Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190017

617 PM CST Thu Dec 18 2014

.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 00z TAFs through 00z Friday Evening)
Issued at 614 PM CST Thu Dec 18 2014

Expect mainly MVFR and IFR conditions through the period as there
is abundant low level moisture in the atmosphere and light winds.
Expect IFR conditions the next 24 hours at KCOU. The St. Louis
metro TAF sites are on the edge of a large area of IFR ceilings.
Expect current MVFR ceilings at KSTL and KCPS to slowly decrease
this evening to IFR after 06Z...and become LIFR between 10-17Z.
KUIN will see MVFR conditions most of the night...becoming LIFR
late tonight into late Friday morning. All locations should see an
improvement in ceilings and visibilities by late afternoon Friday.

Specifics for KSTL: Expect current ceilings to fall below 2000 ft
in the next hour or two with the onset of evening. 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...though
do not think they will rise above 2000ft at this time.





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