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000
FXUS63 KILX 121153
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
553 AM CST Thu Dec 12 2013

.DISCUSSION...
ISSUED 250 AM CST Thu Dec 12 2013

High pressure centered over southern Illinois early this morning.
Earlier temperatures and wind chills which had been coldest early
in the evening have crept up a bit, but wind chills should start
to worsen again toward sunrise as the winds pick up from the
southwest. Thus will keep the wind chill advisory going across the
north through 8 am, although values may be a bit borderline for
reaching criteria again.

SHORT TERM...Today through Saturday:

Main forecast concern remains with winter storm system that will
be affecting the area Friday and Saturday. The models remain in
good agreement with synoptic features and timing, with the primary
issues being precip type and snow amounts.

Upper low currently spinning just southwest of San Diego will open
up as it moves through the Desert Southwest tonight. This wave is
expected to reach the mid Mississippi Valley by Saturday morning
as it phases some with the northern branch of the jet stream. Have
increased Friday afternoon PoP`s to around 60% across the far
southwest CWA, and around 50% elsewhere, with categorical PoP`s
during the night. In terms of amounts, latest thinking is that a
stripe of 4 to 5 inches is likely across central Illinois. Will
wait for one more set of model runs before issuing any headlines,
as some of the guidance is teetering on the edge of warning
criteria, and there is also the concern for precip types as
mentioned below.

Precip types and temperatures remain a bit of a challenge. The
00Z NAM, and to a lesser extent the GFS, initialized a bit oddly
with a significant warm temperature bulls eye across the southwest
CWA this afternoon and again on Friday. This may have been due to
the snow cover initialization which was a little too generous
across the remainder of central Illinois. Low level thermal
profiles on the NAM seem too high, with the NAM MOS guidance
giving a high of 40 at Springfield tomorrow. Leaned more toward
the GFS thermal profiles and MOS guidance as a result. Still
think some sleet is possible in the afternoon and early evening
before switching over to all snow. Southeast CWA may see some
freezing rain as well, although this is a bit more borderline
especially afternoon as temperatures will be near or just above
freezing. Precipitation on Saturday should end as some light rain
or drizzle, with temperatures above freezing in most areas.

LONG TERM...Sunday through Wednesday:

A shift toward a bit warmer pattern is still on tap early next
week, with more of a flow from the Pacific Northwest. The model
guidance diverges toward mid week, with the GFS bringing another
shot of Arctic air around Wednesday, whereas the ECMWF is about 20
degrees Celsius warmer with its 850 mb temperatures. The forecast
will have 30s in many areas for Monday-Wednesday. Any
precipitation is expected to remain to the north.

Geelhart
&&

.AVIATION...
ISSUED 553 AM CST Thu Dec 12 2013

VFR conditions expected to persist through the 12Z TAF valid
time. Mid/high level cigs will become more widespread/thicker with
time, but they will be well into the VFR category. Southwest
winds are expected through the period, becoming gusty at times
today, as return flow develops on the back side of a departing
surface ridge.

Bak
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY until 8 AM CST this morning FOR ILZ027>031-
037-038.

&&

$$