383 
fxus63 klsx 182043 
afdlsx 


Area forecast discussion 
National Weather Service St Louis MO 
343 PM CDT Friday Jul 18 2008 


Discussion... 
/341 PM CDT Friday Jul 18 2008/ 
much of the forecast is still based on persistence. However...the forecast 
is complicated into the weekend due to mesoscale convective vortex that has finally made it 
far enough S that it is influencing the County Warning Area. 


Mesoscale convective vortex over southern Nebraska and northwestern MO continues to produce thick middle level clouds across 
much of western MO and eastern Kansas. These clouds have kept temperatures in the upper 70s 
to low 80s. Models suggest a similar solution across the County Warning Area for tomorrow. Think 
the main vorticity maximum will be across northern/eastern Illinois around noon tomorrow which should 
allow temperatures to climb into the lower 90s again even with convective debris 
over the area. 


Expect the mesoscale convective vortex to continue to slowly move eastward tonight across northern MO/southern Iowa 
producing thunderstorms and rain ahead of the system. Ongoing thunderstorms and rain across southwestern MO are 
airmass thunderstorms and rain and should dissipate shortly after sunset. 


For tomorrow...after the mesoscale convective vortex moves east of the area...some airmass thunderstorms and rain can 
be expected across southern portions of the County Warning Area. Probability of precipitation across the remainder of 
the County Warning Area are mainly to account uncertainties with regard to timing. 


After precipitation moves out of the area...focus changes to the heat 
during the upcoming week. Models forecast deep westerly winds sun with 
850mb temperatures of 22-24c. At this time...have forecast just below mav forecast due to 
some uncertainty of thunderstorms and rain chances. Models suggest northwest flow aloft which may 
allow for a very brief cool down...to lower 90s for Tuesday. 


How long lived these cooler temperatures stay depends on the location of a 
warm front. The GFS and NAM would suggest this fnt pulls northward Monday evening. The 
European model (ecmwf) agrees but brings an mesoscale convective system southward across the County Warning Area Tuesday evening. Have 
little confidence in the models position of this warm front as both the 
GFS and European model (ecmwf) have not been consistent over the past couple of days. 
Therefore...have made only minor changes to the extend forecast due to the 
large uncertainties that far out. 




Tilly 


&& 


Aviation... 
/1230 PM CDT Friday Jul 18 2008/ 
for the 18z tafs... 
primary forecast issue for this taf issuance is location of 
convective development...coverage...and subsequent potential 
impact on any taf sites. Residual mcss from late last night and 
early this morning have produced an outflow boundary situated from 
near Kirk through the Kansas City area. Residual showers persist to 
the northwest of the boundary and into southern Kansas. Don't feel any of 
this activity will impact of any of the taf sites and expect it to 
show a general weakening trend as it moves eastward. Thinking at this time is 
there will be some sort of convective development to the north of 
the boundary tonight across northwest MO as the southwesterly low level jet ramps up and 
this may grow upscale into an mesoscale convective system and impact KUIN overnight. 
Confidence is limited at this time and therefore just included a cumulonimbus group 
after 07z. Elsewhere expecting VFR conditions to prevail although 
clouds will be increasing in the middle-high levels tonight. Any 
chance of convection from kcou to kstl area later tonight into 
Saturday morning will be highly dependent on the southward propagation 
of additional convective outflow which is very difficult to 
resolve this far out. 


Glass 


&& 


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


$$ 


Weather forecast office lsx