Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 231749

Area Forecast Discussion
National Weather Service Lincoln IL
1249 PM CDT Sun Jul 23 2017

Issued at 1035 AM CDT Sun Jul 23 2017

Trailing remnants of an MCS that passed through the southern half
of Illinois early this morning continue to produce a few showers
south of I-70 this morning. Meanwhile, a positive tilt upper
level trough evident on water vapor imagery remains across
northern Illinois, progged to progress southeast of the
central/southeast IL forecast area by 03Z. Ahead of the trough
axis, dewpoints remain quite high with low to mid-70s noted in
observations. Nevertheless, lower precipitable water behind the
trough axis should start mixing down through the afternoon
bringing a gradual reduction in surface dewpoints. With daytime
heating, over 3000 J/kg SBCAPE should be able to develop ahead of
the trough axis with at least weak lift and 30-35 kt sfc-6km bulk
shear, therefore isolated to scattered thunderstorms, some strong
to severe, should be able to develop in the afternoon to evening.
No significant updates needed to the afternoon/evening forecast
this morning. Earlier updates issued to continue scattered
showers and isolated thunderstorms along and south of I-70 a bit
later in the morning, which are now confined to a few of the
southeasternmost counties.


.SHORT TERM...(Today and tonight)
ISSUED AT 255 AM CDT Sun Jul 23 2017

Earlier convection that occurred generally along and east of I-57
late evening and past midnight has largely pushed into Indiana as
of 2 am. Currently watching a large MCS advancing across Missouri.
Trajectory of this would generally keep it south of I-72 as it
begins to move into western Illinois, with the HRRR showing a
diminishing trend as the remnants make it over to about Flora and
Effingham toward 7 am. SPC mesoanalysis still showing CAPE`s over
3000 J/kg at this early hour ahead of the MCS, with dew points at
Springfield almost 80 degrees at 2 am. As the day goes on, the
highest CAPE will shift over into southeast Illinois, as some
lower dew points start to advect into areas northwest of the
Illinois River. However, as the cooler air lags further behind,
temperatures reaching the lower 90s will still result in
significant instability over the northern CWA this afternoon. Will
maintain the mention of scattered storms this afternoon and
evening across the forecast area, as the cold front settles across
the region. Can`t rule out a few severe storms as 0-6km shear is
modest over the area (around 30-35 knots).

.LONG TERM...(Monday through Saturday)
ISSUED AT 255 AM CDT Sun Jul 23 2017

Quiet weather will dominate the first few days of the work week,
as high pressure drifts across the Great Lakes. The northeast
circulation into our area should keep dew points in check, mainly
mid 60s, through Tuesday. After that, the Gulf moisture flow kicks
back in as the upper level high builds eastward back into the
mid-Mississippi Valley. A strong upper low, currently seen in
early formation over northern British Columbia, will keep the
ridge from amplifying too much over us, so after a quick shot of
hot and humid weather, the upcoming end of week looks more

The main concern for precipitation will be Wednesday night into
Thursday, as the cold front trailing the upper low moves through
the area. The GFS introduces some scattered storms as early as
Wednesday afternoon as a weak wave moves through, but the ECMWF
focuses on the main front itself late Wednesday night into
Thursday. In either case, it should take until late Thursday
evening before the front fully crosses the forecast area, and will
keep healthy chance PoP`s going south of I-72 into the evening.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1249 PM CDT Sun Jul 23 2017

Lift associated with a trough crossing central IL this afternoon
will allow scattered cumulus cloud development at 3000-4000 feet
as well as isolated thunderstorm development from afternoon into
early evening. With the trough axis east of the area by mid
evening, all thunderstorms should end by 01-03Z. Overnight, humid
conditions and recent rainfall will allow some fog to develop,
however enough wind should continue overnight to keep visibility
reduction minimal. Have included tempo MVFR visibility 9Z-13Z for
fog potential. Winds NW 8-12 kts this afternoon decreasing to 4-8
kts and shifting to northerly overnight.





SHORT TERM...Geelhart
LONG TERM...Geelhart
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