Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180240
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
840 PM CST Wed Jan 17 2018

.UPDATE...
Issued at 840 PM CST Wed Jan 17 2018

The winds will remain steady from the southwest in the 10-15 mph
range tonight, in response to a persistently tight pressure
gradient. Illinois will be positioned between a clipper-like low
progressing across southern Canada into western Ontario, while an
expansive surface high pressure shifts south of Illinois toward
the Gulf of Mexico. A 40KT low level jet will affect NE Illinois
overnight, as possibly as far south as the I-74 corridor with
turbulent low level winds. Surface gusts to 20 mph could develop
at times after midnight, but stronger gusts should hold off until
mid-late morning tomorrow.

Despite very little cloud cover tonight, hourly temperatures look
to be nearly stationary due to steady SW winds, and warming mid-
level temperatures. One fly in the ointment is that our SE areas
with snow cover already dropped to near or below forecast lows
due to initial decoupling of the winds over deeper snow.
Therefore, the main update this evening will be to do slight
warming in the W-NW areas where warmer air will arrive first, and
slight cooling in the SE counties.

A more noticeable warming trend will start on Thursday, as highs
climb to freezing or above for the first time in a few days. Even
warmer temps are on tap for Fri-Sat-Sun, with increasing rain
chances late this weekend.

&&

.SHORT TERM...(This evening through Thursday)
ISSUED AT 153 PM CST Wed Jan 17 2018

With high pressure drifting into the lower Mississippi Valley,
winds have started to turn southwest across central Illinois.
A tightening pressure gradient will keep the speeds up somewhat
overnight, which should help keep temperatures from free-falling.
Lows should be 10-15 degrees (above zero), coldest over the south
where the winds will be lighter. The warming trend should begin in
earnest on Thursday, as temperatures reach above freezing over the
CWA. Mostly clear skies are expected to prevail through the
period.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 153 PM CST Wed Jan 17 2018

Upper ridging will build eastward through the end of the week,
with the warming trend continuing. Little change needed for
temperatures through the weekend, with 40s returning Friday and
most areas in the 50s by Sunday.

Main concern during the period remains with the late weekend storm
system. An upper level trough will dig across the southwest U.S.
early in the weekend, with a low closing off on Sunday over the
central Plains. The latest GFS is a bit quicker than the European
or Canadian models on the speed of this low lifting northeast.
This results in the cold front coming through late Sunday night
vs. Monday morning. While the shear with this front is fairly
decent, the timing results in little in the way of instability.
Can`t rule out a few rumbles of thunder, but chances are low
enough to keep a mention out of the forecast at this point.
Highest rain chances will be Sunday night into Monday morning.
However, wraparound moisture will keep some scattered rain or snow
showers lingering into early Tuesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 600 PM CST Wed Jan 17 2018

The cold dry air mass will produce nearly cloud-free skies over
the next 24 hours. The main issue tonight will be the potential
for LLWS conditions, mainly for our northern terminals. A speed
max between 925-850mb will advance across northern Illinois, with
the 40KT contour down to the PIA and BMI areas 04z and 15z. Have
continued with LLWS in those two TAFs, but may be adding the other
sites based on VAD wind observations and RAP/HRRR updates. BUFKIT
analysis show the remaining terminals only a few knots below 40kt
at 1000FT AGL.

After initial decoupling of the winds early this evening, surface
winds look to increase from the southwest to 10-14KT for a
majority of the night. After sunrise tomorrow, and an increasing
mixing heights, wind gusts could increase over 20KT at times.


&&

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

$$

UPDATE...Shimon
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Shimon



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