Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 172025

Area Forecast Discussion
National Weather Service Saint Louis MO
325 PM CDT Sun Jun 17 2018

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 323 PM CDT Sun Jun 17 2018


A few isolated showers and thunderstorms are expected to quickly
wane early this evening with loss of instability. Rest of the night
should be very much like that of last night with very mild
conditions under a mostly clear sky expected. Low temperatures are
forecast to be in the mid 70s to near 80 degrees tonight,
threatening record high minimums for the date.


Main story will continue to be very hot and humid weather conditions
as they are expected to last at least through the day on Monday.
Going heat headlines still look good for Monday as combination of
high temperatures in the mid 90s along with dewpoints mainly in the
low 70s creates peak head index values of 100-105F for most

Dry conditions are favored on Monday as mid/upper level ridge
continues to dominate the mid-Mississippi Valley. What is different
on Monday than that of the past couple of days is some more capping
aloft between 700 and 800 hPa. The thought is that the introduction
of this weak capping inversion should prevent the formation of even
isolated diurnal shower/thunderstorm activity.


.LONG TERM...  (Monday Night through Next Sunday)
Issued at 323 PM CDT Sun Jun 17 2018

(Monday Night - Next Sunday)

Mid/upper level ridge axis which has been the dominant weather
feature the past few days will begin to slwoly break down early this
upcoming week. A cold front looks to come down southward into IA/IL
on Monday night as a sfc low transverse southeastern Canada. This
frontal boundary will be the main focus for convection through much
of the remainder of the forecast period. Latitudinal postion of this
front looks like it will be highly tied antecedant thunderstorm
activity. Two weak surface lows are expected to develop across the
south-central Plains and move the front northward as a warm front
but ongoing convection will try to keep it at bay if not push the
boundary further to the south. Active weather with rounds of showers
and thunderstorms is becoming increasingly likely in the Tuesday
night through Saturday time frame. Latest NWP guidance suggests
front may (for at least a brief time) clear the CWA to the south
sometime next weekend as a surface low moves through the Great Lakes.

Temperatures on Tuesday will start off well above normal and quite
humid, but still a lot of uncertainty with respect to cloud cover
and potential for thunderstorms. For these reasons, continued to
hold off on the extension of any heat headlines, but there still is
a possibility that headlines will be needed one last day on Tuesday.
High temperatures should cool off back to near normal for Wednesday
through Saturday due to the front wavering nearby bringing copious
amounts of cloud cover and chances for thunderstorms. Nighttime lows
should be still on the mild side however for these same reasons.



.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1224 PM CDT Sun Jun 17 2018

Isolated thunderstorms are once again the primary concern during
the afternoon/early evening hours but low coverage precludes
mention in the TAFs. Outside of any thunderstorm activity, dry/VFR
conditions are likely with a south/southwest wind prevailing.


Will have to keep an eye on isolated thunderstorms developing this
afternoon. Low coverage of storms prevents any mention in the
going TAF but the possibility of storms affecting the terminal
does exist through very early this evening. Mostly clear sky with
light south winds expected tonight with diurnal cumulus forming
again on Monday along with a south/southwest breeze.




Record Highs and Warmest Lows


STL 100 (1953) 79 (2009)

COU 100 (1953) 75 (2014)

UIN 99 (1913) 77 (1944)


MO...Heat Advisory until 8 PM CDT Monday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron 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 Francois MO-Sainte Genevieve MO-Shelby
     MO-Warren MO-Washington MO.

     Excessive Heat Warning until 8 PM CDT Monday for Jefferson MO-
     Saint Charles MO-Saint Louis City MO-Saint Louis MO.

IL...Heat Advisory until 8 PM CDT Monday for Adams IL-Bond IL-Brown
     IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Marion IL-Montgomery IL-Pike IL-Randolph IL-
     Washington IL.

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



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