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Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
812 FXUS65 KSLC 062000 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 200 PM MDT Sat Jul 6 2024 .SYNOPSIS...High pressure will gradually shift eastward over the next seven days, bringing increasingly warm temperatures first to southern Utah this weekend, and then northern and central Utah Wednesday. && .SHORT TERM (Through 12Z/6AM Monday)...Utah will continue to sit on the eastern periphery of a ridge of high pressure the remainder of the weekend. Warm and dry conditions are forecast to continue with northwest flow persisting. Afternoon breezes are forecast to increase once more across eastern Utah under this regime with winds in the 10 to 20 mph range and gusts exceeding 30 mph. Temperatures are forecast to be pretty similar tomorrow when compared to today statewide. Excessive Heat Warnings will go into effect starting tomorrow for lower Washington County, Zion NP and Glen Canyon Recreation Areas. .LONG TERM (After 12Z/6AM Monday), Issued 441 AM MDT... Long term portion of the forecast will continue to be punctuated by potentially dangerous, excessive and prolonged heat. Global deterministic and ensemble systems remain in very good agreement regarding the strength, positioning and progression of the ridge through the period, the feature responsible for the excessive heat. On Monday, model consensus places the center of the ridge near Death Valley, CA migrating to over southern Nevada on Tuesday before finally propagating to near/over Utah by Wednesday. The ridge is then expected to weaken slightly while remaining overhead through Friday, with a subset of the ensemble solution space keeping the ridge in place through the weekend. Given the anomalous nature of the ridge relative to climatology and its slow progression, surface temperatures will challenge record values for several days, adding to the cumulative effects of the hazards associated with this heatwave. Overnight cooling will be limited as well. The bottom line is that the cumulative effects of this excessive heat will place significant stress on people and pets, particularly those without adequate cooling and those that spend significant time outdoors, adding to the vulnerability. Avoid strenuous outdoor activities during the hottest time of the day, drink plenty of water and limit exposure to the sun. Temperatures are likely to reach or exceed 110F in St. George from Sunday through Friday, when probabilities for reaching or exceeding 110F are above the 75th percentile. Low temperatures during this period will range from the upper 70s to the mid 80s. For SLC, temperatures are likely to reach or exceed 100F from Tuesday-Sunday, when probabilities for reaching this threshold are at least 75%. Even typically cool high elevation valleys such as the Bear River and Evanston will experience several days with highs in the low 90s. Low temperatures during the peak of the heatwave will range from the mid-70s to near 80F in SLC. Thus, this heatwave will rival past heatwaves both in terms of duration and intensity. EFI values remain elevated and standardized anomaly 700mb temperatures reach or exceed those in the model climate, especially over SW Utah early in the week. We continue to monitor for the potential for some increase in moisture and relief from the heat. Ensemble consensus is coming into better agreement regarding these prospects, with the first signs of an increase in total column moisture reaching SW Utah by Saturday before overspreading the remainder of Utah and SW Wyoming by Monday. A cross-section of the atmosphere reveals that much of the increase in moisture will be relegated to the mid-levels, although at least some modest increase in low-level moisture is forecast, especially over SW Utah by next weekend. First signs of the moisture increase will be manifest in the form of mid/high level clouds, with the first appearances of isolated terrain-based thunderstorms arriving by Saturday across southern Utah. Initially, main threat with this activity will be dry lightning, and this is concerning following an extended hot, dry stretch as the lightning will add to the potential for new wildfire starts. && .AVIATION...KSLC...The SLC terminal will see VFR conditions through the evening with mostly clear skies. Northwest winds are expected to shift to the southeast between 03Z and 05Z. .REST OF UTAH AND SOUTHWEST WYOMING...Except for areas downwind of fires, the airspace will see VFR conditions through the evening with mostly clear skies. With strong northwest flow aloft, some areas will see breezy conditions continuing through the early evening, with generally light winds otherwise. && .FIRE WEATHER...An extremely dry airmass will remain in place over Utah through the next 7-10 days, bringing afternoon relative humidity values down into the low-to-mid teens to single digits across a large majority of the area. A shortwave trough is expected to scrape through the area through the next 24-36 hours, bringing increasingly strong winds out of a northwesterly direction. Through the rest of today, the strongest winds will be confined to the northern half of Utah, combining with critically dry humidity and fuels to warrant Red Flag Warnings. Overnight humidity recoveries are expected to be poor across most areas outside of the northern third of Utah tonight, with values only recovering to around 15 to 25 percent. Tomorrow, winds increase in speed and areal coverage across the southern half of Utah with many more areas reaching critical fire weather thresholds. As such additional Red Flag Warnings will go into effect for Fire Weather Zones 497 and 498 starting tomorrow at 1200. Overnight recoveries will begin to increase by about 10 percent across the northern half of the area, however, the southern half of Utah will continue to see recoveries around 15-30 percent. Heading into next week, temperatures will become increasingly hot as a long duration heatwave begins spreading over Utah. Temperatures will rise to around 10 to 15 degrees above average for this time of year for much of the area, with humidity values continuing to bottom out in the teens to single digits. There is currently a low to medium chance of moisture building into the region late in the week, which may bring an initial threat of dry lightning to the southern Utah mountains. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Red Flag Warning until 9 PM MDT Sunday for UTZ482-489-493-496. Excessive Heat Warning from 9 AM Sunday to 9 PM MDT Wednesday for UTZ123-124-131. Red Flag Warning from noon to 9 PM MDT Sunday for UTZ494-497-498. WY...None. && $$ NDeSmet/Webber/ADeSmet/Traphagan For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity