995
FXUS63 KILX 151755
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1255 PM CDT Tue Jul 15 2025

.KEY MESSAGES...

- Increasing warmth and humidity will bring heat indices into the
  triple digits Wednesday afternoon. This will increase the risk
  of heat illness for vulnerable populations.

- Daily chances (30-60%) for thunderstorms exists today through
  the weekend. There is a slight risk for severe weather and
  excessive rainfall Wednesday.

&&

.DISCUSSION...
Issued at 219 AM CDT Tue Jul 15 2025

Today, the stationary front starts to shift northward, bringing in
more showers and thunderstorms. The storms will be of the typical
summertime airmass variety. They have already been popping up down
south of I-70 this morning. They will pop here and there for much of
the day. Any storms that do occur could produce decent rainfall
locally. A quick inch in rainfall would not be surprising. However,
location of where that rainfall will occur is uncertain due to the
scattered nature of the activity. Forecast soundings in southeastern
IL show a long, skinny CAPE profile, slow storm motions (~20 knots),
and PWATs around 2-2.3 inches, which would support very heavy
rainfall and localized flooding risk. SBCAPE values are around 2000-
3000 J/kg, with no CIN and low shear. Severe threat is not expected,
but strong wind gusts (up to 30-40 mph) would be possible within any
stronger downbursts.

Tomorrow (Wednesday), there is a slight risk for severe weather that
encompasses the northwestern corner of our forecast area and a
marginal risk that extends down to I-70. A shortwave is expected to
pulse across northern/central IL. Currently, this is looking to be a
late afternoon into evening event. The models are showing PWATs
around 2 inches, astronomical SBCAPE values (40-60% chance of >3500
J/kg), MLCAPE around 2000-3000 J/kg, and DCAPE around 1000-1400
J/kg. Concerns will be with a 2% tornado risk, and 15% wind risk.
There is some indication of bowing segments along a linear system.
Slow storm motions are shown on forecast soundings and potential for
training, so another flooding threat is being closely monitored. WPC
has added a slight risk ERO for the IL River and north.

Beyond Wednesday, periodic chances for showers and thunderstorms
exist into the weekend. WPC is already showing a slight risk of
excessive rainfall on day 5 (Saturday) for the I-74 corridor and
north.

Temperature wise this week. The hottest day of the week is
Wednesday, with the WAA in place pulling much more humid and hot
air. We can see heat indices of 100-105 degrees ahead of the
shortwave`s arrival. It will cool off ever so slightly on Thursday
and Friday. Then heat indices get back near or just above 100 again
for the weekend.

Copple

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1255 PM CDT Tue Jul 15 2025

1740z/1240pm radar shows widely scattered convection developing
across central Illinois...with the highest concentration focusing
along/east of I-57. Based on radar trends and latest RAP/HRRR
output, have opted to maintain PROB30 for thunder at all sites
except KPIA through 23z/00z. After that, storm coverage will
steadily decrease through the evening, followed by dry conditions
overnight into Wednesday morning. Given ample boundary layer
moisture and corresponding low LCLs, cloud bases were 1500-2500ft
upon initial development this morning. Bases have mostly improved
to low VFR as of midday, with MVFR lingering at just KDEC. Since
the atmosphere will be unchanged, think the same process will
unfold Wednesday morning, with SCT-BKN clouds at around 2500ft
forming by 15z. Any scattered convection will hold off until
afternoon. Winds will initially be S/SE at less than 10kt this
afternoon, then will veer to SW and increase to around 10kt
Wednesday morning.

Barnes

&&

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

$$