263 
fxus63 kunr 231724 
afdunr 


Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
1024 am MST Monday Nov 23 2009 


Discussion...17z surface analysis shows low pressure over 
northeastern South Dakota with high pressure over southern Idaho and 
Utah. Tight surface pressure gradient over northeastern Wyoming and 
western South Dakota will result in breezy/windy conditions today. 
Upper analysis shows the upper low spinning over northwestern 
South Dakota. Cloud cover had been increasing over the forecast 
area due to the upper trough but now it appears that the axis of 
the upper trough has shifted into western South Dakota...with 
subsidence breaking up the stratus to the west of the trough line. 
Anticipate more forecast updates today to adjust sky cover and 
precipitation chances as the upper low moves east of the region. 


&& 


Aviation...isolated -shra or -shsn will be found today as an upper 
level disturbance moves through. Most areas will remain 
VFR...though some areas of MVFR ceilings may be possible over the 
Black Hills and parts of central South Dakota. 


&& 


Previous discussion... /issued 243 am MST Monday Nov 23 2009/ 


Discussion...09z surface analysis had weak low over the Black 
Hills with cold front into Colorado and trough into eastern Montana. These 
features a reflection of upper level trough from Montana into Colorado. One 
wave over Montana...but main wave starting to take over in southwest Wyoming 
in response to 90kt jet digging into base of trough. This wave 
will close off as upper low over Kansas tonight. With main forcing now 
further south...have tempered probability of precipitation for today/tonight...especially 
in the south. We/ll see low coverage -shsn today/tonight...with 
mixed -shra this afternoon. Best chances will be along the far 
southern borders of the County Warning Area. Temperatures near guidance. 


Tuesday...transient short wave ridge will bring some 
sunshine...but next fast moving upper level trough will already be 
impacting ND/Montana by evening. Moisture/forcing on tail end of wave 
sufficient for a chance of -shsn Tuesday evening. Breezy spots 
also as cold front brings cold air advection...especially in the 
east. Temperatures near guidance. 


Wednesday...upper trough spins as upper low into Illinois. Upper ridge 
builds over The Rockies...beginning to affect the County Warning Area. Temperatures 
near guidance. 


Extended...an upper level ridge will keep conditions warm and dry 
through Friday afternoon. Next upper wave moves over the West 
Coast Friday and starts pushing east this weekend. This will bring 
cooler temperatures and possibly some precipitation. 


&& 


Unr watches/warnings/advisories... 
South Dakota...none. 
Wyoming...none. 
&& 


$$