Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 220541
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1141 PM CST Wed Feb 21 2018

.UPDATE...
Issued at 930 PM CST Wed Feb 21 2018

An initial wave of energy advancing across southeastern Illinois
this evening and just after midnight will keep light rain
continuing across our southeast counties, especially south of a
line from Shelbyville to Paris. The northern fringes of that
precip look to start as freezing rain, with some snow/sleet
possible. Light icing could develop on area roads, but overall QPF
looks to be less than a tenth of an inch, and most likely just a
few hundredths of an inch. Despite the light amounts, we will keep
the winter weather advisory in place, due to the potential impacts
that could occur later tonight into the morning commute, as
temperatures hover at or just below freezing the closer to I-72
and farther north you go. The first wave of precip looks to
diminish and shift east into Indiana before 5 am.

A second wave of energy, visible on satellite and in radar
returns in eastern Kansas, will progress northeast toward the
Illinois River valley later tonight. Light freezing rain is
expected to develop after 2 am, and progress across our northern
counties, mainly N of I-72. Once again, QPF amounts look to be a
few hundredths of an inch, but with surface temperatures quite a
bit colder tonight than last night prior to the precip arriving,
there is a little higher potential for some icing on roads, and
especially the bridges, overpasses and on/off ramps. Even a light
glaze of ice could cause significant impacts. Sleet or light snow
may mix in at times between 3 am and 8 am, adding to the potential
of slippery conditions. Air temperatures should rise above
freezing after 9-10 am tomorrow, which will help precip change
over to rain as it comes to an end. Will leave the northern winter
weather advisory going through Noon, with the expectation that the
counties will probably be able to be cleared from south to north
as warming occurs and precip diminishes.

Updated forecast info has been sent to the web.

&&

.SHORT TERM...(This evening through Thursday)
ISSUED AT 306 PM CST Wed Feb 21 2018
Cold front responsible for the drop in temps yesterday and today
has sagged south of the Ohio River Valley this afternoon as high
pressure dominates the Midwest on the CONUS surface map. Not a
classic high pressure weather day, however, as moisture trapped in
the boundary layer from the abundant precip from the past few days
has kept the region cloudy throughout the day. Northerly winds
trying to push drier air into Central IL... but dewpoints south of
Interstate 70 remain near the freezing mark. Precip just behind
the boundary south of I70 is expected to continue, albeit light
through the early evening. The first in a series of waves moving
along the southwesterly flow aloft will spread the precip
northward tonight after 00z. A warm nose in the forecast
soundings at midlevels indicate any ice that is introduced into
the layer will melt...and a wintry mix will become an issue for
Central Illinois. Temperatures hovering near freezing may result
in light glazing early on elevated surfaces. Unlike yesterday, the
ground has not gotten as warm today...and the expected sunshine
was limited by a more persistent cloud cover. Concerned that the
temps will have the chance to fall closer to the freezing mark a
little quicker after sunset. Have issued a Winter Weather Advisory
for the areas north of Interstate 70 for a wintry mix as the
precip spreads northward. Have segmented the advisory with an
after midnight start time in the northern portions of the forecast
area. The precip is expected to redevelop along another wave
moving into the region after midnight. Again, little more than a
glaze is anticipated in much of Central IL, but accumulations of
up of a few hundredths are possible south and west of a line from
Decatur to Galesburg. The morning commute may be somewhat
problematic in the morning, especially on bridges and untreated
roads. Temperatures hovering near the freezing mark, there will be
a quick shift back to rain in the morning hours for the southern
segment of the advisory... and by noon for areas along Interstate
74.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 306 PM CST Wed Feb 21 2018
Next wave has been delayed until after 00Z Thursday night...
ending by Friday midday. Temperatures are expected to remain warm
enough to keep the precip as rain... back to lows in the upper
30s/40s... and highs in the upper 40s/low 50s on Friday.

The next, and stronger system lifts into the region on Friday
night...spreading more precip northward. Significant precipitation
will be expected with this storm. With the saturated ground
already ahead of this system, flooding concerns will linger into
the weekend. Heaviest rainfall will be anticipated south and east
of Interstate 55 through Saturday night. Forecast dries out on the
other side of the cold front Saturday night. Temps are cooler but
still above normal for the first half of the work week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1141 PM CST Wed Feb 21 2018

Steady northeast winds will continue the rest of the night as a
stalled cold front lingers just south of the Ohio River Valley. A
baroclinic zone extending across southeastern IL is continuing to
be a focal point for rain showers. Warm air overrunning the low
level cold dome will fuel rain or freezing rain, possibly mixed
with sleet. That precip should be mainly along and south of I-72
through 2 am, before the initial wave of precip shifts east into
Indiana late tonight. Also late tonight, another surge of precip
is forecast to push into our west-central counties, and affect
mainly SPI, PIA, and BMI. That precip could start as FZRA or
snow/sleet, then warming temps will change that precip to rain
after 15z or so.

Travel surfaces could see a light glaze of ice tonight and early
in the morning, due to colder ambient surface and ground temps
than last night.

Wind speeds will remain 10-15kt for most of the next 24 hours,
with wind directions shifting from NE to East tomorrow afternoon,
and SE tomorrow evening. Precip should diminish or end by
afternoon with the second wave. A third wave will arrive Thursday
evening from the west, with precip as all rain in milder temps.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon CST Thursday for ILZ027>031-
036>038-040>043-047-048.

Winter Weather Advisory until 9 AM CST Thursday for ILZ044>046-
049>057-061.

&&

$$

UPDATE...Shimon
SHORT TERM...HJS
LONG TERM...HJS
AVIATION...Shimon


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