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000
FXUS63 KILX 041732
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1132 AM CST Wed Dec 4 2013

.DISCUSSION...
ISSUED 1000 AM CST Wed Dec 4 2013

Dense fog starting to slowly lift in some areas. Have lopped off a
few counties from the advisory from Springfield westward where
visibility has been more persistently around a mile or so. Seeing
some variable visibilities from Peoria northwest and also over the
southeast counties, and will evaluate over the next hour whether
to drop the advisory there too or let it ride until its natural
conclusion at noon. HRRR model showing a more persistent lifting
of the dense fog over the next couple hours, although the RAP
lingers it east of I-57 into early afternoon.

Latest surface map shows low pressure over central Missouri, with
a secondary low over south central Iowa which should become the
primary low late today. Should start seeing the cold front moving
into the Illinois River valley toward 5-6 pm and across most of
the CWA by 10 pm.

Geelhart


&&

.AVIATION...
ISSUED 1132 AM CST Wed Dec 4 2013

LIFR conditions continue to plague the TAF sites at midday, with
locally lower conditions near KBMI which has persistent visibility
near 1/16SM. Should see some slow improvements with ceilings and
visibilities this afternoon as visible satellite and surface obs
show some higher ceilings heading northward. Fairly good sized
area of central/eastern Missouri has lost most of its low clouds,
and the latest RAP guidance suggests areas around KSPI/KDEC could
potentially reach into VFR range for a couple hours around midday.
For now will keep broken cloud cover around 2500 feet there
mid/late afternoon.

Strong cold front will sweep through central Illinois this
evening, swinging winds around to the southwest. Guidance from the
RAP and NAM models show VFR conditions becoming likely after 06Z.

Geelhart

&&

.PREV DISCUSSION...
ISSUED 311 AM CST Wed Dec 4 2013

Main forecast concern continues to be potential for accumulating
snow and ice across parts of central Illinois late Thursday into
Friday.

SHORT TERM...Today through Friday

Widespread fog once again blankets the area early this morning.
Moist low-level airmass remains in place, with 08z/2am surface
dewpoints well into the 40s. This ample moisture combined with
light winds will allow visibilities to continue to drop over the
next couple of hours. NAM/GFS forecast soundings and latest HRRR
visby forecast all point to widespread dense fog through much of
the morning. Will therefore be issuing a Dense Fog Advisory for
the entire KILX CWA through midday. Fog will gradually dissipate
by early afternoon, although visibilities will continue to be
somewhat limited until cold front pushes through late this
afternoon into the evening. Despite FROPA later today, shallow
moisture below 5000ft will limit precip potential. Will therefore
only mention isolated showers today into this evening. High
temperatures will be quite a bit warmer than they were yesterday,
but will be tempered by the fog/clouds to some extent. Will go
near or slightly above MAV guidance numbers, but not as high as
the warmer MET. Resulting highs will mainly be in the upper 50s
and lower 60s.

Once front passes, much colder air will arrive tonight into
Thursday. Overnight lows will drop into the upper 20s and lower
30s across much of the area, but will remain in the upper 30s
further east near the Indiana border. High temperatures on
Thursday will not rise much from the early morning lows, with
readings ranging from the upper 20s along/west of the Illinois
River to around 40 degrees along the Wabash River.

Models are in good agreement with the development of wintry precip
across parts of central and southeast Illinois late Thursday into
Friday, with a few minor differences still remaining. NAM has
slowed the onset of precip until early evening, while GFS/ECMWF/GEM
still bring it in during the afternoon. Given drier airmass behind
departing front, think NAM may have the right idea. Will therefore
delay initial precip development until late afternoon, with main
push arriving during the evening. Airmass will be cold enough to
support snow across most of the area: however, warm layer aloft
with max temps of around 4C supports mixed phase precip along and
south of I-70. Late afternoon surface temps in the upper 30s to
around 40 will allow for mainly rain along and south of highway
50. As the evening progresses, deepening cold layer will allow for
a gradual change over to mainly snow across the SE KILX CWA
overnight, although areas along and south of highway 50 may
experience a period of freezing rain as surface temps dip below
32 degrees. Any icing will be minimal, as precip transitions to
snow/sleet after midnight.

Initial wave of precip wanes after midnight, followed by another
wave on Friday. Model differences here focus on how far into the
cold airmass to spread the precip. NAM is most aggressive, while
GFS remains further southeast. Given strength of approaching high
within the cold airmass, think GFS solution is most logical. As a
result, will focus highest POPs for snow across the E/SE CWA. Once
the wintry precip ends Friday afternoon, total snowfall
accumulations of 3 to 5 inches will be likely along and south of
I-70. Amounts will steadily decrease further northwest, with up
to 1 inch possible along a Jacksonville to Danville line. Further
north, only a few flurries are expected along and north of a
Rushville to Bloomington-Normal line.

LONG TERM...Saturday through Tuesday

Cold weather will prevail throughout the extended, with only a brief
moderation in temps expected on Sunday. Models continue to show
another short-wave trough digging southward into the western
CONUS this weekend, resulting in downstream ridging over the
southeast states. As flow becomes more southwesterly aloft,
frontal boundary along the Gulf Coast will get pushed back
northward Sunday into Monday. It appears deepest moisture and
highest precip chances will remain southeast of Illinois across
the Tennessee and Ohio River Valleys, although the GFS is slightly
more aggressive in bringing precip further northwest into the cold
air than the ECMWF. At this point, will trend toward the ECMWF and
will only feature low chance POPs for snow Sunday and Sunday night
with minimal accumulations. After that, another very cold airmass
will drop into the Midwest by early next week, resulting in high
temps in the teens by Tuesday.

Barnes


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY until Noon CST today FOR ILZ027>031-036>038-
041>045-053.

&&

$$