815
FXUS63 KILX 272343
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
643 PM CDT Fri Jun 27 2025

.KEY MESSAGES...

- A broken band of thunderstorms will move across southeast IL
  through early evening (40-60% chance). A few storms could be
  strong to severe with wind gusts 50 to 60 mph along with locally
  heavy rains up to 1 inch in less than an hour. Additional
  showers and thunderstorms are likely Sunday into Monday (50-80%
  chance).

- Very warm and humid conditions persist through Monday, with peak
  heat indices in the mid to upper 90s this weekend and lower 90s
  on Monday afternoon. Temperatures and humidity levels return to
  seasonable values during the middle of next week, with highs in
  the mid/upper 80s and lows in the 60s.

&&

.DISCUSSION...
Issued at 245 PM CDT Fri Jun 27 2025

A broken band of convection was southeast of a Danville to
Shelbyville line and back west to the St Louis area, and
convection was about as far southeast as I-70 at 230 pm. A few
cells have been strong to severe with wind gust of 63 mph at MTO
at 107 pm and trees blown down on wires a mile west of Mattoon at
1 pm. This convection was tracking ENE between 15-25 mph and along
an outflow boundary. Very unstable airmass with SB CAPES near 3000
j/kg in southeast IL with steeper low level lapse rates, though
very weak bulk wind shear. Heat waves continues in southeast IL
today. Heat indices southeast of this line of convection were
around 100 degrees with Lawrenceville airport reaching 102F (air
temp 97F). SPC day1 outlook updated to have marginal risk of
severe wind gusts over eastern IL along and ahead of this line of
storms through early evening. The heat advisory in southeast IL
goes until 7 pm today, though we will likely be removing several
counties as convection moves through and cools temperatures, with
far southeast CWA likely staying in it a few more hours. Latest
CAMs continue chances of convection in southeast IL this evening
then most areas fairly dry overnight with some patchy fog possible
later tonight especially northern/nw CWA. Lows overnight in the
upper 60s north of I-72 and lower 70s from I-72 south. Lows in the
mid 60s from Galesburg to Lacon north.

An unstable air mass lingers over southeast IL on Saturday keeping
20-30% chance of convection while central IL should be drier with
more sun. Highs near 90F on Sat with afternoon heat indices in the
mid to upper 90s with dewpoints around 70F to lower 70s so still
muggy. Fair wx expected over CWA Sat night, then chance of
convection increases from sw to ne during the day Sunday as deeper
tropical moisture advected northward with 50-70% pops Sunday
afternoon/evening. Highs Sunday in the mid to upper 80s, warmest
from I-74 north and heat indices peaking back in the mid to upper
90s Sunday afternoon. SPC day3 has marginal risk of severe storms
later Sunday afternoon into Sunday night over nw IL (nw of the IL
river) for damaging winds as cold front moves se into nw IL late
Sunday night. WPC has marginal risk of excessive rainfall over
much of area Sunday afternoon and Sunday night in tropical
airmass. The cold front to move se through rest of CWA on Monday
likely bringing showers and chance of thunderstorms and could see
a few stronger storms by Monday afternoon in southeast IL. Highs
Monday in the mid 80s and still humid with heat indices in the
lower 90s Mon afternoon. We have 20-40% chance of convection in
southeast IL Mon evening then dry weather returns across area for
Tue into Wed night. Temps and humidity levels return to normal
levels Tue/Wed with highs in the mid to upper 80s and dewpoints in
the 60s.

Blended models have small pops of convection on Thu with northern
stream short wave tracking se over the area. The strong upper
level ridge and heat dome will be sw of central IL much of next
work week keeping oppressive heat and humidity sw of area.

07

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 637 PM CDT Fri Jun 27 2025

The wave of scattered thunderstorms that generated heavy rain and
frequent lightning at SPI and CMI continues gradually weakening,
while another wave of showers and a few storms has developed on
an outflow boundary sent north by those original storms. This
wave, focused roughly along the IL River, will (based on
radar/satellite trends and the latest HRRR) be too close for
comfort at PIA and BMI where PROB30 groups were added. However,
beyond roughly 02z/9pm storms should abate with waning diurnally
driven instability. Winds will diminish overnight, and with only a
few mid-high clouds radiational cooling may be sufficient for
some shallow ground fog. Brief visibility reductions into the IFR
category will be possible (20-30% chance, per HREF), but MVFR was
left in the TAFs for now given higher confidence (30-50% chance),
especially at PIA.

Bumgardner

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT this evening for ILZ068-072-073.

&&

$$