Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

378
FXUS63 KILX 231850
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1250 PM CST Tue Dec 23 2025

.KEY MESSAGES...

- A semi-stationary frontal boundary will stall over the region
  resulting in a wide range of temps that span from the 40s north
  to 60s south Wednesday and Thursday. NBM shows a greater than
  90% probability for the entire area to reach at least 50 degrees
  Friday and Saturday.

- A pair of waves will result in light rain or drizzle Wednesday
  and again later Thursday. Precip amounts will be light with only
  a 20-30% chance to exceed 0.10 inches of rain each event.

&&

.DISCUSSION...
Issued at 1241 PM CST Tue Dec 23 2025

This afternoon, low pressure is tracking east across Ontario into
Quebec with the tail end of a cold front / col area pushing across
central Illinois. Weak forcing with central Illinois well
displaced from the main upper wave and limited moisture (PWats 0.6
in or less) should keep central Illinois primarily dry during
frontal passage. The exception will be in SE IL near the I-70
corridor where forcing may be just sufficient to squeeze out some
patchy drizzle or very light rain from the low stratus currently
in place.

Frontal boundary is progged to stall along the Ohio Valley and
then lift back north into central Illinois Wednesday into
Thursday as another shortwave trough traverses the region. A tight
temperature gradient will be over central Illinois as a result
with upper 40s for highs in the northern CWA and low to mid 60s in
the south. Frontal position near the I-72 corridor is
contributing to an increased amount of uncertainty in specifics on
temps through the latter half of the week. NBM 25th-75th
percentile MaxT spread is roughly 6-7 degrees across the heart of
the CWA Wednesday owing to uncertainty in the placement of the
front. This increases to 7-9 degrees Thursday and 8-10 degrees
Friday. In general, 40s and 50s are expected north of the front
with 60s south.

The frontal position will also determine where PoPs and cloud
cover are maximized. Isentropic ascent along the 295K and 300K
surfaces will increase both Wednesday afternoon and Thursday night
in response to passing shortwave troughs with light precip
favored just north of the frontal boundary both periods. Precip
amounts will be light both days with the probability of reaching
or exceeding a tenth of an inch of rain only 20-30 percent
along/north of I-74.

A pattern change is expected by late in the weekend as a strong
shortwave digs across the Great Lakes Sunday which will finally
help push our quasi-stationary boundary out of the area into the
deep south. Highs in the 60s Saturday will be replaced by highs
in the 30s and 40s Sunday and 20s Monday. Overnight lows will dip
back into the teens for much of the area Sunday night and Monday
night.

Deubelbeiss

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1120 AM CST Tue Dec 23 2025

VFR conditions last through the 18z period. Nearing the end of the
period, a cloud deck of lowered ceilings will start to move into
the SPI area, spilling northeast. Left out the MVFR ceilings but
indicated lowered ceilings moving in by dropping the ceilings to
BKN035 at SPI by 16z.

Winds around 10 knots will shift from the north to the southeast
through the period. Speeds will drop down near 5 knots overnight,
before increasing back to ~10 knots tomorrow morning.

Copple

&&

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

$$