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Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
1252 PM CDT Thursday Aug 21 2008 


Discussion... 
/528 am CDT Thursday Aug 21 2008/ 
a large batch of rain with embedded showers was moving northward through the 
County Warning Area early this morning. This precipitation was ahead of a shortwave trough moving northward 
through eastern MO...and in an area of 850 mb warm air advection...moisture converge...and 
Theta-E advection associated with a S-southeasterly low level jet. This batch of rain 
may move north of the County Warning Area by lt morning but should have more rain showers and a 
few thunderstorms and rain as more shortwaves continue to rotate northward through the area east of 
the middle-upper level low currently over central Kansas. This middle-upper level low 
will open up and weaken and move north of the County Warning Area tgt. Precipitation may be more 
scattered tgt and Friday but will still have a chance of rain showers/thunderstorms and rain with 
another middle-upper level low centered over eastern OK and southerly low level flow 
continuing to bring low level moisture northward through the County Warning Area. With low level 
cloud cover today and periods of rain maximum temperatures will be unseasonably 
cool this afternoon. Maximum temperatures should be warmer on Friday afternoon with more 
breaks in the cloudiness...less coverage of precipitation and continued southerly 
low level flow and warm air advection on the western periphery of the surface/850 mb ridge. 
May have a short break in the rain chances Friday night...but the 
probability of rain will increases Sat and Sat night as a northern stream 
shortwave trough moves eastward through the northern plains sending a cold front southeastward 
into northern MO. Should have at least scattered rain showers/thunderstorms and rain along and just S 
of the fnt as the models indicate it will get relatively unstable by 
Sat afternoon. There will also continue to be a weakness in the middle-upper level 
heights over the County Warning Area with an middle-upper level ridge over Colorado and nm west of 
MO and another middle-upper level ridge over the northestern US and middle Atlantic 
region east of MO. Maximum temperatures should continue to warm on Sat with highs near 
normal. 


Gks 


&& 


Aviation... 
/1241 PM CDT Thursday Aug 21 2008/ 
for the 18z tafs...difficult ceilings to forecast this afternoon and into the 
remaining period. Upper level low continues to slowly eject northeastward across the Maryland 
msvly. Rain showers developing across much of MO at present resulting in MVFR to 
IFR conditions across all taf locations. In keeping with persistance 
with previous forecast expect thunderstorms in the vicinity across all sites with ceilings lifting 
over the region into the evening hours...have also the chances of reduced 
visibilities and ceilings attendant with any rain showers that may impact. Into the 
morning visbys and ceilings shld lower in concert with sufficient surface 
and low level moisture and diurnal cooling. This on the basis of 
conditions that developed across Arkansas Erly this morning. Visibilities 
shld fall into the 1-2sm category with ceilings ovc008-015 and thus 
into IFR conditions. 


Sipprell 


&& 


Lsx watches/warnings/advisories... 
MO...none. 
Illinois...none. 
&& 


$$ 


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