Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200857

Area Forecast Discussion
National Weather Service Saint Louis MO
357 AM CDT WED JUL 20 2016

.SHORT TERM...  (Through Late This Afternoon)
Issued at 355 AM CDT Wed Jul 20 2016

Main concern continues to be the extended heat wave.  Area still is
under extensive area of cloudiness behind MCS that has already moved
well off to the east early this morning.  These clouds will
gradually thin later this morning and this afternoon allowing for
heating later this morning and this afternoon.  RAP/GFS forecast
soundings show mixing up to 850mb which supports highs in the lower-
mid 90s once again today. Dewpoints will rise back up into the lower-
mid 70s later today as moisture has been added to the atmosphere by
the rain that fell from the MCS that moved through the area
yesterday. This will result in heat index readings this afternoon in
the 100 to 106 degree range.

Radar is showing some recent development of showers and
thunderstorms over southwest Illinois.  This is an area of low level
moisture convergence on the nose of the low level jet. Latest runs
of the RAP show this moisture convergence lasting into mid morning
hours across eastern Missouri and southwest Illinois before shifting
off to the east, so will keep a chance of thunderstorms going in the
forecast.  RAP is also showing a weak boundary over the western CWA
that the HRRR shows additional thunderstorms developing along later
this morning into the afternoon hours.  This boundary will lift
northeast of the area by this evening, so will keep the dry forecast
after 00Z.


.LONG TERM...  (Tonight through Tuesday)
Issued at 355 AM CDT Wed Jul 20 2016

Hot and humid weather will continue across the region for Thursday
at least through Saturday...and probably into Sunday as well. All
guidance now shows the upper level ridge staying in place on
Saturday, and the shortwave which is advertised to move through the
Midwest is delayed until late Sunday.  Heat index values have maxed
out at 105 plus across almost the entire area for 2 out of the last
3 days, and Thursday through Saturday look like they will be at
least as hot if not hotter.  Since this will be at least 5 out of at
least a 7 day period with heat index values of 105 or greater, have
expanded the heat warning to encompass the entire area. Not too keen
yet on extending the heat headlines into Sunday due to the decent
chance for afternoon precip. Both the ECMWF and GFS are printing out
a broad area of relatively light QPF Sunday with some weak to
moderate low level moisture convergence ahead of the trof. This
suggests scattered thunderstorms across the area which may suppress
high temperatures.  That being said, if guidance continues to slow
the progression of this weekend`s shortwave the warning will need to
be extended into Sunday.

Medium range guidance has the front stalling over southern Missouri
on Monday.  Temperatures north of the front should 5 to 10 degrees
cooler...which just means that highs will be closer to normal in the
upper 80s and lower 90s.  It should feel less humid though with
dewpoint temperatures dropping to 65 to 70.  Both the ECMWF and the
GFS keep he front south of the area through Tuesday.  The GFS is
much wetter than the EC over southern Missouri.  Don`t have a strong
feeling either way so stuck close to ensemble guidance which has low
chance/slight chance across southern zones both Monday and Tuesday.



.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1152 PM CDT Tue Jul 19 2016

VFR conditions are expected to prevail at the TAF sites thru the
valid period. There is increasing concern that there will be some
VSBY reductions in mist just before sunrise thanks to the wet
ground at most sites and what should be clearing skies and already
low dewpoint depressions. Have added in TEMPO groups for this at
most sites, save KSTL. Otherwise, surface winds will become more
due southerly heading into the day on Wednesday and continuing
into Wednesday night.



Saint Louis     95  81  97  80 /  20  10   5  10
Quincy          93  75  96  76 /  20  10   5  10
Columbia        95  75  96  75 /  20  10  10  10
Jefferson City  96  75  98  76 /  20  10  10   5
Salem           92  74  94  76 /  20  10  10  10
Farmington      93  73  93  75 /  20  10  10  10


MO...Excessive Heat Warning until 7 PM CDT Saturday 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 7 PM CDT Saturday 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



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