FXUS65 KRIW 200713 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 113 AM MDT Wed May 20 2026 .KEY MESSAGES... - Virga showers will occur this afternoon, developing over the western mountains and moving over the Bighorn, Wind River and Upper Green River Basins. Wind gusts up to 45 mph will be possible with any passing shower. - Precipitation arrives from the northwest late tonight and becomes widespread Thursday. Cooler temperatures by Thursday evening could lead to a period of light snow in upslope- favored areas around Lander and Beaver Rim. - Forecast trends continue to favor widespread high temperatures in the 70s to mid 80s for the three-day Memorial Day holiday weekend. Other than a few late day showers, conditions look dry each day. && .DISCUSSION... Issued at 110 AM MDT Wed May 20 2026 The warming trend continues today, but temperatures will still be below normal for central and southern portions of the CWA. Eastern portions of the Bighorn Basin will have near normal highs near 70F. Virga showers will be more widespread across the CWA this afternoon, as winds aloft back to the west-southwest through the day. Most of the showers will develop over the western mountains and move over the Bighorn, Wind River and Upper Green River Basins through the afternoon. Wind gusts up to 45 mph will be possible with these showers, as dewpoint depressions will range between 30 and 50 degrees. Winds outside of any potential outflow will be light, 20 mph or less. Precipitation chances will become more focused over northwestern portions tonight as the storm drops southward, gradually pushing east and south into the Bighorn Basin, the western valleys and the Upper Green River Basin through the overnight hours. Snow levels will be as high as 9500 ft early in the evening and drop to around 7000 ft by 12Z Thursday. The associated cold front with this incoming storm system will drop southward over the CWA through the overnight hours as well, extending along a Casper-to-Riverton-to Kemmerer line by 12Z Thursday. The front will then slowly push through Natrona and Sweetwater counties through the rest of the morning, with a leeside low developing over northeast portions of WY by 18Z. The aforementioned area of precipitation will continue to move over the CWA through the rest of the day. Model trends have warmed the associated 700mb cold pool that pushes through the Bighorn and Wind River Basins during the afternoon and are now forecasted to be around minus 4C/minus 5C (snow levels as low as 6000 ft). Areas along and north of a Meeteetse-to-Lovell line could still see rain changing over to snow after 18Z. However, precipitation looks to end during the afternoon along a Jackson-to-Cody-to-Lovell line as drier air begins to advect in from the northwest behind the storm. Similar conditions could occur at Lander by 00Z with a greater chance for accumulating snow. There will be an added upslope component, aided by a potential 700mb low moving along the Divide between 00Z and 06Z. This could be enough to dynamically cool the column and lead to snow for the Lander Foothills. Current forecast is for conditions to quickly dry out from west to east through the overnight hours Thursday night, but if the storm slows down precipitation could continue over central and southern portions through 12Z Friday. Initial snowfall amounts of 6 to 8 inches are forecasted over the Absaroka, Wind River and the northern half of the Bighorn Mountains, with up to 4 inches over the Tetons, Gros Ventres and portions of Yellowstone. Temperatures rebound quickly on Friday, with a chance for showers over the far western mountains again in the afternoon as a weak shortwave moves over the area. Afternoon showers and possible thunderstorms will be possible over the holiday weekend as highs reach the middle to upper 80s by Monday. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1042 PM MDT Tue May 19 2026 West of the Divide...KJAC/KRKS/KPNA/KBPI Terminals Northwest flow aloft backs to the west as a shortwave drops south toward the forecast area late Wednesday afternoon. Weak showers develop over the mountains 19Z-21Z/Wednesday and move east into the basins and valleys around KJAC and KBPI. Any impacts would be brief and confidence is not high enough to include PROB30, with KJAC being the most likely terminal. Shortwave energy and deeper moisture reaches northwest Wyoming around KJAC late in the period, so a PROB30 group has been added beginning at 04Z/Thursday. In general, cloud cover increases and begins to slowly lower after 00Z/Thursday. Wednesday afternoon westerly surface wind 10-18kts decreases to 7- 10kts around 02Z/Thursday. Mountain tops occasionally obscured after 00Z/Thursday over northwest Wyoming. East of the Divide...KCPR/KCOD/KRIW/KLND/KWRL Terminals All terminals to be VFR through the forecast period. Weak showers develop over the Absaroka and Wind River Ranges 19Z-21Z/Wednesday and slowly track east into the basins during the afternoon. Impacts are likely to be confined to gusty outflow wind 25-35kts, with convection around KCOD the most likely to produce these gusts. Otherwise, KCPR to see 10-18kt westerly wind during the day with occasional late day westerly wind 9-13kts at KRIW and KLND. The arrival of more robust shortwave energy in northwest Wyoming leads to a better chance of light rain showers at KCOD late in the period. This shortwave will begin to push a cold front accompanied by northerly surface wind through the Bighorn Basin after about 03Z/Thursday. Mountain tops obscured after 00Z/Thursday in the Absaroka Range. Please see the Aviation Weather Center and/or CWSU ZLC and ZDV for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... Freeze Warning until 8 AM MDT this morning for WYZ005-006-011- 016>020. && $$ DISCUSSION...LaVoie AVIATION...CNJ/LaVoie