539
FXUS63 KILX 162255
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
555 PM CDT Wed Sep 16 2026

.KEY MESSAGES...

- A Heat Advisory has been issued for areas south of I-70
  through Thursday, with afternoon heat index values near 105
  degrees. While humidity levels drop off a bit late in the
  week, highs in the 90s are likely to prevail in this area
  through the weekend.

- After heavy rain occurred last night over the northern parts
  of the forecast area, potential exists for additional heavy
  rain tonight. While the greatest threat is closer to I-80, a
  Flood Watch has been issued for Knox, Stark and Marshall
  Counties.

&&

.DISCUSSION...
Issued at 205 PM CDT Wed Sep 16 2026

Latest surface map shows the front draped just north of I-70. A
large temperature range is in place over the forecast area early
this afternoon, ranging from the lower 70s near Galesburg, to
the mid 90s south of I-70. Convection has recently been firing
south of I-70, along an axis of SBCAPE over 3000 J/kg, while
scattered showers persist over the northern third of the
forecast area.

Not a lot of movement is expected with the front the next few
days, remaining draped over central Illinois courtesy of a large
upper high over the southeast U.S. Gulf moisture has been
feeding into the mid Mississippi Valley due to the high`s
circulation, and unseasonably high precipitable water values
over 2 inches will remain pooled just north of the boundary. Two
consequences of this pattern: 1) Unseasonably hot weather with
highs in the 90s (mainly south of I-70) continuing into the
weekend, and 2) potential for additional heavy rain across
northern Illinois tonight.

- Heat Concerns: A Heat Advisory has been issued for areas
  south of I-70 through Thursday. Dew points in the lower 70s
  will result in heat indices approaching 105 degrees both this
  afternoon and Thursday afternoon. As the boundary slips a
  little further south Thursday night, slightly lower
  temperatures and dew points should keep the heat index just
  under 100 degrees on Friday.

- Rain Concerns: Morning model suite has been advertising development
  of an MCS across southeast Iowa later this evening, tracking
  eastward across northern Illinois overnight into early
  Thursday. With the excessive precipitable water values and
  training storms, potential for areas of flash flooding is
  high. Heavy rain last night of 2-4 inches fell from the
  southeast tip of Iowa to north of Peoria. While the core of
  the heaviest rain tonight is expected closer to I-80, a number
  of CAM`s do show storms potentially tracking as far south as
  I-74. HREF and REFS LPMM both suggest amounts around 2 inches
  from Galesburg to Lacon are not out of the question. Thus, a
  Flood Watch has been issued for Knox, Stark and Marshall
  Counties until 10 am Thursday.

Going further out in time, while the front begins lifting back
north as a warm front Friday night, the boundary never fully
exits the region until early next week. At that point, a strong
shortwave over the northern Plains and upper Mississippi Valley
should finally kick the front eastward. Until then, rain chances
will persist, with the highest chances from Saturday night into
Sunday night.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 555 PM CDT Wed Sep 16 2026

A disturbance will bring scattered TSRA to parts of central IL
late tonight and Thursday morning, most favored north of I-74.
Have a PROB30 group to account for this at KPIA-KBMI-KCMI. Aside
from storms, MVFR ceilings are likely to impact these sites
after 06z. Models show a sharp cutoff to the southern edge of
the MVFR ceilings north of KSPI-KDEC, so kept the mention out of
their TAFs, and will monitor trends this evening. A frontal
boundary wavering across the region will result in light and
variable winds through the period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 10 PM CDT this evening through Thursday
morning for ILZ027-028-030.
Heat Advisory until 7 PM CDT Thursday for ILZ066>068-071>073.

&&

$$

KEY MESSAGES...Geelhart
DISCUSSION...Geelhart
AVIATION...25