867
FXUS63 KILX 081840
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
140 PM CDT Tue Jul 8 2025

.KEY MESSAGES...

- There will be daily chances (20-50% coverage) for showers and
  storms through the remainder of the week and into the weekend.
  Storms will generally be favored during the afternoon and
  evening hours, except for Friday night as a warm front lifts
  across the region. There is a marginal risk (level 1 of 5) for
  severe storms this afternoon and evening.

- Seasonable heat and humidity will remain in place the remainder
  of the week into this weekend with afternoon highs generally
  in the mid to upper 80s and dew points in the 70s. A few spots
  may tag 90 degrees Friday.

&&

.DISCUSSION...
Issued at 135 PM CDT Tue Jul 8 2025

This afternoon, water vapor imagery shows a shortwave trough
digging across the Upper Midwest and into the western Great Lakes
region while another more subtle shortwave trough is digging
across central Missouri. Ahead of these features, broad ascent
should be able to tap into an unstable and uncapped air mass in
place across central Illinois allowing for thunderstorms to
develop. RAP suggests around 2000 J/kg MLCAPE will be present
across much of central Illinois this afternoon along with minimal
MLCin. Despite the mid level features, deep layer shear is
expected to be weak, around 20 kt or less which will keep a more
organized severe threat in check. As such, a pulse severe threat
with isolated, damaging downburst winds will be the primary
concern this afternoon and evening. In addition, 12Z HREF LPMM
continues to suggest that some localized pockets of very heavy
rain of 3-5 inches will be possible.

Wednesday and Thursday will see much of the same across central
Illinois with seasonably warm and humid conditions along with
weakly forced convective chances which will peak during the
afternoon and evening hours. GFS suggests both days will see
moderate instability with MLCAPE values around 1500 J/kg and weak
deep layer shear of 15-20 kt or less. As such, disorganized and
scattered convection with a pulse severe wind threat will again be
concerns. Slow storm motions could lead to some additional
isolated pockets of very heavy rain. That being said, given the
scattered nature of storms it`s important to remember that many
areas will not see rain.

Friday into Saturday, a more robust shortwave trough is progged to
dig across the northern Great Plains into the Upper Midwest with a
surface low deepening over the Upper Midwest Friday evening. A
warm front will lift across central Illinois as a result and
Friday looks to be the best day to see some locations tag 90
degrees again. Shear and instability parameters look to be more
supportive of severe weather Friday. GFS advertises around 2500
J/kg MLCAPE with modest capping (40-50 J/kg) and around 30 kt of
0-6km shear. This would support some scattered strong to severe
storms during the afternoon, but a greater severe threat may
materialize Friday evening as a low level jet develops resulting
in upscale growth of storms as they track east along the warm
front/instability gradient. There remains a high degree of
uncertainty with placement and timing of these storms with the
latest GFS a couple hundred miles further east compared to
yesterday`s run. Additional storms will be possible Saturday
associated with the remnant outflow or trailing cold front,
although the faster GFS suggests the threat Saturday may set up
just to our east. As timing details are yet to be resolved, Friday
and Saturday will bear close watching in the meantime.

Frontal boundary will stall near the Ohio Valley late this weekend
with Sunday having the best chance to stay dry within the post
frontal air mass. Highs will be slightly lower Sunday, topping out
in the lower to mid 80s. The frontal boundary lifts back north
early next week with daily chances for precip returning as the hot
and humid conditions overspread central Illinois once again.

Deubelbeiss

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1222 PM CDT Tue Jul 8 2025

For the most part, ceilings and visibilities should remain VFR, but
there are storms expected to move through this afternoon and
evening. When a storm passes over a TAF site, visibilities could
drop down to 2SM due to the expected heavy rain. Some of these
storms could have severe winds (up to 60 mph). The storms should be
out of the western sites by 01z and out of CMI by 04z.

Overnight, winds will be nearly calm and shifting from southwesterly
to northwesterly.

Copple

&&

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

$$