Weather

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Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
1136 PM CDT Wednesday Aug 27 2008 


Update... 
/1016 PM CDT Wednesday Aug 27 2008/ 
surface dewpoint temperatures are higher than earlier forecast. 
Have therefore addded in some patch fog south of the Missouri 
River/I-64 corridor for the overnight hours. No other changes made 
to going forecast at this time. 


Carney 
&& 


Discussion... 
/214 PM CDT Wednesday Aug 27 2008/ 
a cold front that currently stretches from the Central Plains to the 
upper Midwest will move southeast over the next 36 hours...bringing 
a good chance of thunderstorms to at least the northern half of 
the County Warning Area Thursday afternoon and evening. An unstable airmass will 
build ahead of the front on Thursday as the flow becomes 
southerly. Dewpoints in the middle to upper 60s and temperatures in 
the upper 80s will contribute to cape values between 1500 and 2500 
j/kg. Expect that convective initiation will take place north of 
the forecast area across southern Iowa tomorrow afternoon. 
Clusters/lines of strong/severe storms will move south with the 
cold front into northeast Missouri and west central Illinois 
during the late afternoon and early evening hours. 


The loss of daytime heating/instability throughout the evening will 
likely lead to a weakening trend to the convection as it heads 
further south. Only caveat is that a weak low level jet may aid in the 
development of new convection overnight as the front slowly sags 
south through the forecast area. If current trends of convective 
development within mesoscale models continue...probability of precipitation will need to be 
increased tomorrow afternoon and evening. 


High pressure will build across the Midwest for the Holiday 
weekend. Mostly sunny conditions and very comfortable 
temperatures/humidity can be expected as we close the books on 
another Summer vacation season. 


Questions abound in the extended as tropical storm/Hurricane Gustav 
will surely slow down the mean flow across the United States next 
week and delay the progression of any shortwave in the westerlies. 
GFS failed to initialize Tropical Storm Gustav again...so have 
followed the ecwmf. A large ridge of high pressure at midlevels 
across the forecast area early next week will equate to seasonal 
temperatures and dry conditions. Must keep a watchful eye on Gustav 
for the second half of next week and the following weekend as 
current forecast trajectories would send the tropical disturbance up 
the Mississippi River valley. 


Cvking 
&& 


Aviation... 
/1122 PM CDT Wednesday Aug 27 2008/ 
for the 06z tafs...VFR conditions expected through most of the 
forecast period with lower VFR ceilings affecting KUIN and kcou towards 
end of forecast period due to frontal boundary approaching the 
area. In the short term...will keep a tempo group for shallow fog 
at ksus after 08z to mimic what happened last night. As for rest 
of sites...not sure how much fog will develop...though dewpoints 
rising nicely into the middle to upper 60s. For now will only mention in 
tempo group for kcou. Generally light and variable winds through 
this morning will become southwest after 15z. Front to begin 
moving through County Warning Area later tonight. Have front moving through KUIN 
around 02z and kcou around 04z. Will see precipitation chances with 
front...but not confident on coverage...so for now will not 
mention in tafs. 


Byrd 
&& 


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


$$ 
Weather forecast office lsx