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Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
330 PM CDT Friday Mar 19 2010 


Discussion... 
north winds will gradually decrease through the overnight hours as 
high pressure builds into the western Dakotas. Drier push of air 
will result in a net decrease in clouds...especially after midnight. 
With cool dry airmass in place...expect temperatures to fall a few 
degrees below seasonal norms in the upper teens and lower 20s. 


As high pressure continues to build into the northern plains expect 
skies to clear from north to south. Could see some diurnally 
driven cumulus develop on the back edge of the cloud layer. As surface 
ridge moves into central South Dakota...expect north winds to become 
light limiting mixing potential some. Regardless...will be a fairly 
cool day with 850 hpa temperatures around -6 to -9 c. Models suggest some 
late day warming across the western County Warning Area...though highs should still 
remain well below climatological norms. 


Warmer day on Sunday expected as Chinook type pattern develops 
resulting in a warm westerly flow. Forecast area located well to 
the north of strong low pressure system over southern Mississippi 
River valley...and should see a light westerly wind. 


Light winds and clear skies continue Sunday night into Monday...and 
may see some radiational fog develop...especially in low lying river 
valleys. Have not mentioned in the forecast at this point as it is 
still a few days away. Warm southerly wind develops across the 
northern plains on Monday as a Lee side trough develops along the 
eastern side of The Rockies on Monday in response to a series of 
phased waves translating from the west. Main jet energy remains 
focused well to the south...and latest model trends have continued 
to move the middle level forcing across the Central Plains. As a 
result...have dropped mention of probability of precipitation with this system with 
exception of northwest Iowa during the daytime hours of Wednesday. 
Confidence in that is relatively low...with only a slight chance 
mention. 


Cooler conditions expected on Thursday as Arctic high noses into the 
area from the north. Airmass shifts east on Friday allowing for a 
warming trend...however...open shortwave is expected to move across 
the northern plains potentially creating some light rain. Models 
are in surprisingly good agreement with this system. Appears as 
though the crux of the wave will remain focused to the north...but 
may brush northern tier or two of counties especially in southwest 
Minnesota. 


Overall...an up and down week temperaturewise...but the mostly dry 
conditions will help area rivers continue to recede. /Bt 


&& 
aviation... 
expect MVFR ceilings to slowly improve to VFR later tonight as drier air 
intrudes from the north and breaks up stratus layer. Into tomorrow 
morning...will continue to see dissipation of higher level clouds 
and taf sites trending towards sky clear. /Laflin 


&& 


Fsd watches/warnings/advisories... 
South Dakota...none. 
Minnesota...none. 
Iowa...none. 
NE...none. 


&& 


$$