Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250415

1115 PM CDT Fri Oct 24 2014

Issued at 945 PM CDT Fri Oct 24 2014

Present indications are that we should see dense fog overnight
across portions of northeast Missouri into west central Illinois.
Its origin may be two-fold. First there could be some development
in the moist southerly flow ahead of the weak encroaching cold
front. However there may be a better probability in the wake of
this boundary as it moves into northern Missouri/western Illinois late
tonight. Quite a bit of dense fog has developed across the southeast
half of Iowa and trajectories overnight with the passage of the
front would bring this south-southeastward. Recent runs of the
HRRR have been suggesting this scenario which is also supported
by RH progs in the lowest 500 feet from the NAM and the RAP. I
have issued a dense fog advisory through 14z Saturday and
depending on trends overnight this may need to be expanded.



.SHORT TERM:  (Tonight through Sunday)
Issued at 332 PM CDT Fri Oct 24 2014

The last vestiges of this morning`s low clouds and fog is finally
dissipating.  However, clearing sky and light wind combined with
relatively high dewpoints in the mid and upper 50s tonight will
likely produce more fog.  A weak trof of low pressure now moving
through eastern Nebraska will also drop into the area providing a
little lift and convergence but not much of an increase in wind.
Unsure how low to go at this time, but at least patchy fog looks
likely with more widespread fog in northeast MO/west central IL.

Fog will likely linger into the daytime hours of Saturday morning.
A lot of uncertainty as to how long...but at least through 14-15Z
seems likely.  The trof is expected to come to a halt Saturday
afternoon/evening near the MO/AR border then begin lifting back to
the north as a warm front as warm advection begins ahead of the next
system.  The warm front continues lifting north Sunday and decent
mixing should give us temperatures well above normal.  MOS
temperatures through Sunday look pretty reasonable so have followed
them closely.


.LONG TERM: (Sunday Night through Next Friday)
Issued at 344 PM CDT Fri Oct 24 2014

Sunday night into Monday the next strong shortwave moves from the
Rockies into the Great Plains.  Strong warm advection should keep
temperatures pretty mild...more summer-like in fact...into Monday
afternoon.  As the surface cold front associated with the shortwave
approaches the area Monday night, expect scattered showers and
possibly a few thunderstorms to affect the area.  Kept PoPs in the
high chance/low likely range as the front moves through the area
late Monday night into Tuesday.  Rain chances should be more or less
done by 00Z Wednesday.  Cooler conditions for the rest of the week
as the upper pattern amplifies with a deep trof over eastern North
America and a strong ridge over the Rockies. A shortwave is forecast
to ripple by Thursday which could produce another round of light
rain, tho differences in medium range guidance indicate slight
chance PoPs are the best way to handle it at this time.  Next Friday
looks cool and dry at this time as a strong Canadian high pressure
system slides down into the Mississippi Valley.



.AVIATION:  (For the 06z TAFs through 06z Saturday Night)
Issued at 1033 PM CDT Fri Oct 24 2014

A weak cool front will move southeastward through the area late
tonight. Fog is expected to develop and/or advect southward into
our area from IA and nwrn IL late tonight along/ahead of this
front. Patchy stratus clouds is also possible as well, due to
light surface winds near the front and relatively high surface
dewpoints along and south of the front. The lowest visibilities
will likely be in UIN where they may drop to one quarter of a mile.
This fog will dissipate by late Saturday morning. A s-swly
surface wind will veer around to a nwly direction late
tonight/early Saturday morning after fropa. The surface wind will
become n-nely Saturday evening, albeit light as a surface ridge
moves through the region.

Specifics for KSTL: Just high level clouds late tonight and maybe
scattered low level clouds as well. Light fog can be expected late
tonight/early Saturday morning. A s-swly surface wind will veer
around to a nwly direction early Saturday morning after fropa. The
surface wind will become n-nely Saturday evening, albeit light.



MO...DENSE FOG ADVISORY from 3 AM to 9 AM CDT Saturday FOR Knox MO-
     Lewis MO-Marion MO-Shelby MO.

IL...DENSE FOG ADVISORY from 3 AM to 9 AM CDT Saturday FOR Adams IL-
     Brown IL.



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