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Area forecast discussion...updated aviation 
National Weather Service St Louis MO
547 am CDT Sat Jul 26 2014

Short term: (today and tonight)
issued at 330 am CDT Sat Jul 26 2014

Two major concerns over the next 24 hours are heat today and the
thunderstorm/severe threat this afternoon and tonight. The new
model runs continue to show a very favorable pattern for hot
temperatures today with a prominent low level thermal ridge in
place featuring 850 mb temperatures greater than +24 degc this
afternoon and veering southwest-westerly lower trop flow. This
should yield high temperatures well into the 90s with the I-70
corridor in line for 95-100. These values agree well with upstream
conditions yesterday. As dicussed in the previous afd, mixing will
result in a dew point min from the Eastern Ozarks into portions of
central MO, with the highest dew points displaced north and east of
the hottest ambient air temperatures. The best overlap and highest
heat indices near 105 degrees will be within Metro St. Louis and
a few counties west and east, and I have expanded the heat
advisory this afternoon to account for the slight greater areal

Now for the thunderstorm and severe weather threat. There could be
a few spotty showers or thunderstorms through mid morning roughly
along an axis from Bourbon to St. Louis to Vandalia where the
westerly low level jet is producing some moisture convergence and there has
been an increase in cloud cover in the last hour or so. Otherwise
the main threat for storms and severe weather looks to be from
around mid-afternoon through this evening. I'm still not exactly
sure how this is going to unfold. The synoptic scale front should
be located across northern MO and central Illinois and the airmass along
and south of the front will be very unstable and initially capped
owing to warm mid level temperatures. The cap removal is the
largest unknown and could occur via a number of mechanisms - an
eastward moving mesoscale convective vortex remnant from the weakening mesoscale convective system over KS, the
leading edge of height falls/cooling aloft associated with the
southeast moving Saskatchewan upper low/trof, cooling associated
with mid level convection which could form above the eml over
northern MO. The concensus of most of the guidance is that robust
storm development will occur across northern MO into central Illinois
after 20-21z within the frontal zone. Unseasonably strong deep
layer shear and the high instability favor organized severe. The
overall pattern and shear/strenghening flow aloft are suggestive
of upscale growth from the late afternoon and evening into a forward
propagating mesoscale convective system moving into the Ohio Valley with a high damaging
wind threat. The Storm Prediction Center moderate risk area has the zone of greatest
probability well delineated at this time.


Long term: (sunday through friday)
issued at 330 am CDT Sat Jul 26 2014

The cold front will extend from northeast Illinois to around St.
Louis into northern Oklahoma at 12z and should exit the County Warning Area by
early afternoon as the upper low/trof moves southeastward into the
Great Lakes. The precipitation threat will be considerably lower
Sunday morning ahead of the front and I don't expect to see much.
Increasing northwesterly winds will usher drier and cooler air
into the region during the afternoon in the wake of the front. The
large surface high will settle into the nation's midsection on
Monday and then become a dominant feature into midweek as a deep
upper trof persists over eastern noam. Below average temperatures
will prevail throughout next week.



Aviation: (for the 12z tafs through 12z Sunday morning)
issued at 534 am CDT Sat Jul 26 2014

VFR conditions expected at all taf sites through around 20z
today...but thunderstorms should form shortly thereafter and
primarily threaten KUIN. Given the uncertainty of coverage, will
include a vicinity thunder remark for now. Farther south over the Metro
taf sites, the threat looks to be less so will keep dry for now.
Cold front and wind shift will approach taf sites around 12z.

Specifics for kstl: VFR conditions expected through this taf
period, however there is a slight chance for thunderstorms this
afternoon into this evening. Most activity should remain NE of
kstl, but will have to monitor closely, particularly after around
21z. Southwest winds will become northwest as a cold front passes
around 12z Sunday.



Lsx watches/warnings/advisories:
MO...heat advisory from 1 PM this afternoon to 7 PM CDT this evening
for Franklin MO-Jefferson MO-St. Charles MO-St. Louis city
MO-St. Louis MO-Warren MO.

Illinois...heat advisory from 1 PM this afternoon to 7 PM CDT this evening
for Clinton Illinois-Madison Illinois-Monroe IL-St. Clair Illinois-Washington



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