Area Forecast Discussion
Issued by NWS Central Illinois

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578
FXUS63 KILX 221758
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1258 PM CDT Sun Oct 22 2017

.UPDATE...
Issued at 1045 AM CDT Sun Oct 22 2017

Updated the forecast to address chances of showers and isolated
thunderstorms today. Otherwise rest of forecast looked on track.
Breezy south winds 10-20 mph and gusts of 20-30 mph ahead of the
cold front from I-55 east to turn nw as the cold front pushes east
toward the IL/IN border by 00Z/7 pm. Highs to range from the lower
60s from Galesburg and Jacksonville west, to the mid 70s by the
Wabash river.

A cold front was just west of I-55 late this morning and its
eastward progress has slowed in past few hours. Brunt of showers
and isolated thunderstorms had lifted NNE into northeast IL and
southeast WI. Scattered showers were in eastern IL and some
lighter rain showers behind/west of the cold front. Rainfall
amounts have been fairly light east of the IL river generally less
than a tenth inch with a few spots getting up to a quarter inch.
Some bands of quarter to half inch amounts west of the IL river
since overnight. 1030 am temperatures ranged from mid 50s from
Macomb to Pittsfield west to the MS river, to around 70F at
Champaign, Lincoln and Springfield ahead of the cold front.

Latest hi-res models show showers becoming more widespread over
central and eastern IL east of the IL river during the afternoon
as cold front moves through with isolated thunderstorms possible
yet in eastern IL this afternoon.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 335 AM CDT Sun Oct 22 2017

08z/3am surface analysis shows a slow-moving cold front
approaching the Mississippi River. Most of the precipitation
has been occurring along and just behind the front...with very
little further east into central Illinois. Latest radar trends are
beginning to show showers becoming more numerous as far east as
the Illinois River Valley: however, the bulk of the precip remains
further west in the immediate vicinity of the boundary. With the
front moving very slowly eastward and individual showers generally
tracking N/NE, have slowed the arrival of rain across the KILX CWA
this morning. Based on radar trends, have kept locations near the
Indiana border dry until around 14z/9am. Most high-res models show
showers spreading into the area this morning in a diminishing
state, then re-developing across the eastern half of the area this
afternoon. End result will be a showery day, with perhaps a couple
rumbles of thunder. High temperatures will range from the lower
60s northwest of the Illinois River...to the middle 70s in the
Wabash River Valley.

An upper wave currently evident on water vapor imagery over the
Oklahoma/Texas panhandles will track eastward and eventually close
off across the Lower Mississippi River Valley tonight. As it does,
it will slow the eastward progression of the cold front and keep
rain chances alive across much of the area tonight. Will bring the
showers to an end along/west of I-55 overnight, but keep high
chance to likely PoPs in the forecast further east across the
remainder of the area. Low temperatures will range from the middle
40s in the Illinois River Valley...to the middle 50s near the
Indiana border.

.LONG TERM...(Monday through Saturday)
ISSUED AT 335 AM CDT Sun Oct 22 2017

Showers will persist across the eastern KILX CWA through Monday as
surface low pressure tracks along the slow-moving boundary into
the Ohio River Valley. Once the low lifts further northeast, the
best rain chances will depart: however, with an upper wave digging
southward into the region on Tuesday, widely scattered showers and
much cooler weather will be on tap. With 850mb temps progged to
drop to around -3C, high temperatures will struggle to reach the
lower 50s on Tuesday. Another cool fall day is expected on
Wednesday before temperatures make a temporary rebound back into
the middle to upper 60s on Thursday.

After that, a significant cooling trend is expected by the end of
the week: however, major timing differences exist among the
operational models concerning the timing of the approaching upper
trough responsible for the cooler conditions. The 00z Oct 22 GEM
is faster with this feature, showing a closed upper low tracking
north of central Illinois into the Great Lakes by Saturday
morning. Meanwhile, the GFS and ECMWF are considerably slower,
with the ECMWF showing the closed low meandering eastward into the
Great Lakes by Monday. With such a large spread in model
solutions, forecast confidence beyond Thursday remains poor. At
this point, will continue to forecast showers on Friday as the
upper trough and its associated cold front approach from the west.
Beyond that, the precip forecast is murky at best...depending on
which model verifies. What is certain however, is that temps are
going to take a nosedive at some point this weekend...setting the
stage for the coldest weather thus far this fall season by early
next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1255 PM CDT Sun Oct 22 2017

A strong cold front was near or just east of I-55, recently
passed through SPI and about to pass through BMI early this
afternoon. This front will pass east through DEC and CMI during
mid afternoon from 19-21Z. Mainly light rain showers and some fog
to drive vsbys down to 1.5-3 miles at times with IFR to MVFR
ceilings this afternoon especially behind the cold front. Latest
models continue to show light rain spreading ne across much of
central IL especially from IL river east during much of tonight
and diminishing in east central IL toward midday Monday. lower
ceilings to lift to VFR during overnight into Monday morning
starting at PIA 1st and getting to CMI last. Strong south winds
ahead of cold front with gusts 25-35 kts at BMI, DEC and
especially CMI to turn NW and still have gusts of 20-25 kts this
afternoon. NW winds to gradually subside to around 10 kts or less
during tonight and continue Monday morning.

&&

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

$$

UPDATE...07
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...07



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