707 
fxus63 kunr 200814 
afdunr 


Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
214 am MDT sun Jul 20 2008 


Discussion...08z surface analysis had weak low near kabr with 
meandering frontal boundary into NE and then into Wyoming. P6sm sky clear 
over the County Warning Area...still might see some altocumulus castellanus/isolated thunderstorms and rain early this 
morning with modest 850-700mb Theta-E advection in the south. Will 
make last minute adjustments to cover if needed. 


Today through Tuesday...upper level ridge builds over the northern 
plains with slowly warming middle-level temperatures and subsequent 
cap. This may keep eastern portions of the County Warning Area free from convection 
for much of the period. However...further south and west nearest 
surface boundary and higher terrain...can expect small chances for 
convection. Best chances will be tonight as low level jet sets up 
potential for mesoscale convective system along the South Dakota/NE/WY border...moving east of the 
County Warning Area overnight. Shear will be sufficient each day for severe 
thunderstorms...if storms develop. Potential temperatures in the 
middle 90s next three days...but easterly component to winds 
today/Monday will keep things a bit cooler. Tuesday main 
temperature concern as winds may go downslope as Lee trough shifts 
east and thermal ridge peaks. Will go conservative for now...but 
could be well into the 90s if things work out. 


Extended...an upper level ridge will remain over the plains for much 
of next week. This ridge will bring slightly above average temperatures. A 
series of weak disturbances will pass over the ridge and may bring a 
few thunderstorms to the area each day. The best chance of 
thunderstorms should be on Wednesday when a weak Pacific trough and 
a cool front cross the northern plains. 


&& 


Aviation...VFR conditions will continue across the area today. A 
few storms are possible late this afternoon and evening...mainly 
across southern South Dakota and Nebraska. Local MVFR conditions can 
be expected near any storms. 


&& 


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


$$ 


Helgeson/trimarchi