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fxus63 kunr 211611 
afdunr 


Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
1011 am MDT sun Mar 21 2010 


Discussion...forecast remains on track. No updates planned at this time. 


&& 


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


&& 


Previous discussion... /issued 145 am MDT sun Mar 21 2010/ 


Discussion...water vapor shows large upper ridge over the northern rockies 
extending into the northern plains. Some thin cirrus spilling over the 
ridge...but otherwise mostly clear skies across the northern plains. At the 
surface...Lee trough developing along the eastern slopes of the northern/central 
rockies. 


Today...mostly sunny skies expected...with temperatures warming into the 
50s to middle 60s under thermal ridge. 


Monday...upper ridge flattens as upper trough works into the northern rockies. 
Cold front will push into our County warning forecast area during the day...but not before temperatures 
warm well into the 60s especially on the South Dakota plains. Jet streak 
associated with upper trough will pass overhead during the afternoon/evening hours 
for an increasing chance of -shra especially over our western zones. Should 
be enough instability for a thunderstorm or two as well. Rain will mix with 
snow overnight as cooler air filters in. 


Tuesday...upper trough axis crosses our County warning forecast area during 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 ridging will build in from the west as western 
Continental U.S. System slides southeast across the Southern Plains during the 
middle part of the week. Dry weather and mild temperatures will 
return for Wednesday and Thursday. Some unsettled and cooler weather 
could return for the end of the week and into the weekend as models 
show a backdoor cold front and upper level wave crossing the area. 
Will hold off on adding probability of precipitation until there is better consistency. 


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


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