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Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
456 FXUS65 KSLC 081024 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 424 AM MDT Mon Jul 8 2024 .SYNOPSIS...High pressure will gradually shift eastward over the next seven days, bringing increasingly warm temperatures first to southern Utah early in the week, then spreading across the remainder of Utah and southwest Wyoming. && .SHORT TERM (Through 12Z/6AM Wednesday)...Mid level ridging centered across central California continues to induce a deep layer north-northwesterly flow downstream across the eastern Great Basin/Colorado Plateau region. This flow has allowed slightly cooler air to remain in place across northern Utah/southwest Wyoming, and despite the airmass modifying a bit trending temperatures slightly warmer, daytime highs will remain near to slightly above climo today. Meanwhile, far southwestern Utah remains under the influence of a very hot airmass associated with the upstream ridge. Temperatures across lower Washington County will cool slightly today, but still approach the 110F mark around St George and Zion Canyon. The upstream ridge will nudge eastward Tuesday, trending max temperatures up 3-5F across the forecast area. This will push daytime temperatures into the upper 90s across lower valleys of northern/central Utah including the Wasatch Front/Cache Valley. Meanwhile St George/Zion Canyon, where an Excessive Heat Warning is in effect, will exceed the 110F mark Tuesday afternoon. .LONG TERM (After 12Z/6AM Wednesday)...High confidence continues to be maintained on the forecast pattern from midweek on into the start of the weekend, with the dominant influence coming from an anomalously strong ridge of high pressure characterized by H5 heights around 2 sigma above normal. This ridge will initially be centered from the Desert Southwest into east Nevada and west Utah Wednesday, gradually migrate northeastward and become centered more or less atop Utah by Friday, and then very slowly begin shifting east through the weekend. With H7 temps generally about 18C to 22C, almost all of the forecast region will be looking at surface temperatures challenging record values for several days. Given the slow progression of the ridge, the cumulative day-to-day effect of both hot daytime temperatures and little night time relief due to very mild overnight lows will pose dangerous. The overall message remains the same that heat safety will be critical over the coming days. Drink plenty of fluids, and avoid outdoor activities during the hottest portions of the day if at all possible. If not, limit exposure by taking frequent breaks (ideally in an air conditioned location) and by wearing lightweight and loose fitting clothing. Learn to identify signs of heat exhaustion and heat stroke and appropriate actions to take accordingly. Never leave children or pets in unattended vehicles. While there are many types of hazardous weather, heat is the number one cause of weather related fatalities. Digging into forecast temperatures a bit more shows some impressive numbers. For KSLC, NBM probabilities show a greater than 95% chance to see highs exceed 100F Thursday, Friday, and Saturday, and a greater than 70% chance as well for Wednesday and Sunday. That said, it would take 6 or more days (at KSLC specifically) to crack the top 10 runs of 100F or more, and for most other days the odds fall to around a 30% chance. Unsurprisingly, the day to day spread is also fairly tight, with 25th percentile values of 103F and 75th percentile values of 106F Thursday through Saturday when the heat looks to peak. NBM probabilities carry around a 10% to 15% chance to hit or exceed 107F at KSLC Friday and Saturday, which marks the all- time record high for KSLC. For KSGU, Wednesday through Friday NBM probabilities carry around 80% to 90% chance for daily highs exceeding 110F, falling to around 60% chance by Saturday. For the moment, the forecast shows a very low (but still non-zero) chance of breaking the all-time Utah state heat record of 117F. Elsewhere around the area, deterministic forecast values are quite anomalously hot as well. This includes higher elevation valleys from the Wasatch Back to the Bear River Valley as well as southwest Wyoming, which will see afternoon highs from the upper 80s to low/mid 90s, though will see a bit more relief overnight with cooler lows. As early as Saturday, the ridge may begin to shift far enough east that it in addition to a trough approaching the Pacific coast may help advect some mid level moisture into the area within stronger southerly flow. As a result, will see some isolated to scattered shower/thunderstorm chances creep back into southern Utah. That said, the likely higher based nature to any convection will limit wetting rain chances, and may actually manifest as more of a dry lightning threat. By Sunday and Monday, ensemble consensus shows PWAT values pushing back above 100% of normal for mid July (generally 0.50" to 0.80" or so), and diurnal thunderstorm chances creep northward accordingly. Temperatures by Sunday also look to begin to fall from the peak of the heatwave as the ridge shifts, though temperatures will still remain quite hot all things considered. Some guidance also suggests the ridge may be more stubborn to shifting, in which case lower PoPs and more prolonged heat will be possible, but for now opted to keep NBM values with the aforementioned forecast logic. && .AVIATION...KSLC...No significant weather expected at the terminal, with VFR conditions and clear to mostly clear skies persisting. Winds anticipated to follow typical diurnal directional pattern with southerly drainage flow shifting northwesterly ~18Z Monday, and back southerly ~04Z thereafter. .REST OF UTAH AND SOUTHWEST WYOMING...Largely expect a quiet TAF period with most terminals seeing a continuation of clear to mostly clear skies and VFR conditions. The one exception will be potential for some smoke/haze related obscurations at any terminals downwind of area fires, particularly stronger and larger ones with more notable plumes. High resolution guidance suggests south central Utah as the most likely area to see any such smoke/haze advection. Winds anticipated to more or less follow something of a typical diurnal directional pattern. && .FIRE WEATHER...A very dry (north) to extremely dry (south) airmass will remain in place throughout the upcoming week, resulting in very low daytime RH and marginal to poor overnight recovery across most zones. A strong area of high pressure centered over California will maintain northerly flow across the area today and again Tuesday. Winds will not be quite as strong as what was observed over the weekend, however gusts in the 20-25 mph range can be expected across exposed areas of the central and southern mountains along with the western valleys. With these lighter winds, conditions are expected to remain just below critical fire weather criteria, with isolated pockets of critical fire weather conditions possible in central and southern Utah. The high centered over California will slowly move east, becoming centered across the region during the middle to latter portion of the week. The resultant warming trend will push high temperatures near daily records, and in some cases may challenge all time records. The extended nature of these record challenging temperatures will create potentially dangerous heat for those with prolonged exposure. By late in the week into next weekend, confidence is increasing in high based moisture spreading into at least southern Utah, and potentially points north, resulting in a chance for high based showers and thunderstorms as early as Friday afternoon. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Watch from Wednesday morning through Friday evening for UTZ101>107-115-116-118-119-122-128. Excessive Heat Warning until midnight MDT Friday night for UTZ123-124-131. WY...None. && $$ Seaman/Warthen For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity