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fxus63 klsx 240218 
afdlsx 


Area forecast discussion...updated 
National Weather Service St Louis MO 
918 PM CDT Wednesday Jul 23 2008 


Update... 
/913 PM CDT Wednesday Jul 23 2008/ 
updated forecast to increase cloud cover overnight based on 
extensive area of middle and high clouds moving southeast out of Iowa. Also 
upped probability of precipitation into the chance catergory in the far northwestern part of the 
County Warning Area as past few runs of RUC are showing decent 925-850mb forcing 
on the edge of 500-1000mb MUCAPES using 850mb parcels. Also 
trimmed lows a bit in the southeastern part of the County Warning Area as temperatures are 
falling off pretty quickly and dewpoints are near 60. 


Britt 


&& 


Discussion... 
/353 PM CDT Wednesday Jul 23 2008/ 
surface ridge centered over the Great Lakes is pumping unseasonably 
cool and dry air into County warning forecast area. Temperatures have only risen into the upper 
70s to low 80s by 300 PM with dewpoints generally in the 50s. Heat 
and humidity is not that far away though with Joplin reading 91/72 at 
200 PM. As the surface ridge drifts east through the end of the 
week we'll see the moisture encroach back into central and eastern 
Missouri. Northwest flow aloft due to the trough over the Great Lakes 
and the elongated ridge over the plans and southwest will allow 
several shortwaves to ripple southeast across the area. These waves 
combined with an active low level jet are setting up the potential 
for a wet pattern starting Thursday and continuing at least through 
Friday...and potentially into Saturday as well. Operational models 
are in pretty good agreement that there will be 2 or 3 mcs's to 
affect mainly northern and central portions of the area...but 
nailing down the specifics is difficult this far out. It looks like 
starting the rain tomorrow will be the result of nocturnal 
convection tonight over eastern Nebraska and Iowa that will roll 
down into northeast Missouri and western Illinois late tonight or 
early Thursday morning. Resulting mesoscale convective vortex will continue to provide a 
focus for daytime convection to continue during the day. Have bumped 
probability of precipitation up to likely/high chance across much of the northern and 
western portions of the County warning forecast area. Another mesoscale convective system looks likely to develop 
somewhere over southern Iowa/northern Missouri Thursday night and it 
should roll east/southeast affecting portions of the bi-state area 
through Friday morning. Of course...outflow boundaries will likely 
provide foci for additional thunderstorm development Friday 
afternoon. This pattern could continue through much of the weekend 
as the low level jet continues to undercut persistent northwest flow 
aloft...though I think the primary mesoscale convective system track will stay north over Iowa 
and central and northern Illinois. 




Carney 


&& 


Aviation... 
/606 PM CDT Wednesday Jul 23 2008/ 
for the 00z tafs... 
ridge of high pressure will dominate our weather pattern tonight 
before moving off to the east later Thursday. VFR weather will 
continue through the period except in scattered thunderstorms that 
may affect the taf sites on Thursday. Convection is expected to 
roll down out of Iowa on Thursday. 


Tps 


&& 


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


$$ 


Weather forecast office lsx