Area Forecast Discussion
Issued by NWS St. Louis, MO

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723
FXUS63 KLSX 221800
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
100 PM CDT FRI JUL 22 2016

.UPDATE...
Issued at 1253 PM CDT Fri Jul 22 2016

The complex of showers and storms this morning put a lid on
heating and much of the CWA remained in the 70s with rather
stable air at midday. Clouds should thin and winds will recover
in the wake of the outflow and this should allow temps to warm,
and this trend is already evident in the 18z obs. Greatest heat
will be evident during the late afternoon from 21-23z. Given the
slow start the highs are not expected to be as hot as earlier
advertised. Peak heat index values late this afternoon will depend
largely on the temperature and dew point recovery, and the thinking
at this time they may be be closer to the 100-105 range. No
changes to the ongoing heat headlines.

Glass

&&

.SHORT TERM... (Through Sunday)
Issued at 353 AM CDT Fri Jul 22 2016

A thunderstorm complex developed last night over WI and progressed
into northern IL before turning SWWD. Despite strong capping
noted at 700mb, the thunderstorm complex moved through central IL
overnight and reached the LSX CWA early this morning. The complex
should eventually dissipate this morning, although its outflow
boundary may provide a focus for additional thunderstorm
development this aftn.

The primary forecast concern remains the ongoing heat/humidity
across the region. No changes to the existing headlines are
planned. Hot/humid conditions are still expected to persist
through Sunday until a cold front moves into the region. Similar
to the last several days, isolated to scattered thunderstorms are
possible during the afternoon and evening hours, and there may be
another overnight thunderstorm complex before the heat wave
finally ends.

The combination of daytime high temperatures in the mid to upper
90s along with dew points in the 70s will yield heat index values
above 105 deg F across the area each day through Sunday. Little
relief from the oppressive heat is expected at night. Overnight
lows will remain in the mid to upper 70s (closer to 80 in the
urban core of the St. Louis metro area), and temperatures will be
slow to fall during the evening hours. Case in point: the hourly
air temperature at KSTL was still 90 deg F at 11pm last night.

It is very unusual in this area for the air temperature to reach
100 deg F when such high dew points are present, but the century
mark appears to be within reach both today and tomorrow. The
concern for today is whether mid/high clouds from the decaying
early morning thunderstorm complex will dissipate quickly enough
to allow full daytime heating.

Kanofsky

.LONG TERM... (Sunday Night through Thursday)
Issued at 353 AM CDT Fri Jul 22 2016

Early morning water vapor imagery depicted a shortwave located over
the PacNW. This feature will continue moving eastward over the next
few days, eventually breaking down the upper ridge and sending a
cold front towards the MO/IA border on Sunday night. The interaction
between a LLJ and the slow-moving cold front should produce an area
of thunderstorms near and ahead of the front on Sunday night into
Monday.

Models are split on whether the aforementioned cold front moves
through MO or whether it stalls across MO. The location of the
front is important for determining pcpn chcs next week when
several disturbances move across the region within the quasizonal
to weakly NWLY flow aloft. SChc/Chc PoPs look reasonable attm
given the amount of uncertainty.

Kanofsky

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1237 PM CDT Fri Jul 22 2016

The complex of showers and thunderstorms this morning has all but
dissipated, and has pushed an outflow boundary well to the south.
Stable air prevailed in its wake, and this suggests that the
threat of additional showers and storms at any of the terminals
this afternoon and early evening is rather remote. VFR flight
conditions should prevail through at least evening. The overnight
forecast is a little more tricky. If we don`t get good heating and
breaks in the clouds this afternoon there could be some fog
concerns. Will also have to keep an eye on any thunderstorm
complexes dropping south late tonight out of IA. If this should
occur then KUIN would have the greatest threat of showers and
storms, however confidence is quite low and therefore nothing has
been mentioned in the TAF.

Specifics for KSTL:

VFR flight conditions are expected throught the forecast period.
The complex of showers and thunderstorms this morning has pushed
an outflow boundary well to the south with stable air currently
dominating. While destabilization is expected with heating this
afternoon, the threat of additional showers and storms at KSTL
this afternoon and evening is rather remote.

Glass

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Excessive Heat Warning until 8 PM CDT Sunday for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln
     MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Shelby MO-Warren MO-Washington MO.

IL...Excessive Heat Warning until 8 PM CDT Sunday for Adams IL-Bond
     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-Saint Clair IL-Washington
     IL.

&&

$$

WFO LSX



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