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fxus65 kcys 212043 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
243 PM MDT Thursday Aug 21 2008 


Short term...tonight through Saturday. 
The main concern with this forecast package will continue to be fire 
weather...as red flag warning is already verifying across the 
western portion of the forecast area. These conditions are resulting 
from pre-frontal gusty southwest winds and very dry relative 
humidities. A cold front will move south across the area beginning 
shortly after midnight and through the area east of the Laramie 
range by around sunrise. Winds in the western zones will increase 
again from the southwest Friday afternoon with relative humidities 
then again approaching critical fire conditions...but to avoid 
confusion will keep just the current red flag warning in place and 
allow the overnight shift to take another look at the latest model 
run to make any red flag highlight decisions for Friday afternoon. 
Believe that the northern portion of Carbon County is the only area 
of concern...and even there conditions should only be marginal for a 
fire weather highlight. Upslope low level winds will gradually 
develop late Friday and the cold front will then move west across 
the rest of the area. As the upslope flow develops...will keep a 
slight chance for thunderstorms in the forecast. Will also keep a 
slight chance across Cheyenne County overnight and early Saturday as 
some weak isentropic lift persists. Middle-level and boundary layer 
moisture continue to increase over the higher terrain and east of 
the Laramie range Saturday afternoon...and will expand the slight 
chances for precipitation across the southeast portion of the area. 


Long term...Saturday night through Thursday. 
Weak upslope south-southeast flow at surface will continue over roughly the 
southeast half of County Warning Area Sat night and Sunday. This will keep enough 
moisture/instability for some thunderstorms most of which will occur Sat 
evening and then Sunday afternoon/evening. A few thunderstorms will 
persist into the nighttime hours though in parts of the Nebraska 
Panhandle. Upper ridging builds in Monday for dry and warmer 
weather...and these conditions should persist into Tuesday ahead of 
next system sweeping across the northern rockies and northern 
plains states. This latter system pushes a decent cold front 
through the County Warning Area Tuesday evening. Upper dynamics will cause a few 
showers over the northern County Warning Area Tuesday night and Wednesday 
morning...otherwise not much weather expected except for cooler temperatures. 
Upper heights will start rising again on Thursday so temperatures will 
bounce back a few degrees with dry conditions. 


&& 


Aviation... 
VFR conditions are expected to prevail this evening and overnight. 
Breezy winds are expected to continue through the evening ahead of a 
cold frontal passage that will begin to move south across the area 
overnight. The areas near a line from kdgw to kcdr will observe the 
wind shift shortly after midnight...with the front expected to be 
through the rest of the area by sunrise. 


&& 


Fire weather... 
will continue to keep the red flag warning posted for the Wyoming 
fire zones 291 through 294 through 800 PM MDT...as strong winds and 
relative humidities will continue to create potential for explosive 
fire growth through the early evening hours. Temperatures will then 
begin to cool with relative humidities recovering to 40-50 percent 
across the west...and generally to 60-70 percent over the higher 
terrain and east of the Laramie range. A cold front will shift the 
winds to northwest and continue gusty conditions. The front will 
enter the district shortly after midnight and move south along and 
east of the Laramie range overnight. The front will then move west 
across the rest of the district Friday evening...but before it does 
southwest winds will increase again across northern Carbon 
County...Wyoming zone 293...Friday afternoon. Minimum relative 
humidities will drop into the upper teens in this area with wind 
gusts expected to exceed 25 miles per hour during the afternoon. 
Elsewhere...minimum relative humidities following the cold frontal 
passage will be slightly higher around 20-35 percent with developing 
lighter upslope winds. 


&& 


Cys watches/warnings/advisories... 
Wyoming...red flag warning until 8 PM Thursday for Wyoming fire weather 
zones 291...292...293 and 294. 
NE...none. 


&& 


$$ 


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