000
FXUS63 KILX 121750
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1150 AM CST Thu Dec 12 2013

.DISCUSSION...
ISSUED 1045 AM CST Thu Dec 12 2013

The forecast was updated around 8 am with the wind chill advisory
for the northern 7 counties ending at that time. May need to update
again for more mid/high clouds streaming se across the central and
especially ne counties. Wind chills still in the single digits
below zero this morning but gradually coming up with the air temps.
Highs look on track today in the mid to upper 20s, with areas sw of
Springfield in the lower 30s.

Strong 1039 mb arctic high pressure over the mid MS valley into
eastern AR and central Texas was ridging ne across the Ohio river.
This high brought another very cold night/morning to central/se IL
with several cities getting down to zero to 5 below with Mount
Carmel airport at 6 below and Altona 8 below zero. Increasing sw
winds over central IL to brisk levels with 15-20 mph. Temps
generally in the teens at 1030 am, ranging from 5F at Mount Carmel
Airport to 22 in Jacksonville. Mid/high clouds to continue to
stream se across central and se counties today with more sunshine
in sw counties. Dry conditions expected over central/se IL through
Friday morning.

07

&&

.AVIATION...
ISSUED 1150 AM CST Thu Dec 12 2013

VFR conditions expected to continue across the central IL terminal
airports through 18Z/noon Friday. Some mid/high clouds streaming se
across the central and northeast CWA with SPI on the edge of these
10-20k ft clouds through this evening. These clouds associated
with an elongated short wave from the northern plains se into
central/ne IL, and will gradually shift ne of central IL toward
overnight. Mid/high clouds may scatter out for a time during
overnight, but increase again during Friday morning ahead of
approaching storm system over southern CA. Snow not expected to
develop over central IL until during Friday afternoon. Brisk nw
winds 13-18 kts with gusts 18-23 kts early and mid afternoon to
veer ssw and diminish to 5-9 kts by sunset and continue through
Fri morning. Strong 1039 mb arctic high pressure over eastern AR
and ridging from central Texas ne into the ohio river valley to
weaken to 1029 mb along the Carolina coast by 18Z/noon Friday
while 1006 mb low pressure develops over the Texas panhandle by
Friday afternoon. Light to moderate snows expected to develop
during Friday afternoon and continue Friday night over central IL
to bring worse conditions after the 24 hour TAF forecast.

07

&&

.PREV 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

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$