Area Forecast Discussion
Issued by NWS St. Louis, MO

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419
FXUS63 KLSX 281959
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
259 PM CDT THU JUL 28 2016

.SHORT TERM... (Through Friday)
Issued at 257 PM CDT Thu Jul 28 2016

(Tonight)

Three items are the principle focusing mechanisms for convection
this afternoon. The first is the main cold front now located
southeast of STL metro, draped from southern IL thru southeast MO.
The second is an upper level disturbance located over STL metro.
The third is a weaker, secondary TROF located from northwest IL
thru northeast MO. With a weakly sheared, moderately unstable
environment with little-no CINH, showers and storms are popping up
all over, but mainly in those three areas.

Convection is being greatly enhanced with diurnal influences and
should lessen with loss of heating early this evening and into the
overnight, with an overall trend towards areas south of I-70 as it
does so.  Many areas should be dry overnight, with models now taking
a MCS track well to the west.

Generally favored the higher min temps on the MET MOS, yielding
upper 60s to around 70.

(Friday)

While MCS should miss our area to the west, it appears the secondary
TROF should be in the southern CWA once diurnal influences kick into
gear again, and it is in this area where the highest PoPs will be,
beginning just before midday and continuing thru the afternoon
hours. Lesser chances for showers and storms will exist elsewhere.
Otherwise, look for max temps to be a few degrees less than
persistence, thanks to cooler air filtering in behind that secondary
TROF.

TES

.LONG TERM... (Friday night through Next Thursday)
Issued at 257 PM CDT Thu Jul 28 2016

(This Weekend)

NAM and GFS are still showing west northwesterly flow setting up
over the area this weekend with a series of weak vort maxes that
will move southeast through it.  There will still be a wavy frontal
boundary beneath this upper flow that will continue to act as a
focus for scattered thunderstorm development, particularly during
the daytime when instability will be maximized and CINH will be the
lowest.

Temperatures over the weekend will stay in the 80s, with 850mb
temperatures in the 15-18C range.


(Monday through Thursday)

Forecast for next week is not as clear as it was yesterday as global
models are not as in as good agreement. It still looks like the
upper trough will move east and off the East Coast by early-mid
week.  This will keep a stalled front over the region into Tuesday
keeping showers and thunderstorms in the forecast.  However, the GFS
and ECMWF now differ on how strong the upper high will build into
Midwest by the middle of next week. The GFS is more robust next week
in building the upper ridge over the area on Wednesday and Thursday.
Still expect temperatures will warm up quickly next week though once
the upper trough moves to the east of the area as 850mb temperatures
warm into the lower 20sC.


Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1235 PM CDT Thu Jul 28 2016

VFR conditions and light NW surface winds are expected to prevail
at the TAF sites for much of the valid period. There is potential
for VSBY reductions in mist once again tonight, and depending on
exactly how the specifics play out, could lead to some IFR VSBYs
in spots. For now, have added MVFR VSBYs into most TAFs, save STL
for being a bit warmer, and COU because of anticipated additional
clouds reaching them earlier overnight. Rain chances continue to
look enough to warrant mention for all sites this afternoon,
with the better chances shifting off to the south and east late
this afternoon and into tonight, as both the upper level
disturbance and surface cold front should both be at least there
by that time. Rain chances look much more uncertain heading into
late tonight and Friday, with latest model trends showing that the
late tonight-early Friday event may be more deflected to the south
of our area. Prefer to leave out of TAFs given event today and
this new uncertainty on Friday.

TES

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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