765 
fxus65 kcys 231602 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
902 am MST Monday Nov 23 2009 


Update...current radar loop shows scattered snow showers...mainly 
along and south of i80 this morning...starting to diminish to 
isolated snow showers or flurries as a cold front pushes southeast 
of the region. Snow accumulations have been up to 1 inch so far this 
morning with 4 to 6 inches reported in the mountains. Forecast 
looks on track...conditions expected to improve by this afternoon 
with colder than normal temperatures through tonight. 
&& 


Previous discussion... /issued 330 am MST Monday Nov 23 2009/ 


Short term...today through Tuesday night... 
light snow was falling over the Snowy Range and at times over 
the rest of Carbon and Albany counties. Earlier this morning... 
krwl had an inch of new snow and ksaa about one half inch. The 
returns on the kcys radar have been slowly increasing since 05z. 
However...as of 09z the intensity and coverage of the light snow 
on area radars was not great. Baroclinic band on satellite 
imagery was becoming less organzied early this morning as well. 
The upper low early this morning was still over south central 
Montana with most of the energy across southern Wyoming 
associated with the 300 mb jet. The associated was located from 
near klsk to between klar and kcys as of 09z. Still a large area 
of 2 to 3 mb three hourly surface rises behind the front at that 
time. The front should move through the rest of the County Warning Area by 14z. 
Models develop the middle and upper level low over northwest Kansas 
by 00z with the surface low over eastern Kansas. With that 
movement and lift from the 300 mb jet...middle level frontogenesis 
and surface forcing believe that light snow or flurries will 
spread over much of the County Warning Area by middle morning. Based on current 
radar and satellite trends have lowered the amounts to less than 
an additional inch through the morning. Larger amounts still 
expected in the Snowy Range where orographics will enhance the 
snowfall. The rest of today will be windy and cooler with some 
snow showers. The lapse rates are still expected to steepen 
with the cold temperatures aloft. Middle level convergent area 
through the afternoon would favor bands of snow showers between 
kean and kibm and outside of the mountains have the highest probability of precipitation 
in that area. Heights aloft rise over the region tonight and 
Tuesday as the storm system moves further east on the plains. 
Surface high pressure will also be over the area...centered over 
western Wyoming. The result should be dry and cool conditions 
through that time as well as a minimum of cloud cover. Models 
are all similar in depicting a shortwave trough moving into the 
northern plains Tuesday night. The feature will push a shallow 
cold front into the East Part of the County Warning Area after 06z Wednesday. At 
this time have placed the front from kpbf to kdgw by 12z Wednesday. 
Have adjusted the winds to more northerly behind the front. The 
GFS and European model (ecmwf) devlop light snow or flurries behind the fron the in 
the northeast third of the County Warning Area after 06z Wednesday. For now have 
bumped up probability of precipitation a bit for later Tuesday night in that part of the 
County Warning Area. 


Long term...Wednesday through Sunday 
preferred the European model (ecmwf) in the extended period...which seems the most 
consistent model. The GFS and European model (ecmwf) are similar early on...but then 
begin to differ by Friday evening. The 00z GFS is slower and deeper 
with the upper trough moving across The Rockies and into the plains 
than the European model (ecmwf) and also its previous run. Northwest cyclonic flow will be 
over the County Warning Area on Wednesday between an upper ridge over the western U.S. And an 
upper low moving into the central Mississippi Valley. Some thicker 
clouds will occur over the NE portion of the County Warning Area during the 
day...but will decrease towards evening. An upper ridge will be 
over the forecast area on Thanksgiving day resulting in dry and very 
mild conditions. SW flow will develop aloft on black Friday as the 
upper ridge axis moves east and an upper trough moves over the 
central and southern rockies and deepens. Very mild conditions will 
continue across the area Friday...but then a cold front will move 
across the County Warning Area late Friday night/early Sat which will cool temperatures 
significantly for Sat and sun. The upper trough will also move 
across the County Warning Area on Sat. Not very much moisture is associated with 
this system...so left very low probability of precipitation in the forecast. Seems El Nino 
may be starting to influence the weather patterns over the forecast 
area. The flow appears to split Sat night per European model (ecmwf) with north 
upper flow over the County Warning Area the result on sun. An upper low then 
develops in the southern portion of the split...over the desert SW. 
High temperatures will be around normal for Wednesday...10 to 15 degrees 
above normal for Thanksgiving and black Friday...around normal 
Sat...and 5 to 8 degrees below normal for sun. 


Aviation... 
the storm system moving across the central rockies today will 
produce at least periods of MVFR ceilings and visibilities in snow 
over much of the County Warning Area. The Snowy Range will be obscured for most 
of the day. In addition...northerly surface winds will gust as 
high as 35 knots over the East Part of the County Warning Area today. Icing will 
be a concern over the County Warning Area today especially between 8000 feet mean sea level and 
12000 feet mean sea level. VFR conditions will return to the County Warning Area this evening 
as the storm system moves onto the plains. Winds will also 
gradually decrease early tonight. A shallow surface cold front 
will move over the East Part of the County Warning Area later Tuesday night and 
may produce MVFR or IFR ceilings behind the front as well as some 
flurries. 


Fire weather... 
fire weather concerns will be minimal into the middle part of the 
week. Cool temperatures and higher relative humidities will persist 
through that time along with some light snow today. Northerly winds 
will gust as high as 40 miles per hour over much of the area today. The 
warmest and driest days this week will be Thanksgiving day and 
Friday. 


&& 


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


&& 


$$ 


Short term/aviation... 
long term... 

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