Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 182307

607 PM CDT Mon Aug 18 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 250 PM CDT Mon Aug 18 2014

Weak cold front and shortwave expected to bring a chance of
showers and thunderstorms to the area late tonight, especially
across parts of central Missouri and the eastern Ozarks. This is
where the nose of the westerly low level jet will reside.


.LONG TERM: (Tuesday through Next Monday) Issued at 250 PM CDT
Mon Aug 18 2014

Weather story this week will be DANGEROUS HEAT building into the
Greater St. Louis Metropolitan Area. Have decided to issue an
EXCESSIVE HEAT WATCH for Wednesday through Sunday for St. Louis
County, St. Louis City, Madison and St. Clair Counties in
Illinois. Appears temperatures will reach the middle 90s by
Wednesday with heat index readings between 100 and 105 degrees in
the City of St. Louis, with temperatures rising into the upper 90s
for the remainder of the watch period and afternoon and early
evening heat index values around 105 degrees common across the
entire watch area.

Summer pattern will take shape this week as high pressure aloft
builds across the lower and middle Mississippi River valley. The
transition to the pattern will bring chances of showers and
thunderstorms to the region tonight and tomorrow night as the warm
front lifts north across the region. Heat will build across the
region with the hottest temperatures likely occurring Saturday and
Sunday as thermal ridge (+24 to +26C at 850mb) is directly overhead.

The heat should subside by Monday as a cold front moves through the
area and temperatures return to normal.

The chances of precipitation after Tuesday night look very low as
area remains capped under the influence of the upper level ridge.



.AVIATION:  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 531 PM CDT Mon Aug 18 2014

Diurnal cumulus clouds mainly across the St Louis metro area will
dissipate early this evening due to the loss of daytime heating. A
complex of thunderstorms is expected to drop southeastward through
west central and southwest MO late tonight, possibly impacting or
at least grazing COU. There may also be more scattered
showers/storms moving through UIN area late tonight ahead of a
weak surface trough dropping southeastward through northwest MO
and southeast IA. Will include VCSH or VCTS in the UIN and COU
tafs late tonight/early Tuesday morning. Should be mid-high level
warm air advection cloudiness along with convective debris
cloudiness late tonight/Tuesday morning. Should also be scattered
diurnal cumulus clouds again late Tuesday morning and afternoon.
Mainly a light sly surface wind tonight, then gradually strengthening
on Tuesday and veering around to a w-swly direction by late Tuesday
afternoon. There may be some patchy light fog late tonight, mainly
in SUS and CPS.

Specifics for KSTL: Few-sct diurnal cumulus clouds will dissipate
early this evening, with mid-high level clouds late tonight and
Tuesday morning. Weakening convection may impact STL Tuesday
morning, but will leave the STL taf dry for now as the better
chance of showers/storms should be north and west of STL late
tonight and west-southwest of STL Tuesday morning. Scattered
diurnal cumulus clouds should develop again late Tuesday morning
and afternoon. Light sly surface winds tonight, then veering
around to a swly direction Tuesday and increasing to about 12 kts
Tuesday afternoon.



MO...EXCESSIVE HEAT WATCH from Wednesday afternoon through Sunday
     evening FOR St. Louis City MO-St. Louis MO.

IL...EXCESSIVE HEAT WATCH from Wednesday afternoon through Sunday
     evening FOR Madison IL-St. Clair IL.



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