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Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
1122 PM CDT Monday Oct 6 2008 


Discussion... 
/216 PM CDT Monday Oct 6 2008/ 
longwave trough located across the plains will progress east toward 
the Midwest over the next 24 hours. Current radar and satellite show 
a well established warm conveyor belt across eastern Kansas and 
Oklahoma. 


This current line of showers and thunderstorms that are well removed 
from the synoptic cold front are in response to the first shortwave 
lifting to the northeast from the base of the trough. This activity 
will continue to slowly move to the north-northeast and affect 
mainly locations to the west of the County Warning Area this evening. 


Another shortwave/speed maximum will round the base of the trough tonight 
and initiate additional convection just south of the forecast 
area across extreme southern Missouri...Arkansas...etc. This will 
likely disrupt the current warm conveyor belt and lead to a break 
in precipitation further north. This may further delay 
precipitation onset across the northern portion of the County Warning Area until 
Tuesday morning. 


On Tuesday...upper trough finally moves through...with each model 
having their own idea of how the middle-level and surface features will 
evolve. Regardless of what solution verifies...it looks to be a cool 
and wet day across the majority of the area. Given extensive cloud 
cover that is forecast by all model guidance...instability should be 
limited and severe weather chances small...even with impressive 
shear. Precipitation should come to an end Tuesday night as the trough 
moves east. 


Cloud cover will decrease from west to east on Wednesday with 
temperatures remaining seasonably cool. Zonal flow aloft and high 
pressure in the wake of this system will lead to a gradual warming 
trend Thursday and Friday...with relatively cool autumn nights. 


Extended...Friday through Monday 


Have trended forecast to the more steady ecwmf solution. Large scale 
pattern to amplify with an upper trough digging across the western 
Continental U.S. And then moving east toward the Midwest. Ensemble spread from 
GFS is huge and 06z output seems spurious with large cutoff upper 
low across the Central Plains on day 7. European model (ecmwf) lifts core of upper 
low northeast across upper plains late next weekend with a cold 
frontal passage across the County Warning Area Sunday night/Monday. Above normal 
temperatures are forecast through the extended period with no 
mention of precipitation. 


Cvking 


&& 


Aviation... 
/1107 PM CDT Monday Oct 6 2008/ 
for the 06z tafs...mid-hi level clouds continue to stream northeastward through the 
County Warning Area this evening ahead of middle-upper level trough over the plains. First batch 
of rain has moved into cou and should move into stl/sus around 06z 
and in uin around 07z. This precipitation so far was not reducing visibilities to 
MVFR conditions and was mainly falling out of middle level clouds. 
Looking at model relative humidity guidance and MOS cloud ceiling height forecast will 
lower ceiling down to around 2000 feet in cou by 12z and in uin...stl 
and sus by 15z. Should get one or two more periods of rain on Tuesday 
and this should be heavier with embedded thunderstorms and rain. Southeasterly surface winds will 
continue at the taf sites...eventually shifting to a westerly direction in 
cou by 00z Wednesday after the passage of the cold front. 


Gks 


&& 


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


$$ 


Weather forecast office lsx