133 
fxus65 kcys 110903 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
303 am MDT Sat Oct 11 2008 


Short term...today and tonight... 
upper low organizing over southern Nevada early this morning with one 
piece of vorticity having ejected northeast over eastern Idaho. Precipitation 
has diminished over the County Warning Area this morning as some middle level drying 
has occurred behind lead shortwave. This lull has been expected and 
do not see much more in the way of precipitation for the County Warning Area this morning 
into the afternoon thus have shaved probability of precipitation down some. Precipitation will 
begin to increase from west to east by late this afternoon as 
upper low begins to lift northeast and main shot of shortwave 
energy makes its approach to the area. This should bring an area 
of rain and snow across most of the County Warning Area tonight with activity 
tapering off over the western County Warning Area late tonight. Main problem is 
precipitation type and timing of changeovers. Expected temperature 
profile of the atmosphere and prognosticated thickness values favor 
precipitation being mainly liquid over much of the County Warning Area outside of 
the mountains today...then a gradual changeover to snow from west to 
east tonight as middle level temperatures cool with approach of upper 
low. Still appears precipitation will remain primarily rain over most of 
the Panhandle through tonight. Continue to lean toward the cooler 
side of guidance temperatures especially over the eastern Wyoming plains where 
clouds and modest upslope flow will hinder much in the way of 
warming today. 


Based on above reasoning and expectations have made some alterations 
to timing of hilites as worst weather outside of the mountains looks to 
hold off until the evening. 


Long term...Sunday through Friday... 
forecast models continue to show a quick transition to isentropic 
down-Glide across the area from west to east as the upper level 
energy ejects northeast from the area. Have increased 
precipitation chances early Sunday morning in the Nebraska 
Panhandle...but then decreased from inherited forecast as even 
support for orographic snow showers in the Sierra Madre and snowy 
ranges do not appear as likely as earlier forecast. Have lingered 
middle and high cloud cover across southeast Wyoming and the Nebraska 
Panhandle through Monday...as lingering energy in the base of the 
upper trough will be slow to move east of the area. The European 
and NAM are showing the lingering base of the upper trough over 
Colorado even by midday Tuesday...while the GFS is forecasting 
near zonal flow to almost a weak upper short-wave ridge. Then the 
GFS and European show similar upper level flow features...but have 
varying strength on the trough moving along the Canadian border 
Thursday into Friday. The European is much more amplified with the 
trough and thus creates a cold front and moves it through the 
forecast area Thursday or Thursday night. Temperatures through the 
long term will start off around 10 degrees below normal for Sunday 
and Monday...before warming to slightly above normal values 
through the remainder of the week. 


&& 


Aviation... 
widespread MVFR/IFR conditions expected across the area 
today mainly due to low ceilings. More widespread IFR conditions for 
low visibilities along with low ceilings tonight with a period of rain and/or 
snow occurring over most locations. 


&& 


Cys watches/warnings/advisories... 
Wyoming...Winter Storm Warning until 6 am Sunday for wyz062-wyz063-wyz064. 
Winter Storm Warning from 6 PM Saturday to 6 am Sunday for 
wyz059. 
Dense fog advisory until noon Saturday for wyz066. 
Winter Weather Advisory from 6 PM Saturday to 6 am Sunday for 
wyz061-wyz065-wyz066. 
NE...none. 


&& 


$$ 


Short term/aviation...re 
long term...CArpenter