950
FXUS63 KILX 152353
AFDILX

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

.KEY MESSAGES...

- Strong thunderstorms will develop across parts of central
  Illinois on Wednesday. The highest probability (15-30% chance)
  for severe weather will focus along and north of a Macomb to
  Bloomington line.

- After mostly dry conditions Thursday night into Friday, rain
  chances will once again increase over the weekend.

- Heat and humidity will build next week...with early projections
  suggesting heat index values climbing well above 100 degrees by
  next Tuesday.

&&

.DISCUSSION...
Issued at 223 PM CDT Tue Jul 15 2025

...Severe Weather Risk on Wednesday...

As a frontal boundary currently draped across the Upper Midwest
into the Plains sags southeastward, it will interact with a highly
unstable and weakly sheared environment to trigger scattered
strong to severe thunderstorms across mainly north-central
Illinois Wednesday afternoon and evening. Given surface dewpoints
rising into the middle to perhaps upper 70s, HREF mean SBCAPEs
reach 2500-3000J/kg by peak heating. Deep-layer wind shear has
been absent for the past couple of days: however, as a short-wave
trough ejecting E/NE out of the Rockies approaches, 0-6km bulk
shear is progged to increase to 20-30kt...with even higher values
in excess of 40kt focused further north across central/southern
Wisconsin. 12z HREF shows a high probability (40-60% chance) of
SBCAPEs exceeding 2000J/kg and 0-6km greater than 20kt along/north
of a Macomb to Bloomington line where SPC has highlighted a Slight
Risk for severe. CAMs still exhibit some timing and areal coverage
differences: however, based on latest water vapor imagery showing
the position of the short-wave, think the earlier models such as
the HRRR and NSSL WRF are more on target rather than the slower
NAM. As such, think a broken line of thunderstorms will develop
ahead of the slowly approaching cold front across eastern
Iowa/northwestern Illinois toward midday....then will advance
eastward across locations mainly along/north of I-72 during the
afternoon. Given severe weather parameters, think damaging wind
gusts in excess of 60mph will be the primary severe weather risk.
Further north where shear will be stronger, the chances for large
hail and a few tornadoes increase across far northern Illinois
into southern Wisconsin.

...Additional Storm Chances over the Weekend...

The cold front will settle southward through central Illinois on
Thursday...triggering additional showers and thunderstorms. Based
on the position of the frontal boundary, the greatest rain chances
on Thursday will materialize along/south of I-72 during the
afternoon, although the chance for severe weather will remain low.

The front will sink south of the region Thursday night into
Friday, setting up a period of slightly cooler/drier weather.
After that, the boundary will lift back northward and become
stationary within the quasi-zonal upper flow pattern over the
weekend. As individual short-wave troughs track eastward through
the zonal flow and interact with the boundary, scattered
thunderstorms will occur from time to time Friday night through
Monday. It is still too early to pinpoint any severe weather risks
during that time: however, it appears likely that a few locations
will see locally heavy rainfall. While the NBM is forecasting
widespread copious rainfall amounts, think this may be a bit
overdone due to questions regarding timing of the waves and exact
areal coverage of the corresponding convection. The 00z Jul 15
LREF seems to have a much more reasonable handle on the potential
rainfall...showing a 70-100% chance of greater than 1 inch tonight
through next Tuesday...and a 30-50% chance of more than 2 inches.
After that, ridging will build over the Midwest and summertime
heat and humidity will return in earnest next week. The latest NBM
guidance suggests high temperatures reaching the lower 90s and
heat index values exceeding 100 degrees across the board by next
Tuesday.

Barnes

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 645 PM CDT Tue Jul 15 2025

Scattered showers and thunderstorms will continue until around
sunset, with a general diminishing trend, although it appears only
KSPI will be affected, while KBMI and KDEC may have vicinity
storms. VFR conditions will be prevalent through most of the
night, until near sunrise, when vsby reductions due to fog will be
possible. As fog lifts in the morning, a period of MVFR cigs will
be around 15Z-18Z. Finally, thunderstorms are expected to move
into the area Wednesday afternoon, especially for northern
portions of the area, and have included TEMPO for tsra at KPIA and
KBMI, but PROB30 for KSPI, KDEC, and KCMI. Winds SSE 3-5 kts
overnight, shifting to SW around 10 kts by 15Z.

37

&&

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

$$