Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 170635

135 AM CDT Wed Sep 17 2014

Issued at 129 AM CDT Wed Sep 17 2014

Based on latest vsby trends of surface obs as well as HRRR and
lamp guidance will be going out with a dense fog advisory for our
eastern counties shortly...until 10am. It`s possible we may need
to expand a bit west and north in a few hours, and will at least
mention patchy fog as far west as eastern MO. However, upstream
clouds heading our direction should limit threat of widespread
dense fog, especially west of the Mississippi River.



.SHORT TERM:  (Through Tonight)
Issued at 230 PM CDT Tue Sep 16 2014

A weak s/w will approach the CWA late tonight bringing a chance
for storms to wrn and srn portions of the CWA late tonight.
Otherwise, expect clouds to continue to break up during the
afternoon and into the evening. Clouds are expected to build into
the region from the W tonight ahead of the s/w. Have trended twd
a compromise of guidance for wrn portions of the CWA and twd the
cooler guidance for ern portions. Latest guidance suggests FG will
develop late tonight impacting srn and ern portions of the CWA
where radiational cooling will be greatest.

.LONG TERM:  (Wednesday through Next Tuesday)
Issued at 309 PM CDT Tue Sep 16 2014

(Wednesday through Friday)

Main concern continues to be rain chances tomorrow into tomorrow
night over mainly central and southeast Missouri.  GFS/NAM/ECMWF are
still in relatively good agreement in dropping a weak shortwave
trough across Missouri during the day tomorrow.  Each of these
models shows some weak low level moisture lingering across central
and southeast Missouri into Wednesday night, so will continue a
chance of showers and thunderstorms in this area.   This scenario is
depicted pretty well at least through 00Z by the reflectivity on the
NSSL WRF.  Thereafter will maintain a dry forecast Thursday and
Friday as a surface ridge moves across the area at the same time a
upper ridge builds in from the west.

Went on the cooler side of guidance for highs the next couple of
days given the easterly surface flow and it matches up better with
mixing down the 900mb temperatures.   Likewise followed the cooler
NAM MOS for lows.

(Saturday through next Tuesday)

While there is still some disagreement between the GFS/ECMWF
regarding the speed and depth of a trough that will pass through the
area this weekend, it still appears that the attendant cold front
will move through on Saturday night and early Sunday.  Will keep
chances of showers and thunderstorms going Saturday into Sunday.
Will keep Monday and Tuesday dry at this point as we will be on the
back side of the the upper trough, though the latest runs of the GFS
is showing a secondary through dropping down in the northwesterly
flow on Tuesday.  This is a new trend that the ECMWF is not
showing.  Still expect at or just above normal temperatures ahead of
the front on Saturday before they drop back below normal for early
next week given expected 850mb temperatures in the 6-9C



.AVIATION:  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1104 PM CDT Tue Sep 16 2014

Northwest flow aloft will keep the mid Fall like conditions in
place. Upper air wave will move through overnight to reinforce the
northwest flow. Models trying to generate precitation at the nose
of a low level (5000 ft) jet of 30 knots over the MO/KS border. So
far no sign of anything develping. COU looks to be the only
location with a shot at rain, but will keep them dry for now. Band
of 4k to 5k clouds rapidly advancing SE. That may put a stop to
any MVFR ceilings. Lower clouds over southern MO are slowly
expanding a bit to the north. Some fog at SUS and CPS will will
bring temporary MVFR conditions until the clouds arrive. Wednesday
looks to be VFR.

Specifics for KSTL: 4k to 5k deck should arrive from 08 to 09z.
Will go with that and hold off on any MVFR ceilings. Lower clouds
over south central MO may work their way north and the MAV
guiidance brings them in for a short time. Not that confident they
will arrive, so will leave out for now.


IL...DENSE FOG ADVISORY until 10 AM CDT this morning FOR Bond IL-
     Clinton IL-Fayette IL-Marion IL-Washington IL.



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