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fxus65 kcys 212246 
afdcys 


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


Short term...tonight through Monday...upper trough moving out of 
Utah and eastern Idaho currently. Models seem to be handling it well 
and progress it across Wyoming tonight to near eastern Wyoming border just 
after 12z Sunday exiting our eastern County Warning Area before 18z. Pacific cold 
front has advanced out of southeast Wyoming now and will pass through Nebraska 
Panhandle next couple hours. Gusty winds that accompanied the 
front earlier have decreased through afternoon. There will be lots 
of clouds over the County Warning Area tonight with some snow showers over the 
mountains accumulating to perhaps an inch or so. A few snow 
showers are also possible klar-kcys per GFS so included a low pop 
there as well tonight. Improvement from west to east behind upper 
trough late tonight then shortwave ridge will prevail over the County Warning Area 
Sunday bringing dry conditions. Next upper trough in the 
progressive upper air pattern will move in Sunday night... with a 
timing not all that unlike the one tonight. Difference is the 
latter upper trough is much stronger with veering upper flow and 
an upper low develops with it to our east. It also is slower to 
move out. Models are getting closer to a convergent solution on 
this latter trough but still show some differences...upper low 
does not really get cranked up until it gets too far east of US. 
GFS has slowed down and European model (ecmwf) is not quite as deep as fast as it 
was on the 12z Friday run. Still...there will be wind and snow for 
most areas with this feature and its associated cold front...with 
a few inches falling in the mountains. An advisory may end up 
being necessary for the south central Wyoming mountains Sunday night 
and Monday morning while a Wind Advisory is likely for the 
Nebraska Panhandle Monday. Both are too early for now. Temperatures will 
be colder both days. 


Long term...Monday night through Saturday...models in good 
agreement earlier in the week...and then show diverging solutions 
late in the week and early next week. GFS...Gem...and European model (ecmwf) show 
mainly northerly flow across the Front Range through Thursday as an 
upper level trough exits east of the region on Tuesday...and a 
backdoor polar front moves into the High Plains on Wednesday. This 
will keep temperatures on the cold side through the middle of next week 
with models hinting at highs in the 30s across most of the area and 
lows in the teens and twenties. Did not go quite that low in the 
forecast with the European model (ecmwf) showing the bulk of the colder air further 
to the east. Do not expect much precipitation as the main jet energy will 
be east of the area and models show little moisture with the front. 
Kept low pop across the area through the week with 20 percent pop across 
the northern ridges of the Nebraska Panhandle and eastern Wyoming. By late in 
the week...00z GFS and GFS ensemble show an upper level ridge 
drifting east over the area resulting in warmer temperatures and clearing 
skies. In contrast...the European model (ecmwf) shows an upper level trough from the 
northern Pacific pushing across the northwest coast on Friday and into 
the Rocky Mountain region for next Saturday...with some snow over 
the area and a continuation of cold temperatures. With poor model 
agreement...limited confidence in the forecast after Thanksgiving 
day. Increased pop towards climatology for Friday night and next Saturday 
and kept temperatures near or slightly below normal normal. 
&& 


Aviation...mainly VFR conditions expected through tonight with 
westerly winds between 15 to 25 kts and gusts up to 35 kts early 
this evening...diminishing to 10 to 15 kts after sunset. There is a 
10 percent chance of MVFR conditions and brief light snow this evening at 
krwl...kcys and klar as a weak cold front pushes across the area 
tonight...otherwise...expect ceilings to remain above 3k feet above ground level 
tonight through tomorrow with any snow mainly confined to the 
mountains. 
&& 


Fire weather...no concerns through Monday. 
&& 


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


&& 


$$ 


Short term...jlh 
long term...tjt 
aviation...tjt