341 
fxus63 kfsd 212032 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
330 PM CDT Thursday Aug 21 2008 


Discussion... 
brisk low level south-southeasterly flow of moist air in County Warning Area tonight...with tightest 
gradient west and north in County Warning Area. Deepest moisture in southeast County Warning Area where will keep 
small chance -shra this evening...becoming chance -dz after midnight as air mass cools 
and upper trough pulls off to the east bringing middle level drying from the 
west. Widespread SC deck southeast of line from Hon to onl this afternoon should break 
up some this evening in western and northestern portions where it is more diurnally 
driven. However...with overnight cooling expct stratus and some 
areas of light fog to redevelop east of James River by late tonight. 


Cold front will rapidly move across the County Warning Area tomorrow. Model timing 
of front a bit faster then previous runs. Now looks like the best 
chance for thunderstorms will be in far southeastern County Warning Area tomorrow 
afternoon/early evening...provided front does not speed up 
anymore...and the cap can be broken. Should storms develop...a few 
storms would become severe. Ahead of the cold front...an abidance of 
low level moisture will be in place...such that low clouds and light 
fog should be prevalent. Visibilities should remain in the 2-4 sm 
range so not mentioning fog in the grids. In addition...expecting 
light mist to accompany light fog. Once the front blows 
through...much dryer air will surge ewrd. A little concerned winds 
in the west could be pretty strong...model may be underdoing the height 
of mixing and there will be very strong winds just above this level. 
Did bump up winds over guidance...but not as strong as appears 
possible. Also...very dry behind the front...so lowered dew points a 
good deal...but like the winds could mix down even lower dew 
points. 


Dry through rest of the weekend with high pressure and dry air in 
place. With mostly clear skies and light winds...lowered the 
overnight lows a bit through the weekend...which will generally fall 
into the 50s. Beginning of next week it becomes a bit more tricky. 
Middle level boundary begins to work NE into the area. GFS indicates quite 
steep lapses rates developing into the western County Warning Area Sun night...along 
with isentropic forcing. 


&& 


Aviation... 
MVFR ceilings southeast of line from Yukon to fsd to otg this afternoon gradually developing 
back nwwd during night. Becoming IFR ceilings and areas MVFR visibilities in br by 09z 
southeast of line from Hon to onl. Brisk southerly winds gusting around 30 kts in northern 
and western portions of County Warning Area this afternoon and early evening...decreasing overnight. 


&& 


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


&& 


$$ 


Liebl/ryrholm