A Dramatic Warm Up has occurred in Star Valley over the weekend.  The temperature graph from the Afton airport best depicts the more than 60 degrees rise that occurred from Saturday morning to Sunday morning.

Temperature at Afton Airport January 7-8 2017

This change of airmass is the result of a very moist storm system from the Pacific 

moving inland replacing the bitter arctic airmass. The water vapor imagery from

Sunday evening vividly shows this underway as the moisture from the subtropical 

Pacific surges inland toward Wyoming.

Water Vapor Imagery Sunday Evening January 8 2017

Western Wyoming and Star Valley will experience a direct impact from this and 

additional systems this coming week, with large amounts of snowfall in the mountains

on the order of several feet and potentially 1-2 feet across parts of Star Valley.

It is such a warm air mass now that some of the precipitation may occur as rain in the

valley tonight and Monday, reducing somewhat the snowfall totals but raising the

concern for increased slickness of the roads, particularly Monday morning.

The Riverton Forecast Office has issued the following Winter Storm Warning for Star 

Valley which includes much of Western Wyoming and adjacent portions of Eastern 

Idaho.

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE RIVERTON WY
208 PM MST SUN JAN 8 2017

...MAJOR LONG DURATION WINTER STORM TO IMPACT THE WEST THROUGH
WEDNESDAY NIGHT...

.SEVERAL WEATHER SYSTEMS WILL IMPACT THE WEST THROUGH WEDNESDAY
NIGHT BRINGING MULTIPLE PERIODS OF MODERATE TO HEAVY SNOW AND
WIND. THE MOST LIKELY TIMES FOR THE HEAVIEST SNOW AT THIS TIME
APPEAR TO BE TONIGHT THROUGH MONDAY MORNING...TUESDAY MORNING AND
AGAIN LATE TUESDAY EVENING THROUGH WEDNESDAY NIGHT.


STAR VALLEY-
INCLUDING THE CITIES OF...AFTON...ALPINE...STAR VALLEY RANCH...
THAYNE
208 PM MST SUN JAN 8 2017

...WINTER STORM WARNING REMAINS IN EFFECT UNTIL 5 AM MST
THURSDAY...

* TIMING...SNOW WILL INCREASE QUICKLY LATE THIS AFTERNOON WITH
  PERIODS OF HEAVY SNOW EXPECTED TONIGHT THROUGH AT LEAST MONDAY
  MORNING. ANOTHER BOUT OF HEAVY SNOW IS EXPECTED TUESDAY MORNING
  AND AGAIN LATE TUESDAY NIGHT THROUGH WEDNESDAY NIGHT LIGHTER
  SNOW BETWEEN THESE TIMES.. .THERE COULD BE A PERIOD OF RAIN OR
RAIN AND SNOW MIXTURE INTO EARLY MONDAY... ESPECIALLY IN THE
LOWEST SPOTS OF THE STAR VALLEY BEFORE COLDER AIR RETURNS
* SNOW TOTALS...1 TO 2 FEET BY LATE WEDNESDAY NIGHT WITH THE

  HEAVIER AMOUNTS TOWARDS THE NORTH END OF THE VALLEY.



* WIND AND VISIBILITY...SOUTHWEST WIND INCREASING TO 15 TO 25

  MPH WITH GUSTS TO 35 MPH IN OPEN AREAS. VISIBILITIES UNDER ONE

  QUARTER MILE AT TIMES IN SNOW AND BLOWING SNOW.
* MAIN IMPACT...ROADS AND HIGHWAYS WILL BECOME SLICK AND SNOW

  PACKED WITH SHARPLY REDUCED VISIBILITY.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW... AND

OR BLOWING SNOW ARE EXPECTED OR OCCURRING. THIS COULD MAKE TRAVEL

VERY HAZARDOUS OR IMPOSSIBLE. IF YOU MUST TRAVEL KEEP SOME FOOD...

WATER... AND AN EXTRA FLASHLIGHT IN YOUR VEHICLE IN CASE OF AN

EMERGENCY. CHECK THE LATEST ROAD CONDITIONS AT WYOROAD.INFO OR BY

DIALING 5 1 1.