Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

403
FXUS63 KILX 150519
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1219 AM CDT Sun Jun 15 2025

.KEY MESSAGES...

- A few heavy downpours will persist along and south of I-70
  through early evening. Rainfall rates of 1 to 1.5 inches per
  hour will be likely within the heavier cells.

- The Storm Prediction Center indicates a 15% probability for
  severe weather on Wednesday.

- There is a strong signal for hotter and more humid conditions by
  the end of the week as upper-level heights build over the
  Midwest.

&&

.SHORT TERM...(Tonight through Sunday)
Issued at 245 PM CDT Sat Jun 14 2025

19z/2pm water vapor imagery shows the slow-moving upper low that
has impacted the region for the last couple of days now spinning
over western Kentucky. A broken line of showers/thunder has formed
along its northern flank...along and just south of I-70. Thanks to
copious atmospheric moisture and the slow-movement of the cells,
pockets of heavy rainfall will continue across the SE KILX CWA
through early evening. Rainfall rates of 1-1.50 per hour will
occur with some of the heavier cells. Most CAMs show the showers
dissipating after 03z/10pm, followed by partly cloudy and dry
weather across the board overnight. With partial clearing, light
winds, and ample boundary layer moisture in place...think patchy
fog will once again develop tonight. While the set-up is not
ideal, the GFSLAMP shows widespread minor visby restrictions.
Other CAMs are less bullish, except for the RAP which shows a
dense fog potential from near Quincy southward to west of Saint
Louis. Given what occurred last night, have added patchy fog to
the forecast everywhere after midnight into early Sunday morning.
Once any morning fog dissipates, partly sunny and dry weather is
anticipated for Sunday with high temperatures topping out in the
lower to middle 80s.

Barnes

.LONG TERM...(Monday through Next Saturday)
Issued at 245 PM CDT Sat Jun 14 2025

Warm and humid weather will be on tap for Monday and Tuesday. The
main forcing for precipitation will be another short-wave trough
tracking from the Plains into the Ohio River Valley. While the 12z
models still exhibit a decent amount of spread, consensus suggests
the bulk of the convection will slide across southern Illinois
into southern Indiana/Kentucky Monday afternoon and night. As a
result, have gone with a mostly dry forecast Monday morning...followed
by a 30-40% for showers/thunder along/south of a Rushville to
Paris line during the afternoon and evening. Once this feature
pushes east of the region, short-wave ridging in its wake will
likely inhibit widespread precip development on Tuesday despite an
increasingly warm/unstable environment. Will still hold on to
chance PoPs for Tuesday afternoon...but think the main convective
chances will hold off until later Tuesday night when MCS activity
across the Plains approaches from the west.

The best chance for widespread showers and thunderstorms across
all of central and southeast Illinois will materialize on Wednesday.
Early morning MCS activity will spill into the western KILX CWA
in a weakening state...followed by convective re-development
ahead of an approaching cold front Wednesday afternoon and
evening. SPC has indicated that a 15% chance for severe weather
exists at that time.

Once the cold front passes, a slightly cooler/drier Pacific-
origin airmass will arrive on Thursday. After that, all models
show upper-level ridging building over the Midwest by the end of
the week...with high temperatures perhaps climbing into the lower
90s by next Saturday.

Barnes

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1219 AM CDT Sun Jun 15 2025

A weak high pressure ridge extending southward from the upper
Midwest into western IL will promote light northeasterly winds and
mostly clear skies over west-central IL, while an area of low
clouds persists in east-central IL. As the night progresses, at
least MVFR vsby in thin fog should develop in the west, while MVFR
cigs in low clouds spread through east-central IL. Have started
MVFR conditions 09Z-10Z, but will need to monitor for later
development. VFR conditions should return by 13Z-18Z, with diurnal
cumulus producing sct-bkn sky cover around 4000 ft AGL. Winds NE
3-6 kts overnight, increasing to 6-10 kts by 13Z.

37

&&

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

$$