Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190543

1143 PM CST Thu Dec 18 2014

Issued at 957 PM CST Thu Dec 18 2014

Stratus and stratocumulus clouds along with fog can be expected
for the remainder of the night. The lowest visibilities will occur
across portions of central and southeast MO where fog may become
dense late tonight. There is less fog potential across west
central and southwest IL where the near surface layer was drier.
Low temperatures will be a little colder in this area as well
underneath the surface ridge axis.



.SHORT TERM:  (Through Late Tonight)
Issued at 206 PM CST Thu Dec 18 2014

Any lingering flurries or drizzle will taper off late this
afternoon. Increased low-level moisture from today`s snowfall
along with light winds overnight will create favorable conditions
for fog formation. Later shifts will need to monitor the potential
for dense fog.


.LONG TERM:  (Friday through Next Thursday)
Issued at 206 PM CST Thu Dec 18 2014

An upper trough and its associated surface low will move across
the central and southern CONUS tomorrow and tomorrow night. Light
rain/snow is possible across southern/southeastern MO into
southern IL, but the bulk of the precipitation will occur south of
the LSX CWA. A separate vort max drops down from Canada into the
back side of the upper trough before it swings through southern IA
on Fri night/Sat. This feature could provide upper support for
sprinkles/flurries across northern MO and west central IL if
sufficient moisture becomes available.

A clipper-like system is forecast to develop over the northern
plains/western Great Lakes on Sunday night into Monday, then close
off over the northeastern quadrant of the CONUS during the middle
of the week. The GFS and ECMWF exhibit differences regarding
timing (ECMWF is slower), vort intensity (GFS is more intense),
and the result of interactions with other disturbances. If this
low pressure system develops as currently advertised, then it
would be expected to produce widespread rain/snow between Monday
and Wednesday with clouds and flurries lingering into the middle
of the week within a cyclonic flow regime aloft.

Temperatures will be seasonably cool on Friday and Saturday, then
warm to around 5-7 degrees above average on Sunday and Monday
ahead of the clipper-like system. Expect cooler temperatures for
the middle of next week within the colder air behind the clipper



.AVIATION:  (For the 06z TAFs through 06z Friday Night)
Issued at 1142 PM CST Thu Dec 18 2014

Extensive area of IFR conditions currently cover most of central
Missouri reach to just west of the St. Louis metro area and just
southwest of KUIN.  Expect KCOU to remain IFR until mid afternoon
on Friday. Expect that ceilings and visibilities will slowly fall
at KUIN and the St. Louis metro TAF sites the remainder of the
night, and then slowly improve back to MVFR by late morning or
early afternoon on Friday. Winds will remain light through the

Specifics for KSTL:  Expect current ceilings to fall below 2000 ft
in the next hour or two as large area of IFR conditions just west
of the terminal moves east. Then ceilings and visibilities will
likely slowly decrease through the night given the high atmospheric
moisture and light winds. LIFR conditions are still expected
between 10-17Z. Do expect some slow improvement in ceilings and
visibilities during the afternoon hours, with ceilings increasing
above 2000 feet after 22Z.





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