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Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
201 FXUS65 KSLC 072051 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 251 PM MDT Sun Jul 7 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 Tuesday)...It`s an extremely dry and breezy day across southern/central/eastern Utah today. RH values are well below 5 percent in several spots and even observed at 1 percent in a few spots. Northwest and westerly winds with gusts of 25 to 35 mph are observed across Castle County, the Central Mountains and across southern Utah. These winds are expected to continue until near sunset before they generally diminish. Some canyon winds in lower Washington County are expected overnight with gusts around 30 mph along I-15. An excessive heat warning has gone into effect this morning for lower Washington County, Zion Canyon and Glen Canyon NRA. This warning has been extended through midnight Friday as heat conditions and overnight recoveries in these areas are not expected to improve. Temperatures tomorrow are forecast to slightly climb across northern Utah as we continue to lie on the eastern edge of ridge of high pressure. .LONG TERM (After 12Z/6AM Tuesday), Issued 411 AM MDT... Little change in the forecast compared to the past few forecast cycles as this portion of the forecast will continue to be dominated 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 Tuesday, model consensus places the center of the ridge axis across the Western Great Basin, with the ridge then shifting only very so slightly eastward to be centered over east- central Nevada by Wednesday. The ridge is then expected to weaken only slightly while continuing to propagate very slowly eastward through Saturday. There remain a small subset of the ensemble members keeping the ridge in place through Sunday or even early next week, so we can`t discount the possibility that extreme heat could linger a bit longer. We do see hints of this showing up in the temperature forecasts, as temperatures are likely to reach or exceed 100F in SLC one day later now, extending into Monday. Given the anomalous nature of the ridge relative to climatology and its slow eastward 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 Wednesday- Monday, when probabilities for reaching this threshold are at least 75%. We even see 107F (SLC`s all-time record high) in the 75th percentile of the MaxT distribution on Friday. Low temperatures during the peak of the heatwave will range from the mid-70s to near 80F in SLC. Relief will be tough to find even for the typically cool high elevation valleys such as the Bear River Valley, Park City and Evanston where several days with highs in the low 90s are likely. Lows here, however, will dip into the 50s, offering a brief reprieve. 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 look to the horizon to gauge both the potential for some increase in moisture and relief from the heat. Ensemble forecast systems remain in good agreement regarding when the first hints of increased total column moisture will arrive, with consensus continuing to suggest increased moisture will reach SW Utah by Saturday before overspreading the remainder of Utah and SW Wyoming by Monday, thanks to the development of deep-layer S-SW flow around the departing ridge. A cross-section of the atmosphere reveals that much of the increase in moisture will be relegated to the mid- levels, especially initially, although at least some modest increase in low-level moisture is forecast, especially over SW Utah by next weekend and early next week. Thus, the 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 Friday and especially Saturday across southern Utah, with this potential spreading into central Utah by next Sunday. Initially, main threat with this activity will be dry lightning, and this is concerning following an extended hot, dry stretch as any lightning will have the potential to create 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...A hot, dry and windy pattern remains will bring critical fire weather concern across central and southern Utah today. Wind gusts of 20 to 35 mph and very dry air, less than 5 percent in some cases, are observed. Much of the flow is northwesterly with a nod to a westerly wind in a few locations. These conditions are expected to persist until the sun sets this evening. At that point winds will ease under 20 mph and drop off overnight. RH recoveries overnight tonight are not great, at 15% to 25% across Color Country, the Grand Staircase, Henry Mountains and the Mojave Desert. Similar, or even poorer overnight recoveries can be anticipated for the next several days across much of the state. The positive news here is that the pressure gradient will relax tomorrow. Wind and wind gusts are not expected to be as strong as they are expected to be today. Flow will remain generally northwesterly but only a portion of Color Country and Central Utah Mountains have about a 30% chance for seeing 30 mph wind gusts or stronger. Lighter winds are expected tomorrow across southern and central Utah, around 20 mph. Mid to late week, a center of high pressure is forecast to gradually meander closer to Utah which will only assist in warming temperatures across the region. A few bouts of moisture continue to show up in forecast models over the weekend, but location placement and amounts of moisture is still very uncertain at this time. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...Excessive Heat Watch from Wednesday morning through Friday evening for UTZ101>107-115-116-118-119-122-128. Red Flag Warning until 9 PM MDT this evening for UTZ482-489-493- 494-496>498. Excessive Heat Warning until midnight MDT Friday night for UTZ123-124-131. WY...None. && $$ SHORT TERM...NDeSmet LONG TERM...ADeSmet AVIATION...Cheng FIRE WEATHER...NDeSmet For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity