Stormy Start to the Memorial Day Weekend

The advertised pattern change has occurred and the warm, sunny weather of mid May across Star Valley is over for now.  The strong polar jet that moved in off  the Pacific is now located just to our south. 

300 mb analysis Thursday morning 5/24/12

This Thursday morning the strong and cold westerly flow is providing periods of wet snow, heavy at times,across the Valley.  A photo taken from Star Valley Ranch late Thursday morning is visible evidence.

The following series of 500 mb forecast charts shows an intense upper low that develops within the strong jet stream and its path over the  Memorial Day Weekend.

500 mb analysis Thursday morning 5/24/12

 

 

500 mb forecast Friday morning 5/25/12

500 mb forecast Saturday morning 5/26/12

500 mb forecast Sunday morning 5/27/12

With the upper low dropping southeastward into California Friday, the upper flow turns  more southerly across Western Wyoming and Southeast Idaho, which will bring a warmer air mass northward. The snow level will rise above Star Valley by tonight, leading to a warmer day on Friday.  While showers will still be possible Friday, any snow should be confined to the higher elevations.

The 700mb chart from this morning compared to the forecast for Friday evening depicts  warming of the air mass in western Wyoming.

700 mb analysis Thursday morning 5/24/12

700mb forecast Friday evening 5/25/12

Another period of possibly significant precipitation will occur as the upper low moves northeastward across the area later Saturday into Sunday morning.  For the duration of the next 3 days, the model forecasts an inch or more of precipitation from the Star Valley area northward.

Model Forecast precipitation Thursday morning to Sunday morning 5/24-27/2012

The greatest impact from this storm appears to be north of Star Valley where potentially heavy snow fall from one to two feet is possible in the higher mountains such as the Bear Tooth in Southern Montana.  Here is a  statement issued by the Great Falls WFO for Montana to alert weekend travelers.

http://www.wrh.noaa.gov/FXC/wxstory.php?wfo=tfx