Area Forecast Discussion
Issued by NWS Central Illinois

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181
FXUS63 KILX 220835
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
335 AM CDT Sun Oct 22 2017

.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 06Z TAFS through 06Z Sunday night)
Issued at 1110 PM CDT Sat Oct 21 2017

Little change from previous discussion. The main forecast
challenge will be timing of the main precipitation shield
currently out to our west into our TAF area. Initially, it
appears the PIA and SPI TAF sites will be affected by the showers
and storms, with a gradual shift further east Sunday morning as
the front edges across the area. VFR cigs will be replaced by
MVFR cigs at PIA and SPI in the 10z-12z time frame, at BMI and
DEC in the 12z-15z period and by 18z at CMI.

Timing of the cold front from west to east still appears to be in
the late morning at SPI and PIA and by late afternoon, in the
19z-22z time frame at CMI as the front slows down its eastward
progress later in the day. Southerly winds ahead of the front will
continue to gust up to 25 kts at times at most sites except DEC
and CMI where we will continue to hold on to LLWS at 1500 feet for
winds out of the south at 45 kts (based off the ILX VAD wind
profile) for several more hours until the precip arrives. Winds
will shift into the northwest at 10 to 15kts after FROPA with
model soundings showing drier air advecting in behind the front
resulting in a return to VFR conditions from west to east tomorrow
afternoon and evening with CMI the last to see their cigs
improve.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Smith



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