FXUS65 KRIW 200507 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1107 PM MDT Tue May 19 2026 .KEY MESSAGES... - A clear sky allows low temperatures Tuesday night to fall into the 20s for many lower elevation locations. While it will be warmer Wednesday, high temperatures remain below normal. - Precipitation arrives from the northwest late Wednesday night 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. && .UPDATE... Issued at 1234 PM MDT Tue May 19 2026 Snow from yesterday is clear on satellite today, with a large portion of central and southern areas white. Melting will occur through the next couple days as daytime highs slowly increase. However, temperatures do remain on the cool side the next few days. As a result, Freeze Warnings are once again in effect for portions of the area that have seen an early start to the growing season. Lows tonight should be in the upper-20s to lower-30s east of the Divide, where the warnings currently are. && .DISCUSSION... Issued at 145 AM MDT Tue May 19 2026 Areas of clouds still linger over central and southern portions of the CWA this morning, as expected. Low clouds have developed in the Upper Green River Basin, in the wake of the residual snow that fell through Monday evening. Low clouds/fog is also expected to develop near Pathfinder Reservoir in southern Natrona County as well as far eastern Sweetwater County near Wamsutter and Creston Junction. These clouds are expected to last through mid-morning. Travelers on I-80 and US-189/191 should exercise caution due to the reduced visibility. Otherwise, clouds will continue to scatter out through the rest of the morning with partly cloudy skies by 18Z. There is a 20-30% chance for fog/low clouds to develop in the Wind River Basin and areas near Casper. Cumulus clouds will begin to develop over the western mountains after 18Z, with isolated virga showers possible over northern portions of Yellowstone NP, the Cody Foothills, Hoback Junction and Lander/Fort Washakie. Temperatures will be about 10 to 20 degrees below normal today, with sub-freezing temperatures expected again tonight for most areas except northern portions of the Bighorn Basin. The warming trend continues Wednesday, but temperatures stay below normal for central and southern portions of the CWA. Conditions will be dry for most areas, with showers possible over far northern portions irt the next storm system approaching the Cowboy State from the north. Precipitation chances will be confined to northwestern portions Wednesday night, with snow levels between 7000 and 8000 ft, as the storm drops southward. The associated cold front will drop southward over the CWA through the overnight hours, extending from Buffalo to Kemmerer by sunrise Thursday morning. The front will then slowly push through Natrona and Sweetwater counties through the rest of the day. Most of the precipitation with this storm will occur along and behind of the front, being widespread across the CWA through the day Thursday. Rain could change over to snow along and north of a Meeteetse-to-Lovell line after 15Z, as the cold core from the storm pushes into the Bighorn Basin. The challenge will be if snowfall rates will be heavy enough to overcome the high May sun angle. Otherwise, any snow is likely to stay in grassy areas through the day. There could be a similar change over later in the afternoon at Lander. Both of these locations (mainly Cody and Lander) will have a good upslope component with north- northeast winds. There could be a 3 to 5 hour window for snow accumulation between 23Z and 04Z (5pm to 10pm), as the sun begins to wane in the evening. A leeside low will develop over the Black Hills around this time, generating a line of showers and thunderstorms over western portions of SD and NE. Drier air will quickly push in over western portions of the CWA as the storm moves over the aforementioned areas through the rest of the night into Friday morning. Precipitation will quickly end from west to east after 03Z as a result of the storm becoming better organized over SD/NE. However, precipitation looks to linger over Johnson and Natrona counties through the rest of the night. Rain or a rain/snow mix is likely at this time, with snow levels as low as 6000 ft. Initial snowfall amounts around 6 inches are forecasted over the Absaroka and Wind River Mountains and 6 to 10 inches over the northern half of the Bighorns. Temperatures rebound more quickly on Friday, staying at or slightly below normal as the storm quickly exits over the Plains. A pleasant holiday weekend is shaping up, with highs in the 70s and 80s by Memorial Day. && .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 Wednesday for WYZ005-006-011- 016>020. && $$ UPDATE...Wittmann DISCUSSION...LaVoie AVIATION...CNJ/LaVoie