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Area forecast discussion 
National Weather Service St Louis MO 
351 PM CDT Thursday Aug 21 2008 


Discussion... 
/349 PM CDT Thursday Aug 21 2008/ 
upper trough remains over cntl plains this afternoon. This trough will continue to 
slowly move northeastward while numerous short wave rotate through the area tonight and 
tomorrow. This system will continue to bring rain showers to the area through tomorrow. 


Widespread rain has become more cellular and rain showers as middle level dry air 
is advected into the region. Some thunderstorms and rain have also developed across the 
MO and Illinois region. These rain showers should dissipate somewhat this evening. 
However...rain showers should continue over much of the area during the night. Models 
indicate tonight should evolve into a stratus event rather than fog 
developing. 


Local WRF model indicates a similar solution for tomorrow with widespread 
rain showers/thunderstorms and rain developing mainly in the afternoon hours. Other models do not have 
as much development and have therefore kept probability of precipitation for tomorrow a little 
lower than today. 


Cold front should reach portions of northern County Warning Area during the day Sat. This cold front 
will bring another chance of thunderstorms and rain to the region this weekend before 
washing out and stalling across portions of southern MO. There is still a 
lot of uncertainty how far S the cold front will make it. Much of this 
depends on track of Fay remnants. Have little confidence in models 
solution for this system as models have little continuity from one run to 
the next. Latest track forecast from TPC/NHC has rather large 5-day forecast 
Cone across the southern US...which brings it as far north as southern MO. 


Have undercut or trended toward cooler MOS into the weekend as cloud cover 
and rain showers should keep temperatures down tomorrow and Sat. 


At this time...have kept forecast dry beyond Monday as European model (ecmwf) keeps remnants of Fay 
further east. Surface high should build into the region sun and into early 
next week. This surface ridge should bring cooler and drier air to the 
area. Forecasted temperatures in extend are blw MOS and trended toward the ensemble 
mean temperatures. Is still some uncertainty due to poorly forecasted track of 
Fay by the GFS and European model (ecmwf). However...have trended forecast toward the European model (ecmwf). 




Tilly 


&& 


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. 
&& 


$$ 


Weather forecast office lsx