Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 130537
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1137 PM CST Thu Jan 12 2017

.UPDATE...
Issued at 840 PM CST Thu Jan 12 2017

High pressure centered over South Dakota this evening will
dominate our weather for the next 18 to 24 hours as much
colder air continues to filter southeast into central Illinois.
Current temperatures underneath the large cold fair weather
system were already in the -10 to -20 degree range over northeast
South Dakota into east central North Dakota. The center of the
coldest air will remain north of our area over the next several
days, however, the high will continue to feed cold and dry air
south into the Midwest, at least at the surface. However,
temperatures aloft will be warm enough to support mainly rain
around 3500-5000 feet above ground, unfortunately, here at ground
level thanks to the large high just to our north that will be
slow to move off, surface temperatures will have a tough time
warming to or above freezing over the next several days, except in
the southeast where we may see a few hours in the afternoon where
temperatures inch above the freezing mark.

The initial surge of freezing rain will push into southeast
Illinois Friday afternoon and inch its way north through tomorrow
night, fighting the affects of the drier air associated with the
area of high pressure over the central Great Lakes and confluent
flow aloft. The latest NAM-WRF agrees with this scenario in
bringing the first round into central Illinois during the evening
and then having a tough time getting to or north of I-74 later
tomorrow night. It appears what precip is able to make it to I-74
or north tomorrow night/Saturday morning will be quite light. The
more concentrated area of light freezing rain looks to be just
south of a Springfield to Paris line late tomorrow afternoon and
evening.

Overall, the current forecast has trends handled quite well with
no changes significant enough to warrant an evening ZFP update
at this time. No changes will be made to the current Winter
headlines in our area for later tomorrow through the upcoming
weekend. As additional model data comes in later this evening,
we will assess the icing threat for the next several days and
make the necessary changes/upgrades in the current winter
headlines, if needed.

&&

.SHORT TERM...(This evening through Friday)
ISSUED AT 319 PM CST Thu Jan 12 2017

A strong cold front has pushed southeast to near the Ohio river at
mid afternoon, taking rain showers southeast of CWA. Northwest winds
of 8-15 mph and few gusts to 20 mph were ushering in colder air to
central and southeast IL today. Mercury levels at mid afternoon
range from 22F at Galesburg to 42F at Lawrenceville and Mount Carmel
airport. Overcast stratus clouds below 1.5k ft over CWA were
breaking up in nw IL closer to 1033 mb arctic high pressure over
western ND and ridging into the central plains.

Latest forecast models take cold front southeast across KY/TN
tonight as arctic high pressure moves into the upper MS river valley
Friday morning. This should decrease clouds from nw to se late today
and into tonight and keeping precipitation south of CWA through
early Fri morning. Lows tonight range from mid teens from IL river
nw to the mid to upper 20s in southeast IL. Overrunning will set up
over southern CWA during Friday with clouds spreading back northward
during Fri morning as skies become mostly cloudy to overcast by
Friday afternoon. Also will see light freezing rain spread into
areas south of a Jacksonville to Mattoon to Robinson line by late
Friday morning and getting as far north as a Lincoln to Danville
line by sunset Friday. Northern fringe of system will also have
chance of sleet while south of I-70 could see light rain as well.
Will continue the winter storm watch for central and southern CWA
starting Friday afternoon, though the wintery mix may not reach
northern part of watch area from I-72 north until late Friday
afternoon. Highs Friday range from upper 20s nw of I-55 to the mid
30s in southeast IL.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 319 PM CST Thu Jan 12 2017

The frontal boundary stalling just southeast of the forecast area
and broad surface high pressure moving eastward through the Great
Lakes Region over the weekend will provide the main ingredients for
winter weather over the weekend into Monday morning as the high
feeds cold surface air into the area from the north/east, and the
frontal boundary allows a couple of disturbances to propagate
northeastward into the area brining precipitation. A persistent warm
layer aloft will cause any precipitation to fall as rain, however
temperatures will be below freezing for the nighttime periods...only
rising to near or a few degrees above freezing in the afternoon.
Highs will potentially get a bit more solidly above freezing south
of I-70 in the upper 30s. Therefore, periods of freezing rain can be
expected through the weekend, especially the nighttime periods.
Total ice accumulations could exceed a quarter inch from roughly I-
72 southward and I-57 westward, although at this point it appears
the breaks in accumulation and the potential melting in the
afternoon periods may prevent any ice buildup over one quarter inch
so have kept the winter storm watch going and have not upgraded any
portion to warning or advisory so far. Also added remaining portions
of northern CWA to the watch starting Midnight Saturday night and
going to Monday morning.

Strong warming expected to take place Monday as a low tracks NW of
the area bringing strong warm advection and heavier rainfall which
could result in rainfall up to an inch Monday through Tuesday.
Precipitation chances taper off through midweek and mainly based on
timing uncertainty with the progression of the early week low. Highs
expected to get to the 40s and 50s Monday through Thursday with lows
mainly 30s, possibly 40s Monday night.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1130 PM CST Thu Jan 12 2017

VFR conditions are expected to continue over most of the area with
the exception of SPI and DEC after 02z Saturday as MVFR cigs will
shift north into the area along with the threat for some light
freezing rain. Best timing of the onset of the light freezing rain
and possibly sleet will be from 21z-00z at SPI and DEC with cigs
gradually lowering to MVFR during the evening. Further north, will
carry VCSH at CMI and BMI, although confidence that any precip
will shift along or north of I-74 tomorrow evening is rather low
at this time as quite a bit of dry air will be fed south and
southwest into our area from a large Canadian high pressure area
to our north. Higher probabilities for the threat for ice will be
at DEC and SPI along with lower cigs, at least through this
forecast period. Surface winds will be north and then become
northeast on Friday with speeds around 10 kts tonight, and then
from 10 to 15 kts during the day Friday with a few gusts around 17
kts. Winds should veer more into an easterly direction Friday
night with speeds of 10 kts or less.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday afternoon through Sunday morning
for ILZ042>057-061>063-066>068-071>073.

Winter Storm Watch from Friday afternoon through late Sunday
night for ILZ040-041.

Winter Storm Watch from late Saturday night through late Sunday
night for ILZ027>031-036>038.

&&

$$

UPDATE...Smith
SHORT TERM...07
LONG TERM...37
AVIATION...Smith



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