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.