Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

802
FXUS63 KILX 021558
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
1058 AM CDT Wed Apr 2 2025

.KEY MESSAGES...

- A significant severe weather event will unfold later today. The
  highest probabilities (greater than 10% chance) for tornadoes
  continue to be focused along/southeast of a Champaign to
  Taylorville line this afternoon.

- Very strong southerly winds will develop today...with gusts
  reaching as high as 50-55mph along the I-57 corridor.

- Multiple rounds of showers and thunderstorms will lead to a risk
  for excessive rainfall and flooding issues along and south of
  I-70...where a Flood Watch is in effect from this afternoon
  through Sunday morning.

&&

.UPDATE...
Issued at 1058 AM CDT Wed Apr 2 2025

A warm front associated with a powerful low to the northwest has
surged northward through the area, with RAP-based mesoanalysis
indicating 1000-1500 J/kg CAPE in the warm sector developing
across the area east of I-55. Moving into this area has been a
cluster of thunderstorms containing damaging winds. While this
cluster should move off toward northeast IL by noon, additional
thunderstorms will develop eastward from current activity in
Missouri, as well as spread northeastward into areas mainly east
of I-55. An Enhanced Risk for severe thunderstorms/tornadoes
continues, with a Moderate Risk from I-70 southward where eventual
destabilization should be maximized by late this afternoon. At
this time, there is fairly good high-resolution model guidance
suggesting severe storms pass I-57 by 7 PM and Lawrenceville by 9
PM. General winds will be strong and gusty as well, with 45-55 mph
gusts expected to spread across the entire area (strongest in
east-central IL) by afternoon, and a Wind Advisory is in effect.
Updates this morning have been minimal as PoPs/Thunderstorm
chances have been right on track. Temperatures and winds have been
affected in and behind the cluster of storms that moved through
the I-55 corridor, and continue to make short term adjustments for
cooler temperatures and disruptions to the south/southeast winds
in this area.

37

&&

.DISCUSSION...
Issued at 354 AM CDT Wed Apr 2 2025

...Severe Weather Today...

08z/3am surface analysis shows a warm front extending from Kansas
to western Tennessee. Clusters of non-severe elevated convection
have developed well north of the boundary across central Illinois.
These storms will continue to shift steadily northward and will be
mostly N/NE of the KILX CWA by daybreak. Meanwhile further west, a
more significant line of convection has formed along a cold front
from eastern Kansas into Oklahoma. This line is expected to
continue tracking E/NE into the Illinois River Valley after 8am.
Forecast soundings suggest the convection will be elevated by the
time it arrives here: however, gusty winds and hail will be likely
with the strongest cells. Based on 06z HRRR/RAP data, it appears
the line will shift eastward to the I-55 corridor and weaken
somewhat by late morning...before renewed convection fires along
the leading edge/outflow by mid-afternoon. As has been seen by
the past several model runs, the most significant severe weather
risk will likely unfold east of the I-55 corridor this afternoon
as the cells become surface-based and interact with a moderately
unstable and highly sheared environment. While wind profiles will
become more unidirectional after the warm front lifts into the
southern Great Lakes, a very strong jet streak aloft will
contribute to impressive speed shear. As a result, think initial
storm mode will be supercellular...with a resulting large hail and
tornado risk. The cells will rapidly grow upscale into a line as
they push across the I-57 corridor...with a continued threat of
damaging wind gusts and embedded tornadoes. Some of the tornadoes
could potentially be strong, with the latest SPC outlook
highlighting a 10% or greater chance for an EF-2 or stronger
tornado along/southeast of a Champaign to Taylorville line. The
convective line will then rapidly push into Indiana and exit the
KILX CWA by early evening.

...Strong Winds Today...

A Wind Advisory remains in effect for all of central Illinois this
afternoon and for locations along/east of I-55 into the evening.
Wind gusts have consistently been in the 25-35mph range since last
evening and will remain at this magnitude through mid-morning when
forecast soundings indicate the low-level inversion will break
and higher momentum air from aloft will mix to the surface. Latest
regional VAD wind profilers show the 850mb jet streak has
increased to 65-70kt from the Ozarks northeastward into central
Illinois. The 00z NAM shows this powerful jet translating
northeastward today, and as the inversion erodes in the warm
sector...very strong winds will reach the surface. Based on the
expected location of the jet core, think wind gusts will be
maximized along the I-57 corridor from mid-morning through mid-
afternoon. HRRR has consistently shown gusts in the 45-50mph range
across this area, but would not be surprised to see a few gusts
perhaps as high as 60mph. Considered upgrading locations
along/east of I-57 to a High Wind Warning, but opted instead to
maintain the current Advisory and highlight peak wind gusts as
high as 55mph.

 ...Flood Risk Across Southeast Illinois...

The cold front will settle southward and stall across the Ohio
River Valley tonight as it becomes parallel to the upper level
flow. The boundary will remain quasi-stationary from tonight
through Saturday night before a pattern change pushes it well
south of the region by Sunday. Individual short-wave troughs
interacting with the boundary in conjunction with the nocturnal
low-level jet will lead to numerous rounds of showers and
thunderstorms focused across the Ohio River Valley. While the GFS
tends to keep the front locked in place and produces repeated
rains over the same locations, the ECMWF indicates the boundary
will waver north/south, resulting in rainfall more evenly
distributed. Whichever solution ultimately verifies, consensus
suggests an extreme rainfall event across the Ohio River Valley.
Current WPC QPF forecast keeps the most extreme rainfall amounts
mostly south of the KILX CWA closer to the Ohio River:however,
7-day amounts potentially greater than 5 inches come as far north
as a Danville to Taylorville line. Storm total rainfall steadily
decreases further N/NW, with 7-day accumulations of just 1-2
inches across the Illinois River Valley. Due to high confidence
for excessive rainfall and flooding, a Flood Watch will remain in
effect for locations along/south of I-70 from this afternoon
through Sunday morning.

Barnes

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 602 AM CDT Wed Apr 2 2025

Line of convection seen on 1030z/530am radar mosaic extending from
northern Missouri to eastern Kansas will track northeastward into
central Illinois this morning. Based on radar timing tools and the
latest HRRR/RAP output, have introduced predominant thunder at
KPIA/KSPI by 15z...then further east to KCMI by 17z. Once the
initial line passes, additional convection will re-develop along
the leading edge/outflow...leading to several hours of potential
thunder at the eastern terminals. Have therefore kept thunder
mention going at KDEC/KCMI until 23z. Once the convection departs,
low clouds will break up...leading to a partly to mostly clear
night. Winds will initially be E/SE at 15-20kt early this morning,
then will veer to S and increase markedly by mid to late morning.
Gusts will reach 35-40kt at most sites...and could potentially be
as high as 40-45kt at KDEC/KCMI. The strong winds will slowly
decrease toward sunset, then will drop to 10-15kt after 04z/05z.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 PM CDT this evening for ILZ027>031-036-037-
040>042-047>051.

Wind Advisory until midnight CDT tonight for ILZ038-043>046-
052>057-061>063-066>068-071>073.

Flood Watch through Sunday morning for ILZ062-063-066>068-
071>073.

&&

$$