Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 252040

340 PM CDT Mon Aug 25 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 320 PM CDT Mon Aug 25 2014

Diurnal convection has once again developed over the higher terrain
of the eastern Ozarks in response to orography and SBCAPE exceeding
3000 j/kg. If these storms exhibit the same trends as those of the
last 5-6 days, they should drift westward and dissipate by sunset.
Otherwise the only other apparent threat of storms should be late
tonight as the cold front currently extending from southeast Iowa
into northwest Missouri slides southeastward into the northern
portion of the CWA. It will remain on the mild-warm side with lows
in the 70s.


.LONG TERM:  (Tuesday through Next Monday)
Issued at 256 PM CDT Mon Aug 25 2014

The exansive upper ridge will remain firm through Tuesday with the
aforementioned surface front oozing only a bit southward from its
position across the northern CWA. Cooler H85 temps and mid level
temps suggest the magnitude of heat will be a tad less than
previous days, however still quite hot and well within advisory
and warning criteria. These cooler temperatures aloft and the
strong heating will contribute to very unstable conditions and
what appears to be a larger region susceptible to diurnal thunderstorms,
enhanced a bit along the front where there is some focus.

Changes in the pattern aloft begin to take place beginning late Tuesday
night-Wednesday as a short wave trof moves along the northern tier
states and across the Great Lakes region into the northeast U.S.
This should give the front some impetus and it is expected to
gradually move southward on Wednesday, with the front anticipated
across southern MO and southern IL by 00z Thursday. Increasing
clouds and a threat of scatttered showers and thunderstorms should
accompany the front along and to its north. Present indications
are cooling aloft and the front should put an end to the magnitude
of heat that we have experienced since late week. That said there
could be a few locations along and south of I-70, especially metro
St. Louis, where highs push into the lower 90s and afternoon heat
index values top 100. These locations would warrant an extension
of advisories or warnings through Wednesday, however given some
uncertainty in the coverage of these heat index values due to more
clouds, the front and convection, I will hold off and let later
shifts get a fresher look.

Eventually as we head into the period from Thursday into the weekend
the impacts of a slow-moving upper trof origination in the western
U.S. will come into play. The models have displayed variability
with the speed and magnitude of this system. It looks like as the
upper trof and associated surface system push into the Plains on
Thursday, it should lead to a northward retreat of our initial
east-west front and then sometime late in the weekend the Plains
system will pass through. In between that time it appears there
will be a prolonged/daily threat of showers and thunderstorms with
highs in the upper 80s to lower 90s.



.AVIATION:  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1224 PM CDT Mon Aug 25 2014

Primarily VFR conditions are expected through the period. The
main exception is light fog overnight due to the humid air mass
over the region. It is possible that an isolated afternoon
thunderstorm could develop and pass over one of the terminals, but
the probability is too low to include thunder in the TAFs at this



MO...HEAT ADVISORY until 8 PM CDT Tuesday FOR Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Knox MO-Lewis MO-Madison MO-Marion MO-Moniteau MO-
     Monroe MO-Montgomery MO-Osage MO-Ralls MO-Reynolds MO-
     Shelby MO-St. Francois MO-Ste. Genevieve MO-Warren MO-
     Washington MO.

     EXCESSIVE HEAT WARNING until 8 PM CDT Tuesday FOR Jefferson MO-
     Lincoln MO-Pike MO-St. Charles MO-St. Louis City MO-St.
     Louis MO.

IL...HEAT ADVISORY until 8 PM CDT Tuesday FOR Adams IL-Brown IL.

     Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-St. Clair IL-Washington IL.



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