A major shift in the jet stream and storm track will bring winter conditions to much of the Western States by Christmas Day. Here is a series of 500 mb maps showing the change expected.
Riverton National Weather Service Forecast Office has issued Winter Storm Watches.
URGENT - WINTER WEATHER MESSAGE National Weather Service Riverton WY 302 AM MST Tue Dec 21 2021 Star Valley- Including the cities of Afton, Alpine, Star Valley Ranch, and Thayne 302 AM MST Tue Dec 21 2021 ...WINTER STORM WATCH IN EFFECT FROM THURSDAY MORNING THROUGH FRIDAY MORNING... * WHAT...Heavy snow possible. Total snow accumulations of 6 to 9 inches possible. * WHERE...Star Valley. * WHEN...From 6 AM Thursday through 6 AM Friday. * IMPACTS...Travel could be very difficult as areas of blowing snow could reduce visibility. The hazardous conditions could impact the morning or evening commute. * ADDITIONAL DETAILS...As snow looks to continue into Friday afternoon, winter storm highlights may need to be extended to highlight continuing impacts. PRECAUTIONARY/PREPAREDNESS ACTIONS... If you must travel, keep an extra flashlight, food, and water in your vehicle in case of an emergency. Monitor the latest forecasts for updates on this situation.