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afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
300 am MST Sat Nov 22 2008 


Short term...today through Sunday night... 


Today...if you Love mild late November days with minimal amounts of 
wind...today is your day. Zonal flow aloft with almost no cloud 
cover and whatever cloud cover forms will be of minimal opacity. 
Surface through 700 mb gradients will be relatively weak for this 
time of year...thus minimal wind. Maximum temperatures in the middle 
40s to near 60 with 700 mb temperatures near 2 celsius and 1000-500 
mb thicknesses near 5550 meters. 


Tonight...next progressive and low amplitude positively tilted 
shortwave trough aloft moves across Wyoming spreading middle and 
high clouds with high level of opacity across our 
counties...especially west of Interstate 25. Will also see a Pacific 
maritime oriented cold frontal passage. Both NAM and GFS keep quantitative precipitation forecast 
west of our counties which looks reasonable considering mesoscale 
and synoptic features. Minimum temperatures will be relatively mild 
due to cloud cover and decent low level winds and mixing. 


Sunday...progressive shortwave trough aloft moves into the Central 
Plains states. GFS has been doing better with quantitative precipitation forecast depiction so far 
this season and thus have gone with its depiction of greatest quantitative precipitation forecast 
and morning precipitation from Carbon County through Albany County 
where best orographics...deepest moisture and synoptic lift 
associated with the 500-300 mb and 700-500 mb quasigeostrophic 
forcing will coincide. Drying in the afternoon in the wake of the 
shortwave trough aloft passage. Cooler day but still seasonable with 
maximum temperatures in the 40s as 700 mb temperatures fall to -6 
celsius and 1000-500 mb thicknesses fall to 5460 meters. 


Sunday night...clear and quiescent overnight as northwest flow aloft 
develops in advance of approaching shortwave ridging across Idaho 
and Utah. Nighttime minimum temperatures in the teens and 20s with 
clear skies...light winds and excellent radiational cooling. Rubin 


Long term...Monday through Friday...mild and dry Monday and Tuesday with relatively 
light winds as large upper ridge shifts slowly across the region. 
It looks like there will be some clouds shifting over the area mainly on 
Tuesday as the flow aloft becomes more SW. Pattern becomes more 
interesting later in the week though as a series of Pacific systems moves 
into the western U.S. 22/00z run of the European model (ecmwf) looks out of sync with 
its previous run and other models and generally discounted. 21/12z 
European model (ecmwf) fits a little better with other models...21/00z ecwmf was 
probably the best fit. GFS ensemble mean is looking real consistent 
with the first system which reaches the region late Wednesday night into 
Thursday. 00z GFS operational run may be a little too far north with the 
movement of this first system based on its ensemble of 700 mb heights. 
It still looks like there will be a chance of some light snow over 
much of the region Thursday into Friday with this first system. Inherited 
probability of precipitation of 20-30 look good for starters at this point. Temperatures stay up 
above normal on Wednesday...then drop back to near or below normal by Friday. 


&& 


Aviation...VFR today and tonight. MVFR and IFR in showers across 
Carbon and Albany counties Sunday morning with MVFR there Sunday 
afternoon. VFR elsewhere on Sunday. Rubin 


&& 


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


&& 


$$ 


Short term/aviation...Rubin