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Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
637 am CDT Sat Oct 11 2008 


Discussion... 
/355 am CDT Sat Oct 11 2008/ 


Models remain in good agreement on mass fields until Monday but 
then show some noticeable differences thereafter. Models continue 
to show southwesterly middle level flow to dominate our region until early 
next week...when the deep low over the central rockies lifts northeastward and 
passes through the northern plains and upper MS valley. This will then 
result in a pattern shift...with a more zonal flow setting up for 
much of next week. At the surface...southeast to S flow will persist until 
Monday maintaining the much above normal temperatures. Models have 
maintained their slower trend on the frontal passage...which makes sense 
considering the southwesterly middle level flow until passage of the strong 
ejecting rockies system Monday night into Tuesday...which will 
steer the middle level flow westerly enough to result in a more realistic 
frontal passage through the forecast area during this time. NAM seems to be the outlier 
here and has a faster southeastward frontal propagation...and this solution has 
been discarded. 


Dry weather is largely expected through Monday afternoon...although 
moisture will steadily be on the increase...with dewpoints 
expected to exceed 60f by this afternoon...and precipitable waters  near 200pct 
of normal by Sunday. This may allow development of airmass type 
convective rain showers/thunderstorms and rain during both Sunday and Monday afternoon...but focus 
hard to pin down...and soundings show pretty shallow convection at 
that...should it form. 


With approach of cold front and its eventual passage...have confined 
the rain chances to Monday night through Wednesday...although there 
is model dissension on whether or not to eject the final piece of 
energy from the deep trough currently over the western Continental U.S....which 
will result in maintain some sort of rain chance through Wednesday. Slug 
of tropical moisture from Norbert in the eastern Pacific looks like it 
will be quick to surge northward...reaching the Central Plains by Sunday 
and not stopping there...pushing further northeastward and becoming absorbed 
into ejecting strong northern stream system early next week. Moisture 
increase over the forecast area will be substantial nevertheless...but not to 
the degree that this tropical moisture would have it. Instability 
looks downright meager...with both NAM and GFS showing MUCAPES 
struggling to exceed 100 j/kg and frequently near zero...with cape 
areas on soundings quite shallow. Maintained a minimal thunder 
slight chance for daytime hours of Monday and Tuesday. 


Otherwise...warm temperatures will be the story through Monday. Mixing 
heights once again expected to be between h900-h875 the next few 
days. With little cloud cover diff and h900 temperatures rising by 
1-2c this afternoon...look for 2-4f higher maximum temperatures than persistence. 
H900 temperatures will then either maintain these levels or slip by 1c or 
so...but added item will be increased daytime cloud cover...which 
should result in temperatures at or slightly below their eventual peaks 
today. Either way...maximum temperatures to be around 10f above normal each 
day through Monday. 


Tes 


&& 


Aviation... 
/632 am CDT Sat Oct 11 2008/ 
for the 12z tafs... 
primary concern for aviators this morning is patchy IFR/LIFR fog 
in river valleys. Some more widespread marginal visibilities across parts 
of eastern Missouri. All this fog should dissipate between 13z and 
14z this morning. Scattered cumulus at 3500-4000ft and light southeast 
flow will prevail for the rest of the day. 


Carney 


&& 


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


$$ 


Weather forecast office lsx