261 
fxus63 kunr 212032 
afdunr 


Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
232 PM MDT sun Mar 21 2010 


Discussion...20z surface analysis shows low pressure over southern 
Alberta/Saskatchewan with high pressure from southern Minnesota 
into western Kansas. Water vapor image shows a large upper ridge 
east of the northern rockies with thin cirrus spilling over the top 
of the ridge and over the forecast area. Westerly winds...sunshine 
and warm air aloft have combined to push high temperatures into the 
middle 50s to lower 60s across most of the forecast area this afternoon. 


The weather tonight will be quiet with just some thin cirrus and low 
temperatures ranging from the lower 20s to the lower 30s. 


On Monday...the warm upper ridge will get flattened and rudely 
shoved off to the east as an upper trough drops into the northern 
rockies. A cold front will cross the forecast area during the 
day...but not before temperatures warm into the middle 50s to middle 60s with the 
warmest temperatures ahead of the front over south central South Dakota. 
Breezy/windy conditions are expected behind the front. A 
jet streak associated with the upper trough will pass overhead 
during the afternoon/evn hours for an increasing chance of -shra 
especially over the western zones and along and near the frontal 
boundary. With cape up to 250 j/kg very little cin and forcing near 
the front expect there will be enough instability for a few 
thunderstorms to develop as well. Rain showers will mix with...or 
turn to... snow showers overnight as cooler air filters in. 


On Tuesday...the upper trough axis will cross the forecast area 
durin the day resulting in lingering -shrasn. Temperatures will be 
noticeably cooler with highs only in the 30s to middle 40s. Any precipitation 
should come to an end Tuesday night. 


Extended...weak upper level ridging will build in from the west 
during the middle of the week as western Continental U.S. System slides 
southeast across the Southern Plains. Dry weather and seasonably 
mild temperatures are expected for Wednesday and Thursday. Some 
unsettled and cooler weather will likely return by the weekend as medium 
range models are more consistently showing a backdoor cold front and 
upper level wave crossing the area. Have added some low probability of precipitation for 
Friday into Saturday. 


&& 


Aviation...VFR conditions can be expected through the forecast 
period. 


&& 


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


$$ 
Gr/St