Normal, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

431
FXUS63 KILX 182343
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
643 PM CDT Thu Jun 18 2026

.KEY MESSAGES...

- Confidence for heavy rainfall on Sunday is increasing as the
  latest NBM indicates a 30-40% chance of greater than 3 inches
  along and north of a Quincy to Tuscola line.

- The severe weather risk for Sunday remains low, however some
  guidance is suggesting greater than 15% probabilities from the
  Ozarks eastward into the Ohio River Valley.

&&

.DISCUSSION...
Issued at 229 PM CDT Thu Jun 18 2026

**** Heavy Rainfall on Sunday ****

Unseasonably deep upper troughing over Canada will continue to
suppress the polar jet stream southward into the northern CONUS
over the next week...resulting in below normal temperatures and
periodic rain chances. Numerous waves embedded within the
active jet stream will traverse the region, with the most
significant wave slated to approach from the west Saturday night
into Sunday.

The airmass ahead of the short-wave trough will initially be
dry/stable: however, increasing S/SW flow courtesy of an 850mb
jet streak progged to increase to 50-55kt will transport copious
moisture northward into central Illinois. The 12z Jun 18 NAM
indicates surface dewpoints climbing into the upper 60s to
around 70 degrees by Sunday afternoon...with precipitable water
values reaching 2.00-2.25.

Synoptic models are in good agreement concerning the track/strength
of the upper wave and the overall water content of the atmosphere,
but vary with the track of their respective surface lows. The
GFS is the weakest and furthest south with the low pushing into
the heart of central Illinois by 00z Mon. Meanwhile both the
ECMWF and NAM are stronger/further north into northern Illinois.
The exact track of the low will determine the axis of heaviest
rainfall, as the most persistent rains will occur north of the
track. The 12z NBM indicates a high probability (70-80% chance)
of greater than 1 inch across all of central and southeast
Illinois from late Saturday night through Sunday night...and a
30-40% of more than 3 inches along/north of a Quincy to Tuscola
line. Will need to keep a close eye on surface low forecasts
over the next day or two, because rainfall of that magnitude
could potentially lead to flooding across the northern half of
the KILX CWA. If the further north ECMWF/NAM verify, the
heaviest rainfall axis would be shifted further north into
northern Illinois/southern Wisconsin.

**** Severe Weather Potential on Sunday ****

The Storm Prediction Center (SPC) has not yet highlighted any
severe weather risk for Sunday, but this will likely change with
upcoming updates due to growing confidence for convection from
the Ozarks into the Ohio River Valley Sunday afternoon and
evening. As discussed above, the exact track of the surface low
will be key...as it will also determine the areal extent of the
severe risk. Machine learning algorithms have coalesced around
a solution focusing 15-30% probabilities from central/southern
Missouri across the southern portions of Illinois and Indiana.
This would include the southern KILX CWA mainly along/south of
I-70. If however the further north low track pans out, the risk
area would shift northward to include more of central Illinois.
At this time, will forecast widespread showers and thunderstorms
on Sunday with locally heavy rainfall as the main risk. Given
strong 850mb winds and 0-6km shear of 40kt or greater, even weak
instability may be enough to generate strong to possibly severe
convection across portions of the area. Stay tuned to later
forecasts for additional details.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 643 PM CDT Thu Jun 18 2026

VFR conditions are expected through the TAF period. Northwest winds
will become light and variable overnight, returning to the west-
northwest by mid to late morning with speeds below 12 kts.

&&

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

&&

$$

KEY MESSAGES...Barnes
DISCUSSION...Barnes
AVIATION...NMA