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fxus63 kunr 192104 
afdunr 


Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
302 PM MDT Friday Mar 19 2010 


Discussion...20z surface analysis shows high pressure building into the 
area from the northwest. Upper analysis shows upper trough from 
Hudson Bay diagonally across South Dakota into Colorado. Instability 
due to the upper trough and steep low level lapse rates has resulted 
in cloudy skies and isolated snow showers. 


Winds will diminish this evening as high pressure builds into the 
area and the surface pressure gradient relaxes. The upper trough will 
continue to shift southeast...leading to decreasing clouds this 
evening and an end to any snow showers. Temperatures will be cold 
tonight...with lows in the teens to lower 20s. 


On Saturday and Sunday...an upper ridge will build over the northern 
plains...leading to a pleasant and dry weekend. The thermal ridge 
becomes well-defined Sunday...leading to highs in the middle 50s to 
lower 60s at most locations. 


Extended...weak ridge will pass east of the region on Monday as 
upper trough digs southeastward across the intermountain west. Mild 
temperatures can be expected Monday...with highs in the 50s and 60s. Weak 
upper level energy ahead of the trough and an approaching cold front 
could bring a few showers to northern and western portions of the 
County Warning Area late Monday into Monday night. Would not rule out a thunderstorm 
or two as well...but will not include the possibility at this point. 


Medium range models coming into reasonable agreement with upper 
trough/low sliding well south and west of the area Tuesday into 
Wednesday. Bulk of precipitation will likely stay south and west of the 
County Warning Area...so will lower and trim back probability of precipitation some...especially across 
northern and eastern portions of the County Warning Area. Will keep low probability of precipitation across 
portions of the County Warning Area Tuesday into Tuesday night. Cooler air will 
build into the area for Tuesday and Wednesday. Will keep dry and 
seasonably mild conditions for the latter part of next week. 


&& 


Aviation...areas of MVFR ceilings will linger into early this 
evening...with clearing skies overnight. Breezy northwest winds 
will also diminish early this evening. 


&& 


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


$$