967 
fxus65 kcys 211905 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
1205 PM MST Sat Nov 21 2009 


Update...have allowed hi wind warning for Karl to expire at 19z as 
winds there have decreased quite a bit since 1815z. Jlh 


&& 


Previous discussion... /issued 926 am MST Sat Nov 21 2009/ 


Update...have issued local High Wind Warning for Arlington area of 
south central Wyoming until 19z. Sustained speeds of 40 miles per hour have been 
occurring there since 1430z with one gust to 60 miles per hour around then and 
more to 65 miles per hour currently. Winds should slowly decrease behind a 
cold front by middle afternoon. Jlh 


Previous discussion... /issued 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 the 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 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/aviation...Weiland 
long term...kmd 

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