Weather

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Area forecast discussion 
National Weather Service Cheyenne Wyoming 
452 PM MDT Monday Oct 6 2008 


Discussion...have went ahead and issued a frost advisory for east 
central Wyoming later tonight and early Tuesday morning. Lows 
should be in the upper 20s and lower 30s as the surface high moves 
over the region. 


&& 


Previous discussion.../issued at 237 PM MDT Monday Oct 6 2008/ 


Short term...tonight through Wednesday... 
upper trough now east of the County Warning Area with northwest upper flow over the region. 
Afternoon instability cloudiness over some of the County Warning Area will dissipate 
early this evening leaving mainly clear skies overnight. Chilly 
temperatures still on track and will maintain mention of frost 
outside of mountain areas tonight but not hoist frost advisory as it is 
already pretty late in the season and some frost has already occured 
over many areas. Warmer temperatures return for Tuesday and 
Wednesday as upper ridge slides across with a zonal flow over the 
region Wednesday. Increasing middle-level flow will lead to some 
breeziness over mainly the western County Warning Area Tuesday and Wednesday afternoons 
otherwise quiet weather will continue. 


Long term...Wednesday night through Monday... 
fast zonal flow aloft will back to southwesterly Wednesday night. Weak 
shortwave energy will move through the flow Thursday then a major upper 
trough will develop over the western U.S. Friday as jet energy digs 
southeastward down the backside of the developing trough. Models 
squeeze off a cutoff low...but differ on the details. European model (ecmwf) is 
deeper and slower than the GFS with the cutoff Saturday...then the 
European model (ecmwf) quickly whisks the cutoff northeastward to eastern Montana by late 
Sunday afternoon while the GFS keeps the cutoff to our south and 
moves it to northeast Colorado/southwest Nebraska by late Sun afternoon. These 
scenarios are fairly significantly different...and much uncertainty 
exists regarding the weather next weekend. In any event...it appears 
as though cyclonic upper flow will remain over the forecast area 
next Monday. Closer to the ground...Thursday will be cooler with increasing 
probability of precipitation from the north and west as moist surface upslope flow interacts 
with shortwave energy to trigger some showers. Low level upslope and 
cold air advection will both continue Friday into Sat as surface high 
pressure noses southward down the High Plains. Sat looks to be the 
chilliest day this Young autumn season. The nights will be cold 
enough to allow for some changeover from liquid precipitation to wet 
snow showers in many areas each night from Wednesday night through Sat 
night. Sun will be somewhat milder with lingering moisture as 
precipitation remains possible. Monday will be dry with temperatures 
continuing to rebound as the best moisture and lifting dynamics move 
off to the east. 


&& 


Aviation...VFR conditions expected through Wednesday. 


&& 


Cys watches/warnings/advisories... 
Wyoming...frost advisory late tonight and early Tuesday morning for east 
central Wyoming. Zones 59 and 60. 
NE...none. 


&& 


$$ 


Weiland