387 FXUS65 KRIW 062348 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 548 PM MDT Mon Sep 6 2021 .SHORT TERM...(This Afternoon through Tuesday Night) Issued at 220 PM MDT Mon Sep 6 2021 Gusty northwest wind has already surfaced in the Wind River Basin with other locations also ramping up between 1pm and 2pm Monday. Dew points generally between 15F and 25F have led to relative humidity in the single digits given the above normal temperatures. The increased wind is the result of the tail end of a shortwave sweeping east along the Canadian/Northern Plains border. This feature will brush the northern zones with high clouds into the early evening. Wind speeds will decrease between 6pm and 8pm Monday as the atmosphere decouples and the shortwave progresses farther east. At the same time, a weak cold front slides south into the Bighorn Basin and Johnson County accompanied by northerly wind 10 to 20 mph. With better humidity recovery behind the front and decreasing wind elsewhere, the 8pm red flag warning expiration time looks on track. Smoke will move in from the west tonight, otherwise the sky will be clear. This allows for another night of good radiational cooling across the western valleys. Made a few adjustments to overnight lows and relative humidity based on trends over the past few nights and Monday daytime highs. A smoky and relatively cloudless sky greets the day Tuesday. A building ridge of high pressure in the Great Basin with the axis to our west will leave Wyoming in northwest flow aloft. This may somewhat hinder additional smoke filtering into the region by afternoon. Temperatures will be cooler east of the Continental Divide following the passage of the cold front overnight. Daytime highs will be more seasonal in this region. West of the Divide, 700mb temperatures climb to around +15C, so highs in the 80s will be 5F to 10F above normal. Only wind of consequence will be late afternoon west-northwest wind 10 to 15 mph in the southwest basins. Other than a few high clouds, little change anticipated Tuesday night. Again, tweaked western valley temperatures and humidity to account for the nocturnal cooling within a persistent dry airmass. .LONG TERM...(Wednesday through Monday) Issued at 220 PM MDT Mon Sep 6 2021 High pressure remains the dominant feature for the long term with warm and dry conditions. Temperatures will continue to climb through Thursday under a strong ridge. Record breaking highs are looking possible Thursday, but only by a degree or two. It will be worth watching. The ridge will move eastward from Friday onward, although models continue to slow down that movement. Trough to the west will push in showers on Friday, mainly confined along western areas. Gusty winds Friday with the shifting of the pattern, but it will also start a cool down and a little relief from the above normal temperatures. The weekend is looking to have showers and cooler temperatures, with afternoon gustiness. The ridge is still looking to hold in strong, so it will be a challenge timing in any kind of precipitation action next weekend. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 541 PM MDT Mon Sep 6 2021 Gusty west-northwest winds will quickly diminish between 07/0000z and 07/0200z this evening. In the Bighorn Basin, a weak front will slide south from Montana through basins east of the Continental Divide between sunset and 07/0600z. Brief north winds of 10 to 15 kt are possible in the vicinity of this front, but it quickly loses steam after midnight. Light and variable winds prevail from the early morning hours through noon Tuesday. Light northwest winds around 10 kt are expected Tuesday afternoon west of the Divide. && .FIRE WEATHER... Issued at 220 PM MDT Mon Sep 6 2021 Red flag warnings continue until 8 PM Monday with gusty west- northwest wind to decrease between 6 and 8 PM across the lower elevations. Zone 286 could see the wind linger a bit longer. A weak cold front dropping south through the Cody Dispatch and north half of the Casper Dispatch areas Monday evening will bring better relative humidity recovery tonight. Expect a 2 to 4 hour period of gusty north wind 10 to 20 mph to follow passage of this front. West of the Continental Divide, a dry airmass remains tonight under a clear sky. Radiational cooling enables temperatures in the valleys to cool again into the 30s allowing for good humidity recovery tonight for the western valleys. However, plateaus and mountains again see only poor to fair recovery tonight. Most areas, except those generally above timberline, will see winds decrease substantially by sunrise Tuesday. A ridge of high pressure builds over the Great Basin Tuesday and gradually slides east to Wyoming by Thursday. This favors generally light or seasonal wind speeds all three days. A mostly clear sky leads to abundant sunshine and a warming trend Tuesday through Thursday. Temperatures aloft indicate the possibility for near- record daytime highs Thursday. The dry airmass persists with humidity remaining low in the foothill thermals belts and mountains. As the ridge continues slow eastward progression, the upper flow will gradually switch to a more southwest direction. This favors increasing southwest to west wind Friday. A cold front may drop temperatures across the far west Friday, but eastern areas may stay warm with this gusty wind. This scenario will be watched for potential elevated to critical fire weather conditions as the week wears on, particularly within the Casper Dispatch Area. The southwest flow enables moisture to return to the far west and north Friday with a slight chance of showers and isolated thunderstorms possible. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 8 PM MDT this evening for WYZ276>281-283- 285>287-289-300. && $$ SHORT TERM...CNJ LONG TERM...Swanson AVIATION...VandenBoogart FIRE WEATHER...CNJ