


Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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826 FXUS65 KRIW 070738 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 138 AM MDT Mon Jul 7 2025 .KEY MESSAGES... - Warmer temperatures Monday through Wednesday with an increasing chance for elevated fire weather conditions due to low relative humidity and hot temperatures. - Very hot conditions with widespread 90s and some locations getting close to the triple digit mark Tuesday and Wednesday. The lowest elevations of the Bighorn and Wind River Basins have a 30-50 percent chance of 100 degree highs Wednesday. - A 20-40 percent chance of thunderstorms returns Friday afternoon and evening, especially along and east of the Continental Divide. && .DISCUSSION... Issued at 132 AM MDT Mon Jul 7 2025 Mostly dry conditions, light winds and mostly clear skies will continue today. An upper level ridge will build over the region through the day from a strengthening high center over the Four Corners. Moisture will be confined along the I-25 corridor today, with MLCAPE of 1500-2000 J/kg and a lifted index of minus 4 to minus 6. The tail end of a shortwave passing over the Northern Plains could provide enough lift for a few showers and thunderstorms over Johnson County this afternoon. Locally heavy rain will be the main threat, as precipitable water values will be over 0.75" (which will be near the 90th percentile) in addition to the previously mentioned variables. Small hail could also occur as directional shear will be quite strong (sfc easterly winds and 700mb westerly winds). The mitigating factor here in this is the speeds will be quite weak at 20 kt or so. A weak, shallow back door cold front associated with the trough will push through Natrona County and the Wind River and Bighorn Basins after sunset this evening, turning winds easterly in its wake. The front will stall and wash out by sunrise Tuesday morning. The warming trend will continue Tuesday, with 90 degree temperatures returning for areas east of the Divide as well as across portions of Sweetwater County. Isolated virga showers will be possible,mainly over the central basins through the afternoon. Wind gusts of 55 to 60 mph will be possible from these showers, due to the large dewpoint depressions. This convection does not look likely to repeat itself on Wednesday, as the ridge begins to shift eastward over the Cowboy State leading for the atmosphere to remain capped for most areas. Several locations east of the Divide could reach 100 degrees as a result of these capping inversions, including Greybull, Worland, Thermopolis, Casper and Riverton. The GFS MOS guidance is forecasting 100 degrees at Riverton, Worland and Greybull. The next chance for precipitation looks to occur Thursday or Friday afternoon. A remnant low will move over the Cowboy State Thursday morning and exit over the NE Panhandle late in the afternoon. This low could bring showers over southern portions. A trough will then drop southward from Canada over MT Thursday night into Friday. This could result in showers over northern portions Friday morning and thunderstorms across areas east of the Divide during the afternoon. This trough would lower temperatures 10 to 15 degrees for areas east of the Divide and cause the Four Corners high to retreat further south. Strong northwest winds could hit northern Johnson County, including Buffalo, in the wake of the cold front associated with the trough. No strong wind signatures are evident yet, but gusts of 50 to 60 mph could occur as this would be common with these kinds of fronts. The cooler temperatures will be short-lived however, as high pressure rebuilds over the area and readings return to the middle to upper 80s on Saturday. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1055 PM MDT Sun Jul 6 2025 Terminals to be VFR through 06Z/Tuesday as drier air aloft punches farther east across the forecast area. Several outflow boundaries and weak instability have allowed for lingering convection late Sunday evening, which should end by 08Z/Monday. KCPR would be the most likely terminal to see outflow or a brief sprinkle. Convection that reignites Monday afternoon and early evening will be confined to areas around and east of a KBYG-KCPR line. Also, weak convection occurs south of KRKS where showers and storms move east-northeast off the Uinta Mountains. Otherwise, shower and thunderstorm chances are less than 10 percent. Afternoon westerly wind 10-15kts will be common at terminals west of the Continental Divide until 02Z/Tuesday. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...LaVoie AVIATION...CNJ