwest Wyoming. A frontal boundary will bring widespread rain with embedded thunderstorms across much of the state tomorrow. A cool, stable airmass will shift into the area for Sunday, followed by a substantial warming trend early next week. && .SHORT TERM (Through 12Z/6AM Sunday)...Mid and high based cloud cover are sandwiched between fairly clear skies in northern and southern Utah this afternoon. Headed into the evening and overnight, increasing moisture will further enhance cloud cover and increase chances for rain production across much of central Utah while a frontal boundary continues to meander across the state. There actually looks to be a fairly large swatch of rain activity from the southwest corner of Utah (north of the Pine Valley Mountains) to southwest Wyoming. This line is expected to extend as far north as Utah/Wasatch Counties but stay south of Salt Lake City. But that said, there is around a 20% chance for rain in SLC this evening. This will also be when snow showers begin in the higher elevations of the western Uintas, where snow is expected to continue to fall through tomorrow. Accumulations above 9000 ft are forecast in the 8 to 10 inch range. Early tomorrow morning, a shortwave trough will be making its way toward the region with a frontal passage forecast during the day. Generally speaking, Saturday is expected to be a cool and soggy one. The front is expected to cross the Wasatch Front during the late morning/early afternoon hours, bringing cooler temperatures, widespread rain and embedded thunderstorms. There is little to no threats for any severe weather with this line moving through and marginal, at best, threats for small hail. The main concerns tomorrow will be with gusty winds associated with these thunderstorms. As the frontal boundary passes through eastern Utah, there`s a greater than 50% risk for wind gusts to exceed 40 mph especially after 3 pm. South of the boundary, expect breezy westerly winds throughout much of the day tomorrow. Gusts of 30 to 40 mph are expected especially across Bryce Canyon and the Grand Staircase, but we are shy of wind advisory criteria and will not be issuing at this time. High temperatures Saturday across many valleys will be in the modest 60`s. Even the greater St. George area will feel a slight cooling; climbing just over the 80 degree mark tomorrow. Flow will remain northwest to west Saturday night into Sunday and allow for a general drying trend. A 20% or less chance for additional rain showers will exist during this period as a result. .LONG TERM (After 12Z/6AM Sunday), Issued 309 AM MDT... Beginning on Sunday, a return to summer-like weather will begin to make an appearance across Utah and SW Wyoming in the wake of our departing storm system with temperatures beginning to rise. A more substantial increase in temperatures will begin on Monday, when temperatures will rise ~10F across the north and ~5F across the south. Deterministic and ensemble guidance is in good agreement in building a high pressure ridge across the region through early next week, and this feature will be responsible for the warming/drying trend. The warmest day of the period (and the year to date) is now most likely on Tuesday. This is when high temperatures will soar into the upper 90s across Lower Washington County to the upper 80s across the Wasatch Front. Latest NBM shows a 27% chance of reaching 90F at SLC on Tuesday. With enough southerly downslope influence and enough sunshine, this probability could be a bit conservative. Forecast certainty does begin to wane slightly by midweek, as differences emerge regarding the evolution of the mid-level ridge as well as potential interactions with an incoming PacNW trough, with notable strength and timing differences apparent across the solution space. By Wednesday, 80% of the solution space shifts the ridge axis off to the east, suggesting a slight cooling trend will emerge. As we head into the Thursday-Friday timeframe, around 1/4 to 1/3 of the solution space drops a trough across the Northern Rockies, with a similar sliver of the remaining solution space representing either zonal flow or the ridge simply staying put. Through this analysis, we see 3 possible forecast outcomes in the Thursday to Friday timeframe. We`ll call scenario 1 the outcome that keeps the ridge in place; and this would imply maintenance of warm/dry conditions. Scenario 2 with its transition to the zonal flow regime would suggest temperatures cooling back down near seasonal normals across the north along with little change in temperatures across the south. Additionally, a low chance for a few showers/storms across northern Utah/SW Wyoming may accompany said pattern shift. Finally, scenario 3 with the stronger Northern Rockies trough would suggest temperatures cooling to slightly below normal across northern Utah/SW Wyoming with only modest cooling across southern Utah, along with higher chances for showers across the north. At present, all 3 scenarios are essentially equally possible forecast outcomes, and the official blended/calibrated forecast falls more in line with scenario #2 and its zonal flow regime. As we get closer to this period of greatest uncertainty, we`ll continue to monitor trends to observe which one of these outcomes becomes the most dominant outcome. && .AVIATION...KSLC...VFR conditions will persist for the KSLC terminal through the period. Winds will be variable this afternoon as a northerly lake breeze is countered by southerly outflow from showers south of the terminal. A predominant southerly flow establishes this evening/overnight, but VCSH could create more brief variability in the winds. Expect CIGs to develop near ridgetop creating some mountain obscuration overnight. .REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist for most terminals this evening and overnight. High based showers across central Utah will create some gusty outflow leading to variable winds with a mean southerly flow, otherwise. CIGs lower overnight with showers becoming more numerous across central Utah with intermittent mountain obscuration. Winds predominantly remain southerly with mostly dry conditions across southern Utah. && .FIRE WEATHER...Increasing statewide moisture tonight is forecast to lead to further cloud cover and increasing risk for rain showers. Wetting rains are expected to be highest across central Utah this evening which will inch northward overnight. There is risk for isolated gusty outflow winds or microburst winds in any thunderstorms that may develop. Headed into tomorrow, widespread rain and thunderstorms are forecast along and north of I-70. The highest risk for gusty winds looks to be in eastern Utah as the frontal boundary passes, where there`s a greater than 50 percent likelihood for wind gusts to exceed 40 knots. These winds are expected to be strongest between approx 1500 hrs and 1900 hrs. South of the boundary, look for breezy westerly winds. By Sunday, conditions are forecast to dry out across the region with a west to northwest flow expected. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ NDeSmet/ADeSmet/Mahan For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity