Winter Weather Storm expected on the first day of Winter (Updated ~2 am 12/21)

A vigorous winter storm system will dive southward into the Intermountain West today, bringing a change to the weather pattern and a decent amount of snow to the Cowboy State.  Snow has begun this morning across northern portions, already dropping over 4 inches in some places. The snow will continue to spread southward and will intensify this afternoon into tonight. Winds will increase behind a fast moving cold front, which will aid in upslope conditions as well as blowing and drifting snow. Gusts of 20 to 25 mph will mainly occur across central and northeastern portions, however gusts up to 30 mph will be possible near South Pass and the Rattlesnake Range.  These gusts are expected to occur toward midnight.   

The above animation shows the expected surface wind speeds with the 6 hour model snow accumulation underlaid as an image. The arrows at the tip of the wind barbs show the direction to which the wind is blowing. Click here for more information on how to read a wind barb.

The image shows the amount of snow expected to accumulate every six hours, beginning at 12Z Tue (5AM Tuesday Morning). The animation goes through 06Z Fri (11PM Friday Night). The time stamp is located at the bottom right hand side of the image (in UTC or Z time). Click above for a full resolution version of the animation.

The above animation shows the temperatures at 700 MB (about 9500 ft above the surface) with the overall flow overlaid (white contours). Click above for a full resolution version.

Conditions will remain cold in the wake of this system, as the airmass becomes trapped again and high pressure builds back over the area.

Here are preliminary forecast totals across Western and Central Wyoming (5 AM Today - 5 AM Thursday):

Click for a larger image.

Keep an eye on our homepage for the latest forecasts, Watch/Warning Information, and Area Forecast Discussion for more analysis from a forecaster, and please "like" us on Facebook to share pictures and reports with us during the storm. Continue to stay tuned for more detail in future Watches, Warnings, and Advisories on the timing and severity of expected conditions near you. To keep track of current road conditions across Wyoming call 5-1-1 or go to

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