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afdcys 


Area forecast discussion...updated 
National Weather Service Cheyenne Wyoming 
846 PM MST Friday Nov 20 2009 


Update...tonight... 
breezy conditions have developed as expected in the Laramie valley 
and this is expected to keep overnight lows in the lower to middle 
20s...much warmer than the past few nights when the very cold air 
has been trapped in the valley. 


Elsewhere...the forecast is on track with dry conditions expected 
overnight. Southwest winds will continue to become breezy across 
the rest of the southeast Wyoming portion of the area as the Lee 
side trough continues to deepen. Southeast winds will continue to 
evolve in the Nebraska Panhandle east of the trough axis 
overnight. Although winds at 700mb are forecast to increase to 
around 50 knots...High Wind Warning criteria is not expected to be 
met as the presence of the cyclonic jet stream to the west should 
provide enough lift and decreased capping to keep strongest winds 
aloft and not force them down to the surface in favored gap wind 
areas like Arlington and Bordeaux. 


&& 


Long term...Sunday night through Friday... 
only system to deal with will be early in this time frame and it 
may pack quite a punch. Models are all over the place with this 
system with GFS fastest and weaker while European model (ecmwf) is slower while 
being the strongest. Canadian is fairly close to the European model (ecmwf) but 
not as slow or quite as strong while NAM is somewhere between the 
GFS and Canadian. At 12z Monday...European model (ecmwf) has upper low developing 
over west central Wyoming vs. Central Wyoming for the Canadian and northestern Montana 
for GFS. NAM has a double low structure over southeast Montana and central Wyoming. 
By 00z Tuesday...both European model (ecmwf) and Canadian have a wrapped up low over 
northwest Kansas with NAM leaning that way while GFS much different showing 
this over eastern South Dakota. Model differences really come down to whether 
the upper trough digs south-southeast to the west of the Continental Divide like 
European model (ecmwf) and Canadian...or east of the mountains like GFS and NAM. HPC 
consensus is the European model (ecmwf)/Canadian and our previous forecast had 
trended things this way although there will be more weather Monday 
and Monday night especially over southeast quarter of County Warning Area. For now...have 
bumped up probability of precipitation and winds and lowered temperatures Monday and Monday night 
especially along and southeast of kcys-kaia line. There could end up being 
a several hour snow event that includes southern Nebraska Panhandle 
with southeast corner Wyoming at the northwest edge. Improving weather over our County Warning Area Tuesday 
behind the deep plains low as upper ridging builds in. GFS shows a 
weak clipper system moving into northern County Warning Area Tuesday night while 
European model (ecmwf) keeps this further to the northeast...kept a low pop across 
northern County Warning Area. Both Wednesday and Turkey day will be under strong upper 
ridging for dry and warmer conditions. These will continue Friday 
although next upper trough may start affecting northwest part of County Warning Area 
late. 


&& 


Aviation... 
VFR conditions will prevail through Saturday. Increased upward 
motion along the higher terrain with the frontal passage Saturday 
afternoon will lower cloud cover slightly and create isolated 
instances of mountain obscuration with mountain showers. 


&& 


Fire weather... 
no fire weather concerns at this time. 


&& 


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


&& 


$$ 


Short term/aviation/fire weather...CArpenter 
long term...jlh