Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232331
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
631 PM CDT Sun Jul 23 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 350 PM CDT Sun Jul 23 2017

Isolated to scattered thunderstorms have developed near a cold front
which is slowly sinking southward through Missouri and Illinois.
Convection will likely continue through the evening hours before
dissipating with the loss of diurnal heating. There is much less
instability and there are far less favorable lapse rates this
afternoon compared to yesterday afternoon, and both the air
temperature and the dew point will be decreasing overnight behind
the front. Although an isolated strong to severe storm is possible,
a repeat of last night`s severe weather is not anticipated.

Heat index values were hovering near the century mark this
afternoon, therefore the Excessive Heat Warning will be retained
through the early evening with the expectation that it will be
cancelled or allowed to expire this evening. Overnight lows will
likely fall into the 60s areawide (closer to 70 in the urban core of
St. Louis). Highs tomorrow will be 5-10 degrees cooler across the
area except over the eastern Ozarks where temperatures will likely
be similar to what they were today.

42

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 350 PM CDT Sun Jul 23 2017

Main focus will be temps on Wed with a relatively uneventful week
ahead.

Mdls are in fairly good agreement thru the period. Period begins
with weak NW flow aloft and a sfc ridge building into the region
from the Great Lakes. Light ely flow and a mostly clear sky shud
allow for ample radiational cooling and have trended aob the cooler
guidance.

With sfc winds becoming more sly on Tues and the upper ridge
building into the area, temps shud warm up quickly. The main warm up
is still expected to be Wed. The GFS suggests convection possible as
early as mid morning thru central portions of the CWA on the ern
fringes of the cap with good low level support. While this can not
be ruled out, does not seem the most likely soln attm. Have
therefore continued temps in the mid to upper 90s due to 850mb temps
around 22C.

A cdfnt shud push thru the CWA Thurs and Fri bringing TSRA with it.
Given amount of CAPE that shud be available ahead of the fnt, a
severe threat shud exist on Thurs and possibly Fri. However, weak
deep layer shear will help keep threat limited. With K-index values
around 40C, will need to monitor this event for heavy rain
potential.

A large sfc ridge builds into the region behind the cdfnt with NW
flow aloft. Much cooler conditions currently expected with 850mb
temps in the 12C to 14C range.


Tilly

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 600 PM CDT Sun Jul 23 2017

Scattered thunderstorms have developed across west central Illinois
late this afternoon. These storms are expected to last a couple more
hours before dissipating early this evening. A few storms may
still move down into the St. Louis area early this evening,
however coverage is expected to be too low to include in any of
the TAFs at this time. Otherwise dry and VFR conditions are
expected through the TAF period. Light winds are expected to veer
out the north.

SPECIFICS FOR KSTL:

Isolated thunderstorms over west central Illinois are expected to
slowly dissipate by early this evening. While there is some small
chance for these storms to move into the St. Louis area early this
evening, coverage is not expected to be great enough to warrant a
mention of TS in the TAF at this time.  Otherwise dry and VFR
conditions are expected through the TAF period. Light winds are
expected to veer to the the north.

Britt

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     71  90  71  92 /  20   0   0   5
Quincy          65  84  66  88 /  10   0   0   0
Columbia        68  87  67  90 /  10   0   0   0
Jefferson City  70  90  68  92 /  10   0   0   5
Salem           69  88  66  88 /  20   0   5   5
Farmington      70  90  68  90 /  10   5   5  10

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Excessive Heat Warning until 8 PM CDT this evening for Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Reynolds MO-Saint Charles MO-Saint
     Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

IL...Excessive Heat Warning until 8 PM CDT this evening for Madison
     IL-Monroe IL-Saint Clair IL.

&&

$$

WFO LSX



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