546 FXUS65 KRIW 081005 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 405 AM MDT Tue Jul 8 2025 .KEY MESSAGES... - Very hot conditions with widespread 90s and some locations getting close to the triple digit mark today and Wednesday. The lowest elevations of the Bighorn and Wind River Basins have a 40-70 percent chance of 100 degree highs Wednesday. - Elevated fire weather conditions will be widespread today and Wednesday as well. Wind gusts of 15 to 25 mph is expected today. There is a 20-40 percent chance of wind gusts over 25 mph across southern portions Wednesday afternoon. - Isolated virga showers will also be possible today and and Wednesday. Wind gusts of 55 to 60 mph will be the main threat from any shower that forms. - A 20-40 percent chance of showers returns late Thursday afternoon into Friday morning for areas along and east of the Continental Divide. && .DISCUSSION... Issued at 137 AM MDT Tue Jul 8 2025 An upper level ridge, from a strong Four Corners high, will continue to build over the region today. This will lead to 90 degree temperatures returning for areas east of the Divide as well as across portions of Sweetwater County. Greybull and Worland could reach 100 degrees. Very dry and elevated fire weather conditions will be in place across much of the CWA, with critical RH values (dropping as low as 7 to 10 percent) occurring for most areas. Wind gusts of 20 to 25 mph is expected through the afternoon, with a slight exception. A weak shortwave will move over far western portions and the Star Valley early this morning and make its way over northwestern portions later this morning into early afternoon. Wind gusts of 25 to 30 mph will occur over the mountains as a result of the trough passage. Additionally, isolated virga showers will be possible, mainly over southern portions of the Bighorn Basin, the southern end of the Absarokas, the northern end of the Wind River Mountains and the Wind River Basin. Stronger wind gusts will be possible as a result from these showers, with gusts of 55 to 60 mph certainly possible due to the large dewpoint depressions that will be in place. Thus, will not be issuing any Red Flag Warnings as it does not look like wind gusts of 25+ mph will be widespread. The ridge will shift eastward over the Cowboy State tonight into Wednesday, leading to 500mb heights of 590 to 594dm and 700mb temperatures of 16C to 19C. Needless to say, this will continue the hot temperatures and elevated fire weather conditions. Winds continue to look marginal for any fire weather highlights. The atmosphere should be capped for most areas, however isolated virga showers will be possible again late in the afternoon into the evening. Sweetwater County looks the most likely location at this time, due a lead shortwave that will move over the county from northern UT. Wind gusts of 55 to 60 mph will again be possible, due to the inverted-V sounding profiles in place. A remnant low will approach the area Wednesday evening, as it moves over southern ID. The aforementioned lead shortwave will be ahead of this system as the low tracks eastward Wednesday afternoon. Increasing chances for showers and thunderstorms will become possible over western portions through the evening as the cap weakens due to the loss of diabatic heating and the low reaching the ID/WY state line. These chances spread east of the Divide after 06Z, mainly over central portions of the CWA and on the north side of the low. Precipitation chances will continue to shift eastward through the morning and exit most of the forecast area through the afternoon. This will also result in cooler temperatures, with areas west of the Divide in the lower 80s and areas east of the Divide in the middle to upper 80s to near 90 degrees. A trough will then drop southward from Canada over MT Thursday into Friday with the associated cold front reaching far northern portions by 00Z Friday. Showers and thunderstorms will then be possible along and behind the front as it progresses southward Thursday night. Models are currently progging the front to quickly sweep through the area and exit into the High Plains by Friday afternoon. Precipitation chances could linger over areas east of the Divide, especially Johnson and Natrona counties, given that the models tend to be too fast with systems this far out in the forecast period. Nevertheless, temperatures will be cooler Friday, especially east of the Divide, about 10 to 15 degrees cooler compared to Thursday (and even 25 to 30 degrees cooler compared to Wednesday!). Dry conditions then return for the weekend, with seasonal temperatures on Saturday. Isolated showers and/or thunderstorms could occur over far southwestern portions Sunday afternoon. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 401 AM MDT Tue Jul 8 2025 VFR conditions expected throughout the entirety of the period for all TAF sites. Winds increase after 17Z-19Z with weak gusts up to 18kts at KBPI/KPNA/KRKS/KCPR with other locations 10kts or less through the afternoon even with the daytime heating and mixing to the surface. An isolated shower or thunderstorm with wind gusts over 35 knots can`t be ruled out this afternoon, mainly in vicinity of KLND and KRIW between 20Z and 00Z Wednesday. The chance is only around 1 out of 6 so not enough confidence to include in TAFs at this time. Winds diminish after 00Z-01Z towards sunset with the limited clouds clearing out. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .FIRE WEATHER... Issued at 137 AM MDT Tue Jul 8 2025 RH values will be critical across much of the area, including zone 140. Even the high elevations will be in the 15 to 20 percent range this afternoon. Afternoon west-northwest winds will generally be under 25 mph, though gusts 25 to 30 mph will occur over the northwestern mountains. Isolated virga showers could occur over zones 282, 283, 287, the southern end of 286 and the northern end of 288 this afternoon. Stronger wind gusts will occur from any shower, with gusts of 55 to 60 mph certainly possible. Widespread elevated fire weather conditions continue Wednesday as temperatures increase and critical RHs spread. Wednesday will be the hottest and driest day, with widespread afternoon RHs 8 to 15 percent. These conditions will even spread into zones 285, 286, 287 and 288. High temperatures will also be in the 90s to around 100 degrees for much of the area. Ahead of the next system, west to southwest winds increase across the area Wednesday afternoon, with gusts 20 to 30 mph. Isolated virga showers will be possible again, with gusts of 55 to 60 mph being the main threat. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...LaVoie AVIATION...Hattings FIRE WEATHER...Wittmann