397
FXUS63 KILX 141931
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
231 PM CDT Fri Aug 14 2026

.KEY MESSAGES...

- There is a significant threat of flash flooding across
  portions of central Illinois overnight into early Saturday
  morning, where thunderstorms track over areas that have
  already seen 4-6 inches of rain since Thursday. Areas north of
  a Havana to Bloomington line are most at risk.

- Some of these storms also have the potential to produce
  damaging winds, mainly after midnight.

- The heat and humidity remain a concern for the weekend, with
  the highest chances of seeing more than a 105 degree heat
  index (40-60%) in areas from Beardstown southeast to Marshall.

&&

.DISCUSSION...
Issued at 231 PM CDT Fri Aug 14 2026

The busy weather trend continues, and focus efforts has
primarily been with the first 24-36 hours of the forecast.


Flooding Concerns:

The earlier rainfall has finally moved out, and the Flood Watch
for east central Illinois was cancelled.

Rainfall amounts of 4 to 6 inches were fairly widespread from
the I-74 corridor and then southward in east central Illinois to
I-70. While the earlier watch from Havana-Bloomington northward
was allowed to expire at 10 am, a new watch has been issued for
this area beginning at 10 pm tonight. The next MCS is expected
to develop across Iowa this evening, as an upper wave moves
across that area, and then move into Illinois shortly after
midnight. HREF precipitable water values over 2.2 inches remain
in place overnight across the northern third of Illinois, and
probabilities of over 2 inches of rain tonight are highest from
Galesburg to Lacon (40-60%). However, its LPMM guidance suggests
3-5 inches are a valid concern, depending on where exactly the
MCS tracks. While the flooding is the main focus with this MCS,
there remains a level 2 severe weather threat with it, primarily
for scattered damaging winds.


Heat Concerns:

Extensive rain today has significantly kept temperatures lower
than earlier projections. While skies are now becoming partly
sunny south of I-72, it is unclear whether enough sunshine will
get heat index readings up to 100 degrees in any of the advisory
area today. The current advisory area is expected to have less
impact from the overnight MCS, and guidance continues to point
toward heat index values 105-110 degrees on Saturday and Sunday.
No changes in the Heat Advisory were made in that area for this
reason. Further north, NBM guidance is also showing similar
heat index for Saturday for all of central Illinois. However,
the lingering effects of the next MCS suggest the guidance is
overdoing projections. HREF probabilities of greater than 105
degree heat index on Saturday are highest from Beardstown
southeast through Taylorville to Marshall (40-60%), and tail off
pretty quickly north of there. Will leave any headline changes
for the overnight forecast cycle, once the MCS shows its hand.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1242 PM CDT Fri Aug 14 2026

Initial convection has largely waned near the central Illinois
terminals, though some isolated storms are still possible for a
couple more hours. Periodic IFR ceilings have been occurring,
especially near KPIA/KBMI, though these should improve through
mid afternoon. More of a focus for widespread ceilings below
2000 feet will be after 06z, primarily KPIA-KBMI, as a large
thunderstorm complex settles into the area. Thunder threats
begin to diminish toward daybreak as the rain gets closer to
KSPI/KDEC. Conditions expected to improve after 15z.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 10 PM CDT this evening through Saturday
morning for ILZ027>031-036>038.
Heat Advisory until 8 PM CDT Sunday for ILZ049>052-061>063-
066>068-071>073.

&&

$$

KEY MESSAGES...Geelhart
DISCUSSION...Geelhart
AVIATION...Geelhart