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Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
018 FXUS65 KSLC 232139 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 339 PM MDT Sun Jun 23 2024 .SYNOPSIS...Dry and hot conditions will continue across northern Utah through Tuesday as lingering moisture keeps a threat of showers and thunderstorms over southern Utah. Showers and thunderstorms can be expected across the area Wednesday before drier conditions move in late in the week. && .SHORT TERM (Through 12Z Tuesday)...High pressure is in place over Utah and southwest Wyoming this afternoon, though the ridge axis has shifted just east of the area to western Colorado. Seeing a light west to southwest flow over the area because of this, which is allowing deeper moisture over the area to roughly stay put over southern Utah. Seeing satellite derived PWs in the 0.7 to 0.9 inch range over southern Utah and in the 0.5 to 0.6 range over northern Utah and southwest Wyoming. In the more moist airmass and some lingering instability, have seen widely scattered convection develop over southern Utah with some isolated flash flooding. The threat of storms will continue into the early evening before diminishing. Meanwhile, northern portions of the forecast area are seeing quite unseasonably hot conditions with maxes running 10-15F above seasonal normals, approaching daily records in some areas. Excessive Heat Warnings and Heat Advisories remain in effect through early this evening for many northern Utah valleys. With some flattening of the ridge anticipated overnight due to a storm system moving across southern Canada, will see temperatures running a bit less hot for Monday, keeping maxes away from record values. The drier airmass will also allow for more overnight recovery, so see no need to extend heat headlines into tomorrow. Meanwhile, little change in the pattern is anticipated over southern Utah to start the work week, so the more moist airmass will remain in place, and so will the threat of afternoon and early showers and thunderstorms capable of producing heavy rain that could lead to flash flooding. .LONG TERM (After 12Z Tuesday), Issued 330 AM MDT...Tuesday looks to be the hottest day of the long term period as strong ridging across the south central to southwest CONUS continues to exert influence upon the local forecast region. Afternoon highs along the Wasatch Front once again generally range from the low 90s to a little over 100, and for Lower Washington County a bit above 105 of so. Areawide, these temperatures are around 5 to 15 degrees above climatological normal for late June. Compounded with very mild overnight lows, HeatRisk once again highlights Tuesday as a potential candidate for heat related headlines (primarily across northern Utah). However, given it looks somewhat borderline as forecast, and there`s a non-zero chance clouds could increase a bit ahead of schedule and keep temps a little better in check, will hold off on any issuance with this forecast package. In any case, as has been mentioned in several previous discussions, it will be hot out there regardless. Heat related safety should still be kept in mind, especially for those working or recreating outdoors. Stay hydrated and take frequent breaks if at all possible, and ideally wear light and loose fitting clothing. Aside from the heat, will still see sufficient lingering moisture in combination with afternoon heating to trigger isolated to scattered afternoon convection. Largely expect activity to fire off terrain and drift into adjacent valley locations, with highest coverage across southern Utah. While not anticipated to be overly widespread, those planning any recreation in rain sensitive areas should remain weather aware. Wednesday will see the first semblance of a shift in the ongoing pattern, as a trough deepening into the PacNW will help flatten and shift the ridge a bit eastward. Combination of the flattened and slightly displaced ridge along with increasing mid level moisture and associated cloud cover will help afternoon high temperatures begin to trend downward. Additionally, will see some increasing (but still fairly weak) PVA in the enhanced southwesterly flow between the deepening trough and ridge, so will see an expansion of isolated to scattered precipitation chances across the majority of the forecast region. The aforementioned Pacific trough continues to deepen a bit as it shifts inland Thursday and Friday. While guidance continues to carry some differences in just how deep and how quickly the trough advances eastward, there remains fairly good consensus that it will push a cold frontal boundary southward towards and likely into the forecast region. So far, most likely timing of this feature is later Thursday on into early Friday, with elevated precipitation chances maintained until after frontal passage and subsequent advection of some drier post-frontal air. This will result in a continued downward trend in temperatures, with Friday currently looking like the coolest day of the forecast period, with afternoon high temps generally near to even a bit below climatological normal. That said, overall deepness of the trough will impact how far south the front progresses and just how cool things get, and there`s still a decent amount of spread in guidance. For example, at KSLC for Friday the NBM 25th percentile high temperature (stronger trough scenario) is 84 degrees, and the NBM 75th percentile high temperature (weaker trough scenario) is 95 degrees. In any case, it looks like the trough will at least give the area a reprieve from some of the more excessive heat from earlier in the week. Moving into the weekend, guidance currently leans in favor of a gradual restrengthening of ridging, and thus yields a warming trend back to above normal. Most guidance also currently seems to suggest limited moisture availability, so with the subsident effect of the building ridge, precipitation chances remain limited with this forecast package. && .AVIATION...KSLC...Northwest flow at the SLC terminal should persist until the regular or slightly delayed diurnal shift. There is a low chance that convection further south of the area could push gusty outflow winds towards the terminal for a few hours this evening, with no convection anticipated directly near the terminal. Only limited mid level cloud cover is anticipated through the period. .REST OF UTAH AND SOUTHWEST WYOMING...Dry weather is expected to continue at northern Utah terminals this evening, with limited mid level cloud cover. Depending on how far north convection develops across Utah, there is a low chance (less than 20%) gusty outflow winds could push northward toward some of the northern terminals. At southern terminals, isolated to scattered convection is expected to continue into early evening. These terminals will see better odds of gusty outflow winds and lightning with anything that drifts over a terminal. After convection wanes, winds are expected to follow a more typical diurnal pattern overnight. && .FIRE WEATHER...Little change in the weather pattern is anticipated through Tuesday. Under high pressure and relatively light flow, moisture will remain trapped over southern Utah, resulting in a daily threat of showers and thunderstorms capable of producing heavy rain and gusty winds. Over northern Utah, conditions will remain dry with unseasonably hot temperatures. By Wednesday, south to southwest flow is expected to increase as a Pacific Northwest trough moves onshore, drawing the moisture over southern Utah northward across the entire state, thus increasing the threat of convection areawide. This system is expected to graze northern Utah on Thursday, bringing a front through. This would shift the flow aloft to the west, allowing drier air to move in as winds increase, bringing a threat of critical fire weather conditions to southern Utah late in the week. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning until 9 PM MDT this evening for UTZ101>105. Heat Advisory until 9 PM MDT this evening for UTZ106-107-116-118- 119. WY...None. && $$ SHORT TERM/FIRE WEATHER...Traphagan LONG TERM...Warthen AVIATION...Verzella For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity