Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 222034

Area Forecast Discussion
National Weather Service Saint Louis MO
334 PM CDT Sat Jul 22 2017

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 334 PM CDT Sat Jul 22 2017

Oppressively hot and humid conditions were noted across the region
early this afternoon, and several ASOS sites had already passed the
century mark by 18-19z. At 20z, KSTL reported a temperature of 104
degrees with a dew point of 69 degrees, yielding a heat index of 111

A boundary was located near the MO/IA border as per regional METARs
and satellite imagery. A shortwave moving along the US/Canada border
towards the Great Lakes will push this boundary southward as a cold
front into MO/IL. Isolated to scattered thunderstorms are expected
to develop near this boundary within an unstable air mass. A few
storms could be strong to severe given steep H7-H5 lapse rates and a
very unstable air mass. A separate area to monitor for potential
SHRA/TSRA development late this afternoon and this evening will be
along a remnant outflow boundary which moved across the region
earlier this morning.

Although the cold front will move through the region tonight, there
won`t be much change in the air mass characteristics until tomorrow
night when a second cold front moves through the region (see
discussion below). Highs will be around 5-7 degrees cooler on Sunday
compared to today, which will translate to peak heat index values of
100-105 rather than 110+ across the southern half of the CWA.
Although the heat will be slightly less intense on Sunday, it still
appears dangerous enough to keep the existing heat headlines in


.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 334 PM CDT Sat Jul 22 2017

Not a lot of changes from the prev forecast. A cooler cdfnt is progd
to push into the CWA Sun evening with sct TSRA possible near the

Unfortunately, the cooler temps will be short lived as the thermal
ridge begins to build into the region with height rises by Tues.
Still, with a somewhat nly and ely sfc flow, have trended slightly
cooler. Regardless, the dewpoints shud still be much cooler allowing
temps to drop into the 60s at night.

The upper ridge continues to build into the area on Tues and Wed
with 850mb temps in the 21C to 24C range by Wed. This shud result in
temps in the upper 90s to near the century mark for the St. Louis
metro area. This heat event shud be short lived with a deep upper
trof and associated sfc cdfnt pushing thru the area Wed night and
Thurs. Depending on the progress of the fnt, temps on Thurs may not
be warm enuf across srn portions of the CWA. Behind this fnt, much
cooler and drier air returns on Fri into next weekend with a 1016 mb
sfc ridge, 850mb temps around 15C and NW flow aloft.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1202 PM CDT Sat Jul 22 2017

SPECIFICS FOR KUIN: An outflow boundary was still affecting the
prevailing wind direction at KUIN at TAF issuance, but winds
should continue to veer this afternoon and become southwesterly to
west-southwesterly during the first 6-8 hours. Isolated to
scattered SHRA/TSRA are expected to develop late this afternoon
near a weak front, but KUIN may be too far north of the boundary
to experience much precipitation. Winds will become northwesterly
after fropa.

SPECIFICS FOR KCOU: Scattered SHRA/TSRA are expected to develop
late this afternoon and early this evening invof a weak front as
it sinks southward through the region. Winds will become
northwesterly after fropa.

SPECIFICS FOR KSTL, KSUS, KCPS: An outflow boundary moved through
the St. Louis metro area terminals a few hours ago, which shifted
the winds to 030-060. Winds have been slowly veering in the wake
of the boundary and were 130-160 at TAF issuance. Based on
upstream observations, winds will continue to slowly veer over the
next few hours before returning to the prevailing southwesterly
or west-southwesterly flow. Scattered SHRA/TSRA are then expected
to develop this evening invof a front as it slowly sinks
southward through the region. Winds will become northwesterly
after fropa.



Saint Louis     80  97  72  91 /  30  20  20   0
Quincy          74  92  66  85 /  30  10  20   5
Columbia        74  93  68  88 /  40  20  10   0
Jefferson City  75  94  69  90 /  40  20  10   5
Salem           77  94  70  88 /  30  10  10   5
Farmington      76  94  69  90 /  30  30  20  10


MO...Excessive Heat Warning until 8 PM CDT Sunday 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.

     Excessive Heat Warning until 8 PM CDT this evening for Audrain
     MO-Knox MO-Lewis MO-Marion MO-Monroe MO-Pike MO-Ralls MO-
     Shelby MO.

IL...Excessive Heat Warning until 8 PM CDT Sunday for Bond IL-Calhoun
     IL-Clinton IL-Jersey IL-Madison IL-Marion IL-Monroe IL-
     Randolph IL-Saint Clair IL-Washington IL.

     Excessive Heat Warning until 8 PM CDT this evening for Adams IL-
     Brown IL-Fayette IL-Greene IL-Macoupin IL-Montgomery IL-
     Pike IL.



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