Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 191904
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
204 PM CDT TUE JUL 19 2016

.UPDATE...
Issued at 154 PM CDT Tue Jul 19 2016

Have updated PoPs again, main focus now is moving up timing of
cluster of storms across IA. Latest timing suggests line of storms
will move into nrn portions of the CWA between 21z and 22z. These
storms are expected to continue to travel sewd, likely along the
ern edge of the sfc boundary across the region, which is still
roughly along a line from KIRK to KSTL to KENL.

The main question is if this line will be severe. Until now, the
line has struggled to generate strong wind gusts at the sfc.
However, this same area has been relatively worked over by earlier
convection. Believe the strength of these storms will increase as
they continue to drop further SE, into an area of higher CAPE and
little if any CIN. These storms will continue to be monitored for
severe potential, but a watch may be needed soon.

Issued at 1233 PM CDT Tue Jul 19 2016

Have increased PoPs thru this evening to account for latest radar
trends, both along the Mississippi River and for the cluster of
storms across IA to drop swd late this afternoon and into the
evening. Given the high level of CAPE available and little CAP,
any of these storms may be severe despite the low shear. Best
focus for storms will be along a sfc boundary currently from
roughly KIRK to KSTL to near KENL thru this afternoon. Line of
storms over IA shud continue sewd reaching nrn portions of the CWA
late this afternoon. More questions remain how far south this
convection will propagate before dissipating and have gradually
reduced PoPs mid thru late evening.

Tilly

&&

.SHORT TERM...  (Through Late This Afternoon)
Issued at 345 AM CDT Tue Jul 19 2016

Main concern for today and through the end of the week continues to
be the heat.

Will start out the day mostly sunny, though debris cloudiness from
MCS currently over Nebraska will eventually move into the area later
this morning and this afternoon.  While this will likely cut down on
some of the solar insolation later this morning and this evening,
forecast soundings are showing mixing up to 750mb which favors the
warmer GFS MOS highs in the mid 90s in most areas.  Frontal boundary
will move south into the area today which will cause dewpoints to
pool along it.  Values are expected to rise into the mid 70s, so in
combination with the heat, expect heat index values to reach the 100-
107 degree range this afternoon and this evening.  Lows tonight will
only fall into the 70s, with around 80 in the St. Louis heat island.

Do expect another day with isolated thunderstorms as the
aforementioned cold front currently just north of the area will move
south, becoming oriented northwest-southeast near the Mississippi
River by early afternoon according to the latest runs of the RAP.
MLCAPES are forecast to reach 1500-2000+ J/kg by this afternoon with
relatively weak deep layer shear.   Forecast soundings are showing
some inverted-V soundings, so can`t rule out a few storms with some
strong wind gusts.  Rain chances tonight are less certain as the
CAMS are showing different solutions on how long thunderstorms will
last into the evening.  For now will just keep a slight chance of
far northeast Missouri and west central Illinois for early this
evening until the forecast become more clear.

Britt

.LONG TERM...  (Tonight through Monday)
Issued at 345 AM CDT Tue Jul 19 2016

Heat headlines look like they`re in good shape through the end of
the week. The center of the upper level ridge will sit over Oklahoma
at least through Friday before it begins to weaken slightly.  This
will lock the excessive heat and humidity in over the region. Latest
heat index forecast differs little from previous with 100+ across
the entire area at least through Friday. Unfortunately it looks
like there will be little if any relief in the way of afternoon
thunderstorms. GFS forecast soundings show a degree or two of cap
each day with plenty of synoptic scale subsidence due to the upper
ridge. Without a boundary to help force convection through the
cap, Think there`s really only a slight chance of thunderstorms on
any day Wednesday through Friday. Medium range guidance has slowed
the weakening of the ridge and the advancing cold front from the
north. Consequentially, Saturday looks hotter than previously
forecast, and may be just as hot as Thursday and Friday. Speaking
of Thursday and Friday...both GFS and ECMWF MOS guidance is
showing temperatures between 96 and 100 across the region both
days...and I see no reason not to believe it. In fact, both models
are showing the same highs for Saturday too. This may necessitate
an expansion of the excessive heat warning both in areal coverage
and in time through Saturday if the models hold on to this
forecast. Since this is the first run that I`ve seen with this
slowing trend, I will hold the headlines as they are and wait to
see if if subsequent runs come in consistently slower.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1233 PM CDT Tue Jul 19 2016

TSRA forming along sfc convergence along the MS River. This will
provide a focus for TSRA thru the afternoon. TSRA across IA are
expected to drop sewd this afternoon impacting KUIN late this
afternoon into the evening. This cluster of storms may drop as far
south as KSTL/KSUS/KCPS, but have left out of the TAF for now due
to uncertainty. Otherwise, light and vrb winds and VFR outside of
any storms.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT Friday for Audrain MO-Callaway MO-
     Crawford MO-Franklin MO-Gasconade MO-Iron MO-Knox MO-Lewis
     MO-Lincoln MO-Madison MO-Marion 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 7 PM CDT Friday for Boone MO-Cole
     MO-Jefferson MO-Moniteau MO-Saint Charles MO-Saint Louis
     City MO-Saint Louis MO.

IL...Heat Advisory until 7 PM CDT Friday 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 7 PM CDT Friday for Madison IL-
     Monroe IL-Saint Clair IL.

&&

$$

WFO LSX



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