835 
fxus63 kfsd 232013 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota 
315 PM CDT Wednesday Jul 23 2008 


Discussion... 


Difficult forecast scenario setting up across forecast area this 
evening. Complex of slowly decaying showers and thunderstorms 
shifting southeast on the edge of upper level ridge across the 
Western Plains. Have left highest probability of precipitation this evening across southern 
County Warning Area with 850-800 mb warm air advection/frontogenesis lingering 
through the evening hours. Attention then shifts to the west as a 
series of weak waves shift through the area under weak zonal flow. 
18z unr sounding is fairly unstable with 1500 j/kg of cape. Nice 
moisture tongue of upper 60 to near 70 degree dew points extending 
from Phillip to Faith South Dakota. Thunderstorms starting to 
develop across the Black Hills...and expect coverage to become more 
widespread throughout the late afternoon/evening. Remnants of this 
activity may shift into western portions of forecast area after 
midnight...but do not expect anything to be severe given 
stabilization of airmass today. With southeast flow drawing moisture 
into the region...expect lows to mainly be in the middle and upper 60s. 
A few locations in far northeastern County Warning Area may fall into lower 60s as 
long as southeast flow draws drier air across Iowa north. 


Any thunderstorm activity Thursday morning will likely be limited to southeastern County Warning Area through middle 
morning and then end until later in the afternoon as cold front sags into northwestern 
County Warning Area by late afternoon/Erly evening. Fairly unstable airmass prognosticated by 
models...but big question if cap can be broken as lwo level southeasterly 
flow may keep low levels from mixing out completely. However...if it 
can break cap...then will see a better chance of severe storms with hail and 
wind the main threat. Also could see small chance of thunderstorm continue far southern County Warning Area 
near 850 mb boundary over Nebraska and Iowa through the day. So for Thursday afternoon will keep 
small chance northwestern County Warning Area and far southern County Warning Area and then spread chance of thunderstorm southeastward 
across County Warning Area Thursday night as fnt sags across County Warning Area. Fnt should pass Thursday most of 
County Warning Area...but pbly stall near southern County Warning Area or just to the S Friday and Friday night. 
This boundary could continue to trigger a few thunderstorm through Friday night across far southern 
County Warning Area. For now Sat looks dry during the day...and then fnt tries to 
lift northward slightly in response to a weak short wave in the northwest flow. So will 
bring another chance of thunderstorm Sat night into sun with best chance across far 
southern County Warning Area near MO rivr. With westerlies across the County Warning Area into Erly next week can 
not rule out more rounds of scattered thunderstorm with models hinting at a chance Monday 
night into Tuesday. 


Temperatures on Thursday shd rebound from todays rain cooled airmass with 80s most 
places. Behind fnt on Friday should see better mixing and temperatures will be 
warm again. Will not deviate too much from climatology for maximum temperatures this 
weekend but if precipitation Sat night into sun is a little more widespread...then 
sun could be as cool as today. 


&& 


Aviation... 
mainly VFR conditions expected through forecast period. Complex of 
showers with embedded thunderstorms will slowly slide southeast this 
evening exiting the tri-state region visibilities may briefly fall 
into the MVFR category with the strongest storms. Additional storms 
may be possible near the Missouri River valley after 05z 
Thursday....but should rapidly dissipate as they attempt to work 
east Thursday morning. 


&& 


Fsd watches/warnings/advisories... 


South Dakota...none. 
Minnesota...none. 
Iowa...none. 
NE...none. 


&& 


$$ 
Bt/