Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
497 FXUS65 KSLC 230930 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 330 AM MDT Sun Jun 23 2024 .SYNOPSIS...Dry and hot conditions will continue across northern Utah through Monday...with the threat of showers and thunderstorms across central and southern Utah. By Wednesday, showers and thunderstorms can be expected statewide. && .SHORT TERM (Through 12Z Tuesday)...With the upper level ridge centered over the southern Plains/southern Rockies over the next several days and the continued active northern stream, it`ll be a bit of rinse and repeat each day. Looking at surface dewpoints across southern Utah, lower terrain areas continue to see elevated dewpoints in the 40s to 50s. No surprise that precipitable water plots show values between 0.75-1.25" across southern Utah. Sufficient instability will exist across southern and eastern Utah today for more widespread convection than Saturday. With slower storm motions, expect the threat of flash flooding will be elevated today, especially from Zion to the Buckskin/Paria Narrows area and the Capitol Reef area. With less deep layer shear, the threat of severe convection is lower than the last few days. Meanwhile, across northern Utah, an increasing dry and hot airmass will be in place. Expect temperatures in the upper 90s to low 100s across the Wasatch Front and Cache Valley. Added a heat advisory for the Cache Valley with this package and kept the remainder of the heat headlines in place. For Monday, PWs remain elevated across much of southern and eastern Utah with continued slow storm motions. Expect another round of convection with the main threat continuing to be flash flooding. Convective coverage may be a bit less than Sunday. Temperatures will be a bit cooler across northern Utah Monday afternoon and evening...and thus...currently do not have any heat products out. Main messages for the short term forecast is be mindful of the very hot temperatures and avoid activities during peak heating across northern Utah. For southern Utah, consider avoiding slot canyons, dry washes and other flood prone areas, especially for locations near the Utah/Arizona border. .LONG TERM (After 12Z Tuesday)...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...Enhanced southerly winds expected to see a somewhat delayed diurnal shift, with guidance suggesting a switch to northwest between ~19Z-22Z Sunday. There is a low chance (less than 20%) that convection further south of the area could push gusty outflow winds towards the terminal late afternoon into the evening. Convection is not currently anticipated directly near the terminal, however. Winds then favored to switch back southerly ~03Z-05Z. Only limited mid level cloud cover anticipated through the period. .REST OF UTAH AND SOUTHWEST WYOMING...Generally dry weather is anticipated at northern Utah terminals Sunday, with fairly limited mid level cloud cover. Depending on how far north convection develops across Utah, there will be a low chance (less than 20%) gusty outflow winds could push northward towards some of the northern terminals. At southern terminals, a bit more moisture in combination with daytime heating will yield isolated to scattered convection. These terminals will see better odds of gusty outflow winds in addition to lightning and briefly reduced conditions with anything that drifts over a terminal. Convection wanes moving later into the evening, with winds following a more typical diurnal pattern overnight. && .FIRE WEATHER...With a lack of cold front to scour out the modified tropical moisture in place over the last few days across portions of southern Utah, the threat of showers and thunderstorms will continue Sunday into Monday. This will ease minimum humidities a bit higher averaging around 20-30% for lower terrain areas of southern Utah, 25-35% for higher terrain areas. Meanwhile across northern Utah, humidities will continue to be quite low, with west central and northwest Utah seeing minimum humidities as low as the single digits. The threat of convection will lower Tuesday. By Wednesday, an upper level system crossing into the Pacific Northwest will bring a nearly statewide threat of convection, with an improvement in humidities. A dry slot across western Utah may bring gusty winds and low humidities Thursday, potentially bringing critical fire weather conditions to locations with receptive fuels across western Utah. As a cold front crosses the state Friday, more widespread critical fire weather conditions are possible across much of southern Utah. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Warning from 9 AM this morning to 9 PM MDT this evening for UTZ101>105. Heat Advisory from 9 AM this morning to 9 PM MDT this evening for UTZ106-107-116-118-119. WY...None. && $$ Kruse/Warthen For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity