611 
fxus65 kcys 210306 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
906 PM MDT Sat Mar 20 2010 


Update... 
satellite pics depict generally clear skies across the County Warning Area this 
evening. Upstream clouds are expected to dissipate as they move 
into the upper ridge axis. Thus have decreased sky cover some 
overnight. Also dropped temperatures in the Sidney area a couple 
of degrees. Most places will see diurnal cooling overnight with 
the exception of areas where west winds will sustain boundary 
layer mixing...specifically the extreme southeast Wyoming High 
Plains. 


Jtl/Hahn 


&& 


Previous discussion... /issued 210 PM MDT Sat Mar 20 2010/ 


Short term...tonight through Monday... 
warmer and drier weather will be over the County Warning Area through Monday 
morning. Height aloft rise over The Rockies through Sunday with 
the ridge axis over the County Warning Area Sunday afternoon. Temperatures will 
be above normal during that time as 700 mb readings rise to above 
zero Sunday afternoon. Middle and high level clouds will spread into 
the County Warning Area Sunday and Sunday night behind the ridge axis. The main 
concern through Monday morning will be the gusty westerly winds 
along and west of the Laramie range. Winds have gusted as high 
as 35 miles per hour this afternoon in some locations. Winds may diminish 
some this evening before increasing again later tonight. The 
surface pressures will fall over the area through Monday morning 
ahead of an approaching cold front...and the surface pressure 
gradient will tighten. The low level height differences across 
the County Warning Area also increase later tonight and continue through Monday 
morning. The 700 mb winds also increase to between 30 and 40 
knots. For now have increased the wind speeds along and west of 
the Laramie range late tonight through Monday morning...but will 
keep below high wind criteria levels. 


A surface cold front will move east on Monday and models are 
close in depicting its location from kcdr to kcys by 00z Tuesday. 
The surface low pressure trough should persist ahead of the front 
over the far eastern Panhandle at that time. The associated 
upper level storm system will be over Idaho and Utah 00z Tuesday 
with a shortwave trough moving across the County Warning Area. The lapse rates 
decrease Monday afternoon over the County Warning Area with lifted indices 
between 0c and -1c. Will mention thunderstorms in the forecast 
for Monday afternoon with the focus being along the cold front 
and surface low pressure trough. Temperatures will be kept lower 
on Monday by the passage of the cold front and the cloud cover... 
but will still be well above normal. 


Long term...Monday night through Saturday... 


Focus in the long term deals with another potential storm system 
Monday night into Tuesday. Medium range models not in very good 
agreement with this system. GFS and WRF keep an open system with 
highest probability of precipitation initially over northern Wyoming with cold front moving 
south across the state Monday evening/Tuesday morning. The European model (ecmwf) 
has a slower solution with a closed low over eastern Idaho Monday 
night into Tuesday...then tracking into Utah Tuesday afternoon for 
a slower...more prolonged precipitation event. Given the consistency with 
the GFS and WRF...went ahead and followed its solution for this 
forecast. Started increasing probability of precipitation for the area as the front moves 
into western Wyoming late Monday afternoon. Both the WRF and GFS 
showing considerable instability Monday afternoon and evening 
ahead of the front. Granted...models are showing a low level cin 
around 30-50 j/kg Monday afternoon...but this cap should be wiped 
out by the approaching front early Monday evening. So have gone 
ahead and added some isolated thunderstorms to the forecast Monday 
evening. Majority of the precipitation looks to be behind the front after 
midnight into Tuesday morning...which should turn quickly over to 
snow. 


Bulk of precipitation moves south into Colorado Tuesday night into 
Wednesday with ridging returning to the area Thursday. Next system 
approaches the area Thursday night into Friday for increasing 
precipitation chances towards the end of the week. 


Aviation...VFR conditions are expected over the County Warning Area through 
Monday. Cloud bases will lower Monday afternoon with some 
showers and thunderstorms present. Westerly winds will gust as 
high as 35 knots in some areas along and west of the Laramie 
range through 00z. Winds should increase again late tonight in 
that area with gusts as high as 40 knots. Those winds will 
continue through Monday. With westerly winds around 40 knots 
around mountain top level late tonight through Monday...a weak 
mountain wave can be expected to the Lee of the Snowy Range and 
Laramie Peak. 


Fire weather...dry and warmer conditions will be over the County Warning Area 
through Monday morning. Temperatures will be well above normal 
during that time and minimum relative humidity values will be 
between 20 and 30 percent over the lower elevations Sunday 
afternoon. In addition...westerly surface winds will gust as high 
as 45 miles per hour in areas along and west of the Laramie range early this 
evening and then again late tonight through Monday morning. A 
cold front will move across the County Warning Area Monday and Monday evening 
and will produce some showers and thunderstorms along with a 
shift in the surface winds to more northwest. 


&& 


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


&& 


$$ 


Short term/aviation...Weiland 
long term...claycomb