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Area forecast discussion 
National Weather Service Cheyenne Wyoming 
219 PM MST Wednesday Nov 19 2008 


Short term...tonight through Friday... 
west northwesterly flow aloft tonight will gradually back Thursday as a 
low amplitude upper ridge moves eastward over Wyoming. The ridge will 
move off to the east and flatten Thursday night as a shortwave upper 
trough moves over Wyoming. The GFS is a bit faster than the NAM with the 
trough. In any event...the shortwave trough will pass over the 
forecast area Friday. A surface backdoor type cold front currently 
pushing through the forecast area will continue moving south tonight 
as a broad dome of Canadian high pressure noses southward over the 
northern High Plains. Surface based upslope flow will deepen and 
moisten tonight with precipitation becoming possible over all but 
the far western portion of the forecast area. Forecast model 
soundings indicate that freezing drizzle is not inconceivable 
tonight east of the mountains due to relatively dry air above a 
layer of supercooled droplets. Because the atmospheric profile will 
be more favorable for freezing drizzle over far eastern portions of 
the forecast area...will mention the possibility of patchy freezing 
drizzle late tonight primarily over the western Panhandle of Nebraska. 
The predominant form of precipitation elsewhere tonight is expected 
to be light snow...with little accumulation expected. Upslope flow 
will continue Thursday but dynamics will weaken...and will taper probability of precipitation 
accordingly Thursday. Thursday will be much colder. Thursday night will be mainly 
dry as a trough of surface low pressure develops over the area. The 
low will combine with surface high pressure to the east to 
strengthen the pressure gradient and produce areas of brisk winds 
late Thursday night. The surface trough will phase eastward over the High 
Plains Friday...with a small chance of precipitation over northern portions of 
the forecast area in closer proximity to the aforementioned upper 
shortwave trough. Temperatures Friday will rebound to approximately normal 
levels. 


Long term...Friday night through Wednesday... 
mainly dry and mild weather expected for the region during this 
period under a progressive upper pattern. Transient upper ridge 
will pass by Saturday bring warmer temperatures. Next upper trough 
passes across the northern rockys and plains and drives Pacific cold 
front across the County Warning Area Saturday night bringing about 10 degrees of 
cooling for Sunday. Upper ridge then moves across during the early 
to middle part of next week allowing for warmer temperatures to return 
before potentially more significant cooling by late in the week. 


&& 


Aviation...middle and low level moisture will increase tonight behind 
a cold front currently moving through the region. VFR conditions 
this evening will lower to MVFR conditions late tonight with areas 
of light snow and patchy freezing drizzle. Mountain obscurations 
will increase tonight into Thursday. 


&& 


Cys watches/warnings/advisories... 
Wyoming...none. 
NE...none. 


&& 


$$