807 
fxus65 kcys 211000 aaa 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
300 am MST Sat Nov 21 2009 


Short term...today through Sunday night 
an active period will be in store for the County Warning Area through 12z Monday. 
A shortwave trough currently over the Pacific northwest will move 
east and across the County Warning Area through 18z Sunday. Models have been 
trending a bit slower with the feature the past few runs but are 
now fairly close with the axis over far eastern Wyoming at 12z 
Sunday. The associated Pacific cold front was located from 
western Montana to Idaho early this morning with 2 to 3 mb three 
hourly surface pressure rises behind the front. The front will 
move across this afternoon and early evening. Considerable middle 
and high clouds will be over the County Warning Area today and tonight prior to 
the passage of the shortwave trough. It will also be windy over 
and near the mountains today with the surface low pressure trough 
over far eastern Wyoming. Wind gusts since 06z have been as high 
as 52 miles per hour at kcpr...Karl and krwl. The wind speeds may be the 
highest through middle morning with the temperature inversion present 
and based around 750 mb. Temperatures are currently fairly mild 
in many locations and will help to produce another day with above 
normal temperatures over the eastern part of the County Warning Area ahead of the 
front. There is currently bands of precipitation on the kmtx and 
ksfx radars associated with the baroclinic cloud band now over 
eastern Idaho and northern Utah. The main threat of light snow 
will be over and near the Snowy Range tonight with the passage of 
the shortwave trough. Otherwise expect most of the County Warning Area to remain 
dry. Models differ on the timing and amplitude of the next 
shortwave trough. The feature will deepen over The Rockies Sunday 
night with the associated surface cold front moving across the County Warning Area 
Sunday night. The 00z European model (ecmwf) continues to be slower than most of 
the other models with the shortwave trough but has trended faster 
and with less amplitude than its 12z run. The 00z European model (ecmwf) is favored 
by HPC and so will use that model again for this forecast... 
especially Sunday night. The left exit region of the 300 mb jet 
will affect mainly the south part of the County Warning Area Sunday night and 
moisture will increase. For now will continue the trend of 
increasing probability of precipitation and snow amounts over the County Warning Area for Sunday night. 
Two to five inches of new snow are possible in the Snowy Range 
Sunday night...with an inch or less over most of the rest of the 
south part of the County Warning Area. 


Long term...Monday through Friday 
leaned towards the 00z European model (ecmwf) as it seems to be handling the split 
flow better than the GFS...gems or UKMET. The upper trough will 
move across the County Warning Area on Monday...with the axis moving east of the 
forecast area by evening. An upper low will form over the Central 
Plains Monday night. Cold temperatures can be expected across the area 
Monday with brisk winds in the morning. Some light snow will fall 
across the area...with the best chances in the mountains...but 
lowered probability of precipitation due to best dynamics shifting east as the trough axis 
moves fairly quick across the County Warning Area during the day. An inch or two 
additional snow will fall in the mountains...with less than an inch 
at the lower elevations. On Tuesday...northwest flow will set up aloft as an 
upper ridge build over the western U.S. Dry conditions will persist 
from Tuesday through Friday. Temperatures will moderate a few degrees 
on Tuesday under partly cloudy skies. For Wednesday...mild conditions 
will occur and then very mild for Thursday and Friday with downslope winds 
and sunny skies. The northwest upper flow will flatten out Friday as an upper 
trough moves inland from the West Coast. A cold front will move 
across the County Warning Area late Friday night/early Sat morning. High temperatures 
will be from 5 to 8 degrees below normal Monday...around normal Tuesday 
and Wednesday...and 5 to 8 degrees above normal for Thanksgiving day and 
the Friday Holiday shopping day. 


&& 


Aviation... 
VFR conditions will continue over the County Warning Area today. Cloud bases will 
lower tonight but should still remain VFR. The Snowy Range will be 
obscured tonight. West winds will gust as high as 50 miles per hour through 
middle morning over and near the mountains. Those winds will produce 
turbulent conditions at airports such as krwl...klar...kdgw...kean 
and kcys. Clouds will once again lower Sunday night over the County Warning Area 
with at least periods of MVFR ceilings and visibilities in snow 
over the south part of the County Warning Area. The Snowy Range will be obscured 
again Sunday night. Icing will be a concern with cooler 
temperatures and increased moisture. 


&& 


Fire weather... 
westerly surface winds will gust as high as 50 miles per hour over and near the 
mountains through middle morning. Lower wind speeds are then expected 
through Sunday. Minimum relative humidities will be be between 23 
and 30 percent this afternoon and again Sunday afternoon. Even 
with the gusty winds...fire weather concerns will be minimal for 
this weekend. 


&& 


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


&& 


$$ 


Short term...Weiland 
long term...kmd