Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 201744

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1244 PM CDT TUE SEP 20 2016

Issued at 1033 AM CDT Tue Sep 20 2016

Latest surface analysis is showing a weak boundary extending from
central Illinois through the northern CWA into northern Missouri.
Latest SPC mesoanalysis is showing that atmosphere is becoming
increasing unstable with MUCAPEs of 2000-4000 J/kg across the
area, however it remains capped at this time. There may be some
weak convergence along this boundary this afternoon before it
moves north of the CWA as a warm front this evening. Will
maintain just slight chances of showers and thunderstorms this
afternoon across northeast Missouri and west central Illinois.
Morning soundings still indicate that mixing will be up to around
850mb where temperatures around 20C. This supports going highs
around 90 degrees.



.SHORT TERM...  (Through Late This Afternoon)
Issued at 335 AM CDT Tue Sep 20 2016

Not a lot of changes to the prev forecast for today.

A weak sfc fnt has entered far nrn portions of the CWA early this
morning. This fnt may drift a little further south thru the morning
hours before lifting back nwd out of the area. The main concern with
this fnt is the chance for TSRA. For now, have kept PoPs low as
there is not much guidance suggesting storms developing today.
However, given the presence of the fnt and the warm unstable airmass
in place, believe a threat exists early this afternoon. The threat
shud diminish late this afternoon as the fnt lifts nwd. While the
threat for storms outside this area is not zero, this area is
currently the best chances.

Otherwise, only minor changes in the going temp forecast. Some
guidance suggests going forecast across ern portions of the CWA is
too warm with the sfc ridge struggling to move out of this region.
While this soln is possible, believe the mdls are negatively
impacted by convection that is not likely to occur.


.LONG TERM...  (Tonight through Monday)
Issued at 335 AM CDT Tue Sep 20 2016

Weak frontal boundary to lift north of forecast area tonight, so dry
conditions expected. With mostly clear to partly cloudy skies and
light winds, temperatures to drop into the 60s, especially over the
eastern Ozarks.

Surface ridge to remain anchored over the region through Friday
night. So hot and humid conditions to persist through the end of the
work week. Highs will be in the 85 to 90 degree range each day.

By Saturday, backdoor cold front approaches forecast area from the
northeast but remains rather weak, so should see dry conditions for
Saturday and Saturday night. Therefore, another hot and humid day on
Saturday with highs in the mid to upper 80s.

Main cold front to our northwest begins to move through on Sunday,
so have chances of storms Sunday through Monday. With the
precipitation and cloud cover, temperatures will be near normal by
Monday, with highs in the mid 70s to low 80s.



.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1244 PM CDT Tue Sep 20 2016

Dry and VFR conditions are expected through the period with mainly
light winds. Any thunderstorms that do develop this afternoon will
be too isolated to include in the TAFs at this time.

SPECIFICS FOR KSTL: Dry and VFR conditions with light winds are
expected through the TAF period.





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