FXUS65 KRIW 251135 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 535 AM MDT Sat Oct 25 2025 .KEY MESSAGES... - Increasing clouds today, with high temperatures around 10 degrees above normal. - Gusty southwest winds develop today ahead of the next winter system. Chances are likely (above 75%) for gusts of 50 mph for the Absarokas, and from South Pass to Casper today and Sunday. - Next winter storm arrives starting tonight for the western mountains. Treacherous driving conditions expected for western Passes and entrances to Yellowstone National Park. Winter Storm Warnings have been posted starting tonight. && .DISCUSSION... Issued at 138 AM MDT Sat Oct 25 2025 Pleasant weather in the autumn always seems to be a harbinger of more treacherous weather looming, and this weekend is no exception. Today will see the last of the unseasonably warm weather across western and central Wyoming, with another round of highs in the 60s for most lower elevations. The next incoming weather system will ramp up winds considerably today. Southwest winds at H7 reaching 60 to 70kts will mix down starting this afternoon, focusing initially across the far NW zones. Likely not enough mixing downward to warrant a High Wind Warning at this juncture, but winds will be racing through the valleys in the Park and the Absarokas. As the trough shifts closer this evening, winds will further increase for central Wyoming, bringing gusts above 30 for the rest of western and central WY, with frequent gusts reaching 50 from South Pass to Casper. This leads us to the next winter event as the large-scale trough off the PacNW Coast races east across the Northern Rockies. As the trough moves east, the western mountains are in a favorable placement to get a feed of Pacific moisture lifting along the western slopes. The orographic lifting will wring out a decent amount of moisture as snowfall, especially for the Tetons and Gros Ventres, and into the greater Yellowstone. The period when moisture feeds into the region has increased slightly, resulting in a slight uptick in forecast accum. With an increase in probabilities of 12 inches of snow for Teton and Togwotee Passes (>60%), and a significant amount of snowfall impacting the southern and eastern entrances for YNP (>50% chance 10" for the southern entrance and Sylvan Pass), have upgraded to Winter Storm Warnings tonight through around sunset Monday. Not to be left out, but the Salts/Wyomings, Winds, and the Bighorn Range will also be receiving snowfall with this system, but amounts are remaining lower due to less impacts from moisture getting to these regions. Most lower elevations will remain above freezing for this events, so precip remains liquid except for a short period Sunday night, where a dusting of snow may fall. Once this system moves east, it stalls for a couple days, with H5 ridging buckling behind it across the Rockies, bringing back tranquil period for a large part of next week. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 528 AM MDT Sat Oct 25 2025 Sky cover will gradually increase through the day, with most sites only seeing high cirrus through tonight. Winds will be gusty today, especially for KCPR with gusts to 35kts this afternoon. The next storm system moves into the west tonight. Rain showers will begin to increase at KJAC this evening, which will gradually shift to a rain/snow mix overnight, with cigs falling to 2500. Lower cigs and vis may occur briefly once snow starts as winds will still be gusty. Some shower activity may also reach KBPI/KPNA, but most will not arrive until after 12Z/26. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 11 PM this evening to 6 PM MDT Monday for WYZ001-012. && $$ DISCUSSION...Straub AVIATION...Straub