Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 160020

720 PM CDT Mon Sep 15 2014

Issued at 545 PM CDT Mon Sep 15 2014

Quick update to the forecast this evening to account for area of
drizzle that has developed in the wake of the front.



.SHORT TERM:  (Through Late Tonight)
Issued at 258 PM CDT Mon Sep 15 2014

Focus tonight will be RA/DZ and FG development.

Sfc low and fnt are slowly moving thru the region this afternoon.
Mdls are in good agreement with this system pulling out of the
region this eve. Behind the fnt, low clouds and DZ linger with an
isod shower. Will keep slight chance PoPs for portions of the CWA
this evening, then mention DZ and FG overnight. Mdls suggest nrn
portions of the CWA will clear out this eve allowing temps to
quickly drop and FG to potentially form. Uncertainty remains how
low vsbys will drop as nly winds will help advect dry air into the
region. Have added patchy FG for areas along and N of a line from
KJEF to KPPQ. Elsewhere, will leave mention of DZ with low clouds
lingering thru the night and based on upstream obs. This line,
between FG and DZ, may need to be moved as the evening progresses.


.LONG TERM:  (Tuesday through Next Monday)
Issued at 258 PM CDT Mon Sep 15 2014

(Tuesday through Thursday)

Some patchy fog and drizzle will persist through mid morning Tuesday
before mixing kicks in and skies begin to clear.  Then expect
dry weather the rest of the day and on Tuesday night as we will lie
under neutral or subsident motion under northwesterly flow aloft.
Still expect scattered showers and thunderstorms Wednesday and
Wednesday night over central and southeast Missouri as the
GFS/NAM/ECMWF are all in good agreement that a weak shortwave will
move southeast across Missouri late in the day.  This system will
have some corresponding low level moisture convergence to support
it.  Have left Thursday dry as upper ridge will be building into the
area from the west.

High temperatures are mainly a blend of MOS guidance which are
supported by mixing down 900mb temperatures.  Low temperatures
follow the agreeable MOS guidance.

(Friday through Monday)

Still expect temperatures to warm up to near normal on Friday and
Saturday as both the GFS and ECMWF are still progging 850mb
temperatures to reach the mid teens Celsius.  Friday still looks dry
before ascent increases ahead of a trough that will move through the
area over the weekend.  There is less agreement today than yesterday
with the details of the operational GFS and ECMWF regarding the
speed and depth of this upper trough.  Either way, it still appears
that a there will be a chance of showers and thunderstorms over the
area Saturday into Sunday as the attendant cold front moves across
the area.  By next Monday, the ECMWF is showing colder air working
into the area behind a deeper upper air trough than the GFS.  Will
lean toward climatology for temperatures behind the front for early
next week.



.AVIATION:  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 652 PM CDT Mon Sep 15 2014

Expect MVFR flight conditions and northerly flow will prevail this
evening across most of the area. A band of drizzle or light rain
stretching along the I-70 corridor will continue moving south with
cigs/vsbys dropping to IFR in some spots. Another band of
thunderstorms over southeast Missouri will continue moving south
and exit the area by 01Z. Lower confidence in the forecast after
06Z, but either IFR stratus or fog (perhaps both) is expected to
develop from central through east central Missouri into southwest
Illinois. Guidance shows flight conditions falling below airport
minimums during the predawn hours of Tuesday morning. Am not that
confident this will happen, but vsbys/cigs below AOB 1SM and 400FT
are certainly possible. IFR conditions should improve after 14Z
Tuesday morning.

Specifics for KSTL:

Band of light rain or drizzle will likely be through the terminal
shortly, which will necessitate an update to the TAF. Expect a
temporary increase in ceilings behind the drizzle, possibly up to
VFR conditions, but IFR cigs are lurking to the north/northeast
and expect that these lower ceilings will build southwest as the
evening cools. Guidance is indicating that vsbys/cigs will drop to
near or below airport minimums late tonight, but am not confident
this will occur. Still, with cool air filtering in behind the
front and drier air lagging, could see conditions AOB 1SM and
400FT during the predawn hours of Tuesday. IFR flight conditions
should improve after 14Z Tuesday morning.





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