FXUS65 KRIW 180850 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 250 AM MDT Mon May 18 2026 .KEY MESSAGES... - Snow will continue to fall across the Wind River Basin, Natrona County and Sweetwater County this morning. Greatest travel impacts expected around Lander, Casper, South Pass, and over Interstate 80. Gusty winds and snow will bring reduced visibilities and possibly icy surfaces with colder temperatures moving in. Wind gusts up to 70 mph will be possible over South Pass and over Interstate 80. - Warming trend and mainly dry conditions for most of the CWA Tuesday and Wednesday with another Canadian cold front impacting the area on Thursday. This storm does not look to be as cold as the current storm. - Medium confidence for above normal temperatures returning for at least the first 2/3 of the holiday weekend. && .DISCUSSION... Issued at 240 AM MDT Mon May 18 2026 Rain changed over to snow in the Wind River Basin and across Sweetwater County just a few hours ago after 11pm Sunday night. Much of Natrona County is around 37F degrees as of 08Z (2am), with precipitation still falling as rain. The forecast remains on track this morning, with the threat of snow and wind impacting areas from South Pass southward into Sweetwater County. The 700mb low from this storm system will be passing close to the CO/WY border this morning, resulting in a tight temperature and pressure gradient. 700mb northeast winds of 50-60kt will occur from the Green Mountains/Rattlesnake Range into Sweetwater County. This will result in wind gusts of 60 to 70 mph occurring this morning over locations like South Pass down to the Rock Springs/Green River area. Windy conditions (wind gusts up to 35 mph) will be widespread across the CWA this morning as the storm system moves over CO this morning. Snowfall amounts of 2 to 6 inches is still expected across portions of Natrona County, the Lander Foothills and the eastern half of Sweetwater County. Travel conditions could be difficult this morning due to the blowing snow and icy roads. Impacts from snow accumulations on roads is likely to only last through 15Z/16Z (9am or 10am) as it will be more difficult for the snow to stick due to the high sun angle. These impacts will begin to decrease through the morning, with areas like Lander and Casper improving first as snow begins to end toward midday. Impacts along I-80 will last the longest due to the proximity of the 700mb low, but is expected to wane between 18Z and 21Z as snowfall ends. Winds will be decreasing across the area after 18Z as well, with the stronger winds of 35 to 40 mph continuing from South Pass southward into Sweetwater County and decreasing through the afternoon. Needless to say, temperatures will be anywhere from 5 to 25 degrees colder today and about 15 to 30 degrees below normal. Winds will continue to decrease this evening, as the storm system quickly exits over the Central Plains and light winds (10kt or less) expected for most areas by 06Z Tuesday. Fog development could occur as late as sunrise Tuesday morning as clouds are expected to remain in place across central and southern portions of the CWA through much of the night tonight. Dry and warming conditions are expected Tuesday and Wednesday, with another Canadian storm system impacting the area on Thursday. This system doesn't look to be as cold as today's storm and snow levels staying around 7000ft at this time. Model guidance remain split at this time, but confidence is medium for a mainly dry holiday weekend for at least 2 of the 3 days. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1000 PM MDT Sun May 17 2026 Impactful winter weather conditions will continue at Wyoming airports overnight into Monday. Locations that are currently seeing rain will likely switch over to snow after 18/0600Z, and widespread IFR conditions are forecast at many locations in central and southern Wyoming. KCOD looks to remain north of the precipitation, but showers will impact the nearby terrain. Mountain obscurations will be ubiquitous over the next 18 hours. KCPR and KLND are worth mentioning specifically for snowfall, as these locations will see snow continue into Monday evening due to favorable upslope flow. Elsewhere, snow should generally taper off during the afternoon hours Monday. Expect gusty north to northeast winds with this system, gusting in to the 20 to 30kt range for most locations. KRKS will be windiest given its position close to the storm center, so gusts will likely be higher, in the 40 to 50kt range overnight. KRKS also has a chance (40%) of morning fog on Tuesday. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 6 PM MDT this evening for WYZ002- 003-005-007>011-014-016-017-026>029. Winter Storm Warning until 6 PM MDT this evening for WYZ015- 018>020-022-030. && $$ DISCUSSION...LaVoie AVIATION...VandenBoogart