Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 201753

Area Forecast Discussion
National Weather Service Lincoln IL
1253 PM CDT THU OCT 20 2016

Issued at 1031 AM CDT Thu Oct 20 2016

Light rain continues to fall across east-central Illinois this
morning...with 1530z/1030am radar imagery showing most of the
precipitation along/east of a Champaign to Shelbyville line. As
low pressure tracks through the Ohio River Valley, these showers
will slowly pull eastward into Indiana by mid to late afternoon.
Meanwhile further west, a few very light showers or sprinkles will
be possible as a vigorous short-wave trough currently evident on
water vapor imagery over northern Missouri tracks across the area.
Some partial clearing is currently taking place along/west of
I-55: however, a large area of low cloud cover over eastern
Iowa/northern Illinois is expected to spill southward into the
KILX CWA this afternoon. End result will be a cool and mostly
overcast day. Due to the clouds and a brisk northerly breeze, high
temperatures will only reach the upper 50s to around 60 degrees.


.SHORT TERM...(Today and tonight)
ISSUED AT 239 AM CDT Thu Oct 20 2016

Scattered showers and isolated thunderstorms continue over about the
southeast half of the forecast area early this morning with the
greater concentration of steadier rains extending along and
southeast of a Champaign to Springfield line. Heaviest rainfall so
far has fallen south of I-72 to the I-70 corridor with areas from
Effingham to near Marshall (Clark county) receiving from 2 to 3
inches so far. Rainfall rates have decreased significantly in these
areas but light to moderate rains with isolated thunder should
continue for the next several hours.

An area of low pressure and frontal boundary over extreme southern
Illinois should begin to shift off to our east and south today but
cyclonic flow around the departing wave and a deepening 500 mb trof
tracking east across the Midwest will keep showers going into at
least the middle of the afternoon for areas east of Interstate 55.
With the cloud cover, scattered showers and gusty northerly winds
today, temperatures will be held down this afternoon with readings
in the upper 50s to lower 60s, coolest in the east and southeast
where the showers will be more persistent today.

The low will continue to move away from our area tonight with
clearing skies and chilly temperatures. High pressure will shift
from the central Plains east to just west of our area by 12z Friday
which should result in the coolest temperatures across the west and
northwest, closest to the ridge axis. We look for lows to drop into
the mid 30s northwest with patchy frost, to the lower 40s southeast.
It still appears the better setup for more widespread frost will
be to our northwest Friday morning, closer to the surface high.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 239 AM CDT Thu Oct 20 2016

Rather quiet period expected during much of this part of the
forecast. Deep upper trough will be swinging into the eastern U.S.
on Friday, allowing for a period of zonal flow this weekend before a
ridge starts to build across the Rockies on Sunday. This ridge will
amplify some early next week and shift toward the Mississippi
Valley. However, a shortwave will be tracking toward the Midwest,
arriving across Illinois on Wednesday. The GFS is stronger with this
wave and quickly pushes a storm system with showers and a few
thunderstorms through on Wednesday. The weaker ECMWF has a warm
front lingering just to our north for a time Tuesday and Tuesday
night, bringing an extended period of showers across the northern
half of the forecast area before the wave pushes through. For now,
will focus on the faster solution and limit the PoP`s to Wednesday.

Coldest part of the forecast will be on Friday, as another surge of
colder air is drawn down behind the departing trough. With 850 mb
temperatures around -2C, highs should only reach the mid 50s in most
areas, and the chilliest temperatures Friday night will be mainly
over the eastern CWA, with a touch of frost possible. After that, a
nice warming trend sets up, and upper 60s/lower 70s should prevail
for highs the first half of next week.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1253 PM CDT Thu Oct 20 2016

While the main area of rain from earlier this morning has now
shifted east of the terminals, a trailing upper-level wave may
bring a few light showers or sprinkles through the afternoon, so
have included VCSH at all sites. The main aviation forecast
concern will be the approach/timing of MVFR ceilings currently
spilling southward out of northern Illinois. Latest satellite
imagery shows the leading edge of the lower clouds along the I-74
corridor. HRRR seems to have a good handle on the clouds, so have
followed its solution closely. As a result, have initially started
with MVFR ceilings at the I-74 terminals...then have spread them
into KSPI/KDEC by 19-20z. With ridge of high pressure approaching
from the west, skies will gradually clear from west to east across
the area tonight. Based on forecast soundings, have scattered the
ceiling at KPIA by 02z...then further southeast to KCMI and KDEC
by 06z. Winds will initially be gusty from the N/NW this
afternoon, then will decrease to less than 10kt overnight into
Friday morning.


.ILX Watches/Warnings/Advisories...


LONG TERM...Geelhart
AVIATION...Barnes is the U.S. government's official web portal to all federal, state and local government web resources and services.