Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
859 FXUS65 KSLC 250938 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 338 AM MDT Sat May 25 2024 .SYNOPSIS...A low pressure system will bring widespread rain with embedded thunderstorms across much of the region. A relatively cool and stable airmass will spread across the area Sunday, followed by a substantial warming trend early next week. && .SHORT TERM (Through 12Z/6AM Monday)...A multi-faceted upper trough will cross the forecast area today, bringing fairly widespread precipitation across northern and central Utah, along with cooler temperatures across the region. Initially this morning a SW-NE oriented baroclinic zone stretches from roughly Cedar City to Vernal, and has been the focus for several rounds of showers overnight. A shortwave feature noted in satellite imagery crossing the southern Great Basin will ride along this boundary this morning, maintaining shower activity in the vicinity of the boundary through sunrise. Attention then turns to an upstream shortwave trough currently crossing the northern Great Basin and inducing numerous showers across northern Nevada. This wave will amplify a bit as it translates across the forecast area today. Showers will increase within a region of large scale ascent across northern Utah through this morning, with most CAM guidance suggesting at least a broken line of convection surges through northern and central Utah late this morning through early afternoon, followed by more scattered band of showers later in the afternoon. Small hail, lightning, gusty winds to 45 mph, and lightning will be common with the stronger cells. If enough clearing develops ahead of the convective line allowing surface heating and sufficient instability, it`s not out of the question outflow along localized portions of the line could exceed 50 mph and approach severe thresholds, particularly across the western Uinta Basin and Castle Country/San Rafael Swell. Any lingering convection should wind down by sunset as the parent wave moves east of the area. Snow levels through the event will generally remain near or above 9000 feet, and could see some accumulation along the higher ridgelines of the Wasatch as well as across the western Uintas. With abundant cloud cover and precipitation across northern and central Utah today, temperatures will trend considerably lower and run roughly 10F below climo, with maxes remaining confined to the low 60s along the Wasatch Front. The cooling trend across southern Utah will be less pronounced, as temperatures trend roughly 5F cooler today. Mid level ridging will begin to amplify upstream in the wake of the departing storm system Sunday, leaving the forecast area with a relatively stable northwest flow. The airmass will modify as heights slowly rise, allowing max temperatures across northern Utah to trend 6-10F warmer, remaining a few degrees below climo. Temperatures across southern Utah will trend close to 5F warmer, allowing max temps to approach 90F in the St George area Sunday afternoon. .LONG TERM (After 12Z/6AM Monday)...A sharp warmup will be underway on Memorial Day across Utah and SW Wyoming as a transient, albeit strengthening mid-level ridge axis will traverse eastward across the region. When compared to today (Saturday), expect a very noticeable nearly a 20F warmup on Monday across northern and central Utah, with about a 10F warmup across southern Utah. NBM probability of 90F at SLC has climbed to 38%, now centered on Wednesday. The mean first 90F day in SLC is June 8, so we`re not too far off the mark should 90F be reached. A well- clustered model consensus with high forecast confidence early in the week then begins to wane as the above- mentioned ridge axis exits to the east by Tuesday-Wednesday, with increasing deep-layer SW flow developing on Tuesday as an area of low pressure moves into coastal British Columbia. As this evolution transpires, additional warming will be in store for Tuesday, with temperatures reaching the mid to upper 80s across the Wastach Front, and the upper 90s across Lower Washington County. We can`t rule out an isolated shower or thunderstorm by Tuesday afternoon, mainly over northern Utah and SW Wyoming. Similar to yesterday`s forecast, uncertainty begins to emerge by midweek, with the greatest source of uncertainty regarding the track, strength and timing of the aforementioned low. We now see a clearer signal for the emergence of two forecast scenarios appearing by Wednesday and carrying us through early next weekend, and those two scenarios are a ridge vs a trough scenario, with a slight (about 60% of the solution space) nudge towards the trough scenario. Should the ridge remain in place, warm, mainly dry conditions would be the most likely outcome through the remainder of the forecast period. The trough solution would bring a mid to late week reduction in temperatures back closer to average (or even below average in the stronger trough solutions) with periods of showers across northern Utah and SW Wyoming as well as gusty winds on the periphery of the trough. Given the uncertainty and the nearly equally divided model solution space, it`s too early to pick a ridge or trough solution as a most likely outcome. It is worth mentioning that models are trending very gradually towards the trough idea, and this is supported by the most recent runs of deterministic, global models as well. Finally, this trend is also reflected in the official forecast which shows gradual cooling Thursday and Friday. && .AVIATION...KSLC...A disturbance and associated cold front will sweep across the terminal this afternoon bringing a myriad of impacts. First, gusty S winds (15-25kts) anticipated this morning with showers in the vicinity. Line of showers with embedded thunder expected to move across the terminal between 17Z-20Z, complete with gusty, erratic outflow winds, lightning and perhaps small hail. Can`t rule out brief reductions to MVFR (25% chance) with a 10%, with a chance for brief IFR conditions. In the wake of this wave, isolated to scattered showers and isolated thunderstorms linger through about 03Z. Wind direction forecast is highly uncertain after 18Z due to the shower/storm activity, but confidence increases in the emergence of S winds around 02Z. .REST OF UTAH AND SOUTHWEST WYOMING...Disturbance and associated cold front will move across Utah and SW Wyoming this afternoon. In advance of these features, band of showers will continue across central and NE Utah this morning, with pockets of mountain obscuration. Clusters of showers and thunderstorms will then move across central and northern Utah as well as SW Wyoming later this morning through the afternoon hours. This activity will produce gusty, erratic outflow winds, brief reductions in CIG/VIS to the IFR category, lightning and small hail. This activity will gradually diminish this evening, leaving tranquil conditions overnight. && .FIRE WEATHER...A low pressure system will bring widespread showers accompanied by wetting rains to much of northern, central and southwest Utah today. Scattered thunderstorms can also be expected. Precipitation will be more scattered in nature across south central and east central Utah. With the passage of this system, gusty winds can also be expected across the western Uinta Basin and the San Rafael Swell region. A more stable airmass behind this system will spread across the region Sunday which will keep temperatures several degrees below normal. A substantial warming trend will begin Memorial Day, and continue through midweek, pushing temperatures 10 degrees above normal by Tuesday. This airmass will remain in place Wednesday as southwesterly flow increases, resulting in very dry and breezy conditions Wednesday afternoon. A mostly dry cold front is expected Thursday cooling temperatures a bit and switching winds to the northwest. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ Seaman/ADeSmet For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity