Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

486
FXUS63 KILX 251105
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
605 AM CDT Wed Mar 25 2026

.KEY MESSAGES...

- There is a Slight Risk (level 2 of 5) for severe weather late
  tomorrow afternoon and evening. The primary hazards will be
  damaging wind gusts and large hail: however, an isolated
  tornado cannot be ruled out.

- Large temperature swings are in store for the remainder of the
  week. Readings will soar to record warm levels in the upper
  80s to near 90 tomorrow afternoon...then will plunge into the
  upper 20s by early Saturday morning.

&&

.DISCUSSION...
Issued at 219 AM CDT Wed Mar 25 2026

A high pressure system is sitting over eastern U.S again today,
bringing gradually increasing temperatures ahead of the low pressure
system Thursday. The warmest highs are on Thursday have a 60-90%
chance of exceeding 80 degrees across the entire forecast area and a
60-80% chance of greater than 85 degrees west of Highway 51, based
off the NBM and HREF probabilities. We are looking at blowing away
the record highs for Thursday, and maybe even record monthly
highs, as the records are around 78-85 degrees. (See climate
section for locations and records)

Thursday`s low pressure system will be accompanied with the warm
front lifting north on Wednesday night and a strong cold frontal
passage Thursday. The warm front could bring some showers and
elevated thunderstorms to central IL late this evening into early
tomorrow morning.

The cold front is bringing strong to severe storms, potential
excessive rainfall, and a sharp drop off in temperatures again. SPC
has maintained central IL a slight risk (level 2 of 5) for severe
weather for this event. All hazards are in play, large (potentially
2+ inch) hail, damaging winds, and a few tornadoes. SPC suggests
that if there is a tornado, there is the chance for it to be of EF2
or greater strength. Timing looks to have the storms entering the
forecast area from the north around 22-00z tomorrow and exiting
to the south by 08-10z Friday morning. The environment, based
off forecast soundings, looks to be primed but will have to
fight a cap initially, but as the front approaches, the cap will
erode. MUCAPE values of 2300-2800 J/kg, with 45-60 knots of
bulk wind shear. Lapse rates sound alarm bells for significant
hail sizes with insane values of 8-8.3 C/km. Then the PWATs,
which are around 1.5- 1.8, and the long skinny CAPE profile
suggest that these storms could be efficient rain producers. The
WPC maintained a marginal risk for excessive rainfall for day
2.

Behind the front, lows Thursday night will dip down into the mid 30s
to low 40s. Highs on Friday won`t be much warmer, with values in the
upper 40s nearing 50. As of now, there is a 50-80% chance that
temperatures will get back above 75 degrees by next Monday.

The Climate Prediction Center 8-14 Day outlook (first week of April)
has 60-80% chance of above normal temperatures over IL with
precipitation trending 40-60% chance above normal. So the mild and
wet/unsettled pattern looks to continue into early April.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 556 AM CDT Wed Mar 25 2026

VFR conditions through the 12z period. Winds will shift to a
more southwestern direction by this afternoon and breezy (10-15
knots, gusting up to 25 knots at times). Some isolated
thunderstorms are possible from 00z-06z this evening. Confidence
in location of these storms is low, so handled it with a PROB30
group during the most likely time for each site.

&&

.CLIMATE...
Issued at 125 AM CDT Wed Mar 25 2026

Forecast temperatures on Thursday may exceed March records in
some areas.

               Mar 26 Record              March Record
Charleston....   84 (1907)          89 (3/24/1929 and 3/22/2026)
Decatur.......   83 (1907)          89 (3/24/1929)
Jacksonville..   83 (1950)          91 (3/21/1907)
Lincoln.......   83 (1991)          86 (3/29/1985 and 3/30/1986)
Normal........   83 (2007)          88 (3/21/1907)
Olney.........   85 (1907)          89 (3/24/1910 and 3/24/1929)
Peoria........   82 (1907/1991)     87 (3/21/1907)
Springfield...   81 (1991)          91 (3/21/1907)
Urbana........   81 (1907)          85 (3/21/1907 and 3/24/1910)

&&

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

&&

$$

KEY MESSAGES...Copple
DISCUSSION...Copple
AVIATION...Copple
CLIMATE...Geelhart