617 
fxus63 kfsd 201111 
afdfsd 


Area forecast discussion for southeast South Dakota/southwest Minnesota/northwest Iowa 
National Weather Service Sioux Falls South Dakota...corrected 
610 am CDT sun Jul 20 2008 


Discussion... 
moist surface and light winds lending to fog formation over portions of 
the area. Bulk of the fog across SW Massachusetts and northwest Iowa with some locals 
seeing visibilities reduced to less than a quarter mile. Not 
anticipating an advisory and dense fog is rather sparse in coverage 
and for will rapidly burn off with sunrise. 


Minimal amounts of convection over the northern plains this morning. A few 
thunderstorms into eastern ND with upper wave...and a few others in 
central Iowa...which fired along the midlevel boundary. Chances for 
thunderstorms in the County Warning Area this morning on the low side. Models 
continue to indicate srly return flow at the midlevel across the MO 
valley after 12z this morning. Have left low end chance probability of precipitation given a 
decent thetae push...but convection development not diurnally favored 
this morning...and models may be a bit aggressive in return flow this 
morning. Thetae advection pushes east into northwest Iowa later this morning 
into early afternoon. Expecting a good deal of sunshine to juice up 
the boundary layer this afternoon...providing at least a small chance 
of late afternoon/early evening thunderstorms across the 
County Warning Area...however...there should be a weak cap in place and some 
subsidence as surface high builds across the north. Best chances will be 
along the MO river into northwest Iowa...near the surface boundary. Sufficient shear 
and cape...especially near the surface boundary for the development of 
rotating supercell thunderstorms for late afternoon into the evening. 
Mu convective available potential energy in the 2000 to 4000 j/kg support vigorous thunderstorm 
updrafts capable of producing hail to the size of Golf 
balls...although freezing levels around 15000 feet will minimize the 
chances for even larger hail. There is also the threat for 
thunderstorm winds of around 70 miles per hour...and the outside chance for a 
few tornadoes near the surface front. 


Thinking the best chances for storms will be late this evening and 
after midnight in the southeastern County Warning Area...as a weak low level jet kicks and 
interacts with midlevel boundary sliding southward. There will be the 
continued threat for severe weather with these storms. Also somewhat 
concerned with the potential for flash flooding. Middle/upper flow 
perpendicular to low levels...which could lead to backbuilding 
storms tonight. Precipitable waters  of 1.5 to 2 inches and moist srly flow will 
provide the potential for heavy rains. At this time...it looks like 
the heaviest rains will be S of the County Warning Area...but just depends on where 
the surface boundary set up this evening. 




&& 


Aviation... 
areas of fog and stratus...especially near fsd and sux...will creep 
into the IFR category at times prior to 14z. After this...expect the 
full effect of the sun to burn off any fog and VFR conditions should 
persist into the afternoon. By late afternoon into the 
evening...thunderstorms could fire along a front that shifts north 
towards the Missouri River. If thunderstorms can develop...sux would 
see the highest probability of thunderstorms...some of which could 
produce brief IFR conditions in very heavy rain. 


&& 


Fsd watches/warnings/advisories... 


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


&& 


$$ 
Liebl