486
FXUS63 KILX 251947
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
247 PM CDT Wed Jun 25 2025

.KEY MESSAGES...

- Heat wave that started this past weekend continues into this
  weekend over central and southeast IL. The highest heat index
  readings of 100 to 108 degrees will occur this afternoon and
  Thursday afternoon, but will remain in the upper 90s to around
  100 degrees through Sunday afternoon.

- Thunderstorm chances will be fairly isolated into mid evening
  and again Thursday afternoon and evening (20-40% areal
  coverage), but will increase markedly by Friday into Saturday
  and again Monday as a cold front moves into Illinois.

&&

.DISCUSSION...
Issued at 245 PM CDT Wed Jun 25 2025

Isolated to scattered convection had fired up over central IL
past few hours and currently focused north of I-70 and south of
I-80. A large outflow boundary was spreading southward from
Lincoln area into nearby counties and seeing a few isolated cells
developing along it between Bloomington and Farmer City. Very
unstable air mass in place with MLCapes 2500-3000 j/kg and SB
CAPES of 3500-4500 j/kg and topping 5000 j/kg over parts of
central and southeast Iowa. Wind shear is weak over IL with Bulk
Shear of 30 kts or higher north of IL over WI. Main synoptic
frontal boundary was in far northeast IL into southern MN and
extending to 1014 mb low pressure in se SD. Temps were in the low
to mid 90s outside of thunderstorms (except lower 80s at rain
cooled Galesburg and Lacon) while heat indices were 99-106F at 230
pm. The cells are pulsey type and could briefly become strong to
potentially severe for wind gusts along with locally heavy rains
of 1-2 inches per hour (tropical air mass has PW values of 1.8-2
inches). SPC day1 outlook has marginal risk of severe storms over
central and northern IL from Macomb to Decatur to Terre Haute
northward until sunset.

The frontal boundary should mostly stay north of IL through Thu
night as low pressure moves east of Green Bay by sunrise Fri. The
better chances of convection will be focused north of CWA along
with stronger risk of severe storms. Our weather on Thursday
should be similar to today with isolated to scattered convection
Thu afternoon into Thu evening. SPC Day2 has marginal risk of
severe storms for damaging winds from Quincy to Lincoln to
Danville north on Thu afternoon/early Thu evening along with
locally heavy rains possible again. Lows overnight in the mid 70s
with highs Thu similar to today`s in the low to mid 90s. This
combined with dewpoints in the low to mid 70s to give peak heat
indices of 100-108F again Thu afternoon. We continued the heat
advisory for CWA (except far northern 3 counties of Knox, Stark
and Marshall) through 7 pm Thu and may need to be extended into
Friday for southeast IL counties.

Cold front to push se into IL river valley Friday morning and a
boundary pushing into southeast IL by Fri evening. This will bring
increased chances of convection Fri especially Fri afternoon.
Highs Fri in the mid to upper 80s over the IL river valley and
lower 90s in eastern IL and possibly near 95F in Lawrenceville and
heat indices reaching near 100F or higher. Areas from Champaign
to Shelbyville se may need to have heat advisory extended through
Fri afternoon and will depend on evolution of convection with
frontal boundary movement.

Still a good chance of convection on Saturday though best chances
of convection starting to shift into southeast IL by late Saturday
and Sat night. Highs Sat in the upper 80s to around 90F with
afternoon heat indices in the mid 90s to near 100F. Tropical air
mass to linger over central/se IL this weekend along with
continued chances of convection especially during afternoon and
early evening hours. Highs in the lower 90s Sunday with afternoon
heat indices around 100F or higher. So we will likely need to
monitor possible heat advisory headline or a special weather
statement.

A stronger cold front to push se into IL on Monday and likely
brings convection chances along with the risk of strong to severe
storms. Convection chances shift southeast on Tue with 20-30% pops
from I-72 south, chance pops se of I-70. Drier and a bit cooler
and less humid conditions Tue night and Wed as temps and humidity
levels return to more normal early summer levels.

07

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1245 PM CDT Wed Jun 25 2025

Isolated to scattered showers and thunderstorms have developed in
past hour over central IL, especially from I-55 east and tracking
slowly ENE in a very unstable tropical air mass with SB CAPES of
3500-4500 j/kg, and PW values of 1.8-1.9 inches. Continued prob30
of TS this afternoon and early evening until 00-01Z for MVFR
conditions possible (and possibly lower vsby conditions if heavier
rains move in. Could also be gusty winds over 30 kts with any
thunderstorms this afternoon. Otherwise fairly light SSW to SW
gradient winds less than 10 kts next 24 hours over central IL
airports. Diurnally driven cumulus cloud field with scattered to
broken bases of 3-5k ft to diminish after sunset and redevelop by
late Thu morning, with isolated convection again possible Thu
afternoon.

07

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT Thursday for ILZ029-031-036>038-
040>057-061>063-066>068-071>073.

&&

$$