203
FXUS63 KILX 171936
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
236 PM CDT Tue Jun 17 2025

.KEY MESSAGES...

- There is a risk for severe weather across all of central
  Illinois on Wednesday...with the greatest risk (level 3 of 5)
  focused along and southeast of a Champaign to Taylorville line.

- Hot and humid weather will develop by the end of the week. High
  temperatures are progged to rise into the lower to middle 90s
  both Saturday and Sunday, resulting in peak heat index readings
  above 100 degrees.

&&

.DISCUSSION...
Issued at 236 PM CDT Tue Jun 17 2025

...Scattered Thunderstorms This Evening...

A short-wave trough currently over northwest Missouri will trigger
scattered thunderstorms across west-central Illinois this evening.
The 19z/2pm regional radar mosaic shows isolated storms forming
ahead of the wave across far northern Missouri. Most CAMs suggest
this area of convection will increase in areal coverage as it
tracks E/NE into western Illinois late this afternoon and evening.
The HRRR has consistently focused on locations along/west of I-55
between 5pm and 10pm...and this looks reasonable based on the
latest upstream satellite/radar trends. While widespread severe
weather is not likely, a few cells may tap into MLCAPEs of
1500-2000J/kg to produce gusty winds and small hail along with
locally heavy downpours.

...Severe Weather Risk on Wednesday...

As the nocturnal low-level jet strengthens across the Southern
Plains tonight, a prominent outflow boundary extending across
central Kansas will serve as the focus for a cluster of severe
convection. While these storms will follow the boundary and
gradually sink southeastward toward the greatest instability
across the Ozarks into Arkansas, an outflow boundary from the
system will sweep eastward into western Illinois toward dawn
Wednesday...then further east across much of the KILX CWA during
the morning. Scattered non-severe thunderstorms may accompany the
boundary, followed by a lull in precip chances from mid-morning
through early afternoon. After that, we will need to keep a close
eye on both the remnant outflow boundary, as well as the synoptic
cold front as it pushes eastward across the Mississippi River
later in the day. The atmosphere across the region will only be
modestly unstable...with the 12z HREF showing the highest SBCAPEs
in excess of 2500J/kg focusing well east of the I-57 corridor into
the Ohio River Valley. The NAM continues to show 0-6km bulk shear
increasing to 30-40kt...which will be enough to overcome the
limited instability and allow scattered convective development
along both the outflow and cold front. The most favorable
instability/shear/forcing will be in place along/southeast of a
Champaign to Taylorville line where SPC has upgraded the severe
risk to Enhanced (level 3 of 5). The primary storm risks will be
damaging wind gusts greater than 60mph and hail larger than
quarters: however, isolated tornadoes cannot be ruled
out...especially along/south of I-70 where an MCV may provide
enhanced low-level shear. The primary time frame for severe will
be 2pm to 10pm.

...Hot Weather by the End of the Week...

Once the Wednesday system departs, a period of slightly cooler and
drier conditions will be on tap for Thursday before upper heights
rise and temperatures increase markedly. 12z NBM shows a high
probability (70-100% chance) of exceeding 90 degrees across all
of central Illinois next Saturday and Sunday. These temperatures
combined with seasonally high dewpoints in the lower to middle
70s will produce heat index values well over 100 degrees.

Barnes

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1245 PM CDT Tue Jun 17 2025

Robust Cu-field is noted on 1730z/1230pm satellite imagery
along/southeast of a KCMI to KTAZ line. SCT to occasionally BKN
MVFR ceilings are anticipated at both KDEC and KCMI through 20z
before the clouds begin to scatter and/or shift further east.
Further west, FEW-SCT diurnal clouds will prevail for the
remainder of the afternoon. Most CAMs suggest thunderstorm
development west of the Mississippi River later this
afternoon...with the convection lifting E/NE across locations
along/west of the I-55 corridor this evening. Based on latest
RAP/HRRR, have opted to carry a TEMPO group for thunder at
KPIA/KSPI/KBMI from 01z through 03z/04z...before ending the
thunder mention for the night. Latest models indicate MCS activity
will remain well S/SW of central Illinois overnight, but an
outflow boundary from that convection will likely push across the
region Wednesday morning. Scattered convection will be possible
along the boundary, so have introduced a PROB30 group for all
sites between 13z and 18z. Winds will initially be SW at 8-12kt,
then will decrease to less than 10kt by sunset. SW winds will
resume on Wednesday and will become strong/gusty by midday through
the afternoon.

Barnes

&&

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

$$