471
FXUS63 KILX 061109
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
609 AM CDT Sun Jul 6 2025

.KEY MESSAGES...

- Chances of showers and thunderstorms returns to central and
  southeast IL today and evening, and lingering chances in
  southeast IL on Monday. Locally heavy rainfall, lightning and a
  few strong wind gusts are possible mainly this afternoon into
  mid evening mainly from I-55 east.

- Very warm and humid conditions will continue today with highs in
  the mid to upper 80s in central IL and afternoon heat indices in
  the low to mid 90s. Highs in the lower 90s southeast of I-70
  today with afternoon heat indices in the upper 90s to near 100.
  in the mid 90s to near 100 degrees. More seasonable temperatures
  along with humid conditions can otherwise be expected the next
  several days.

- Occasional periods of scattered showers and thunderstorms can be
  expected for the upcoming work week.

&&

.DISCUSSION...
Issued at 345 AM CDT Sun Jul 6 2025

The 08Z/3 am surface map shows a cold front over southwest WI to
near the IL/IA border and into nw MO. Radar mosaic shows scattered
convection over northern MO into west central and nw IL into
southeast half of WI. The convection was weakening in west central
IL as it was moving east toward the IL river by Beardstown. Bands
of clouds were over much of CWA except from Danville to Flora east
where clear to mostly clear skies still prevailed. Patchy light
fog in far se IL near the KY border. Muggy temps were in the low
to mid 70s at 3 am (80F at Decatur) with dewpoints in the upper
60s and lower 70s.

Tropical Storm Chantal with 50 mph winds at 4 am CDT was moving
inland near the Georgetown Airport on northeast coast of South
Carolina, or 70 miles northeast of Charleston SC and moving NNW
at 8 mph.

Closer to home in Illinois, the cold front is forecast to push
southeast over the IL river valley during this afternoon. Daytime
heating of unstable tropical airmass to ignite additional bands of
convection over central IL and into southeast IL late this
afternoon and evening. CAPES rise to 1400-2200 j/kg this afternoon
(highest from I-55 southeast) with weak wind shear values over
area today. SPC Day1 outlook does not have a marginal risk of
severe storms over IL today, but could be a few pulsey multicells
with strong winds. Very high PW values of 2-2.3 inches also could
give locally heavy rain in spots this afternoon into mid evening.
LPMM shows isolated spots of 1.5-3 inch rainfall amounts from I-55
se to I-70 this afternoon until dusk, with even a one or two
spots of 3-5 inches in east central IL. Rainfall amounts will be
quite variable today with some areas seeing less than a tenth
inch. Flash Flood Guidance (FFG) values are fairly high with lack
of widespread/heavier rainfall since Wed/June 18. The 1 hour FFG
values of 1.75-2.25 inches, 3 hour FFG values 2-3 inches, and the
6 hour FFG values of 3-4 inches. WPC ERO has marginal risk of
excessive rainfall this afternoon/evening from I-55 southeast.
Humid conditions linger today with very warm highs today in the
mid to upper 80s in central IL (coolest nw of the IL river) to
lower 90s se of I-70 where heat indices peak in the upper 90s to
near 100F. Heat index values in low to mid 90s this afternoon over
much of central IL.

The front to move slowly southward over central IL tonight and
into southeast IL on Monday. Convection chances to shift southward
with the front during tonight and Monday, with pops mainly in
southeast IL on Monday especially during Mon afternoon. Locally
heavy rain possible over far SE CWA on Monday afternoon though WPC
has shifts marginal risk of excessive rainfall into southern IL.
Highs Monday in the mid 80s in central IL and upper 80s from
highway 50 south where afternoon heat indices in the lower 90s in
southeast IL Monday.

Dry conditions return to CWA Monday night and Tue morning with
lows Mon night in the mid to upper 60s (lower 60s ne of I-74).
Very warm and humid Tue with highs in the upper 80s to near 90F
and afternoon heat index values in low to mid 90s. A short wave
trof moving into IL Tue evening to bring isolated convection Tue
afternoon and 20-30% chance of convection Tue night. SPC Day3
outlook has marginal risk of severe storms for winds and possible
hail far western CWA border Tue evening. WPC ERO also has marginal
risk of excessive rainfall over much of area Tue night. The upper
level trof over IL Wed keeps chances of convection especially Wed
afternoon/evening in warm/humid air mass. WPC ERO has marginal
risk of excessive rainfall over central and sw IL Wed
afternoon/evening. Highs Wed in the mid to upper 80s.

Diurnally enhanced chances of convection continues Thu/Fri during
afternoon/evening hours and tropical heat and humidity lingers
with highs in the upper 80s to around 90F. A northern stream short
wave trof moves into the upper MS river valley Friday and
continues chances of convection late this week (Fri/Sat).

07

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 610 AM CDT Sun Jul 6 2025

Some lower clouds have recently developed, as hinted by earlier
ensembles, resulting in some MVFR conditions at KPIA/KBMI.
Overall, this should improve by mid morning. Main focus during the
afternoon will be with development an west-east line of showers
and thunderstorms ahead of a cold front. This appears most favored
from KSPI-KCMI but exact placement is still a question, so will
continue with a PROB30 TSRA mention for these sites with some
refinement in the times. By mid evening, any residual storms
should be south of this corridor.

Later in the night, concern shifts toward a lowering of ceilings,
as northeast winds tap into cooler air coming off Lake Michigan.
Latest NBM guidance pegs chances of MVFR ceilings around 40% by
06z and reaching near 50% at KDEC/KCMI toward the end of the
period, while HREF has more of a focused ceiling drop lasting only
a few hours. Will go the more pessimistic route for now, with the
lowest ceilings in east central Illinois.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$