902
FXUS63 KILX 061748
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1248 PM CDT Mon May 6 2024

.KEY MESSAGES...

- A line of thunderstorms will push through central Illinois late
  tonight into Tuesday morning...bringing gusty winds and
  downpours.

- Scattered severe thunderstorms may fire along an outflow
  boundary along/southeast of a Champaign to Shelbyville line
  Tuesday afternoon/evening.

- Confidence is growing concerning a more significant and
  widespread severe weather event across much of central and
  southeast Illinois Wednesday afternoon/evening.

&&

.UPDATE...
Issued at 1023 AM CDT Mon May 6 2024

A weak low evident on satellite imagery is centered just southeast
of the southern tip of IL, heading slowly ENE. Bands of showers
wrapping around this system continue from around Jacksonville to
Bloomington southeastward, and should slowly diminish from the
west over the day. A few thunderstorms will be possible as well,
mainly south of a Taylorville to Danville line early this
afternoon with a few hundred J/kg CAPE forecast in that area.
Cloud cover will be fairly prevalent in the area, with more breaks
expected to the northwest of the showers. Temperatures look on
track to reach the 70s across the area, with the higher end of 70s
possible northwest of the Illinois River where more sunshine
should be available. Updates have been made to extend
precipitation chances farther northwest late this morning and
afternoon given radar trends, but otherwise the early morning
forecast package was in good shape.

37

&&

.SHORT TERM...(Today through Tuesday)
Issued at 313 AM CDT Mon May 6 2024

A short-wave trough evident on 07z/2am water vapor imagery over
southern Missouri will continue lifting northeastward into the
Ohio River Valley today. Showers associated with this feature will
spread as far northwest as a Bloomington to Jacksonville line:
however, precip amounts will be quite light. Instability will
remain limited across much of central Illinois, but SBCAPEs
increasing to 500-1500J/kg warrants thunder mention along and
southeast of a Danville to Taylorville line. Showers will exit
into Indiana before sunset as short-wave ridging leads to a period
of dry weather this evening into the first half of the overnight.

Meanwhile further west, an organized line of convection will
develop ahead of a much stronger short-wave crossing the Rockies
into the Plains late this afternoon. These storms will push
eastward and spill into the Illinois River Valley after 09z/4am.
While instability will be waning, think gusty winds and heavy
downpours will be a good bet as the line pushes through the
western KILX CWA and arrives along the I-55 corridor by dawn. All
CAMs suggest the convection will continue eastward and exit into
Indiana before midday Tuesday.

After that, attention will focus on the exact placement of the
residual outflow boundary...which will play a key role in late day
thunderstorm development. At this time, it appears the boundary
will likely lay out along/near I-70. With a highly unstable/sheared
environment to the south across the Ohio River Valley, any cells
that form will be capable of damaging wind gusts and large hail.
The primary time frame will be from 3pm to 9pm before the storms
shift further east out of the area.

Barnes

.LONG TERM...(Wednesday through Sunday)
Issued at 313 AM CDT Mon May 6 2024

After another lull in precip chances Tuesday night into Wednesday
morning, all eyes will be on a potential outbreak of severe
weather Wednesday afternoon/evening from the Ohio River Valley
southwestward into the southern Plains. Low pressure is progged to
track eastward out of the Plains into central Illinois...with GEFS
mean sea-level pressure suggesting the low will slide along the
I-72 corridor during the evening. A highly unstable/sheared
environment will once again be in place south of the low
track...with GEFS probabilities of exceeding SBCAPEs of 500J/kg
and bulk shear of 40kt of 30-40% along I-72 and greater than 80%
along/south of I-70. NAM 0-3km VGP values increase to 0.5-0.7,
strongly suggesting supercell development along the warm front as
well as within the warm sector. As a result, all severe weather
hazards will be in play...including damaging wind gusts greater
than 60mph, very large hail, and the potential for long-track
tornadoes. At this time, the greatest risk for widespread severe
weather will be along/south of I-72: however, this area will be
fine-tuned as exact details become more defined over the next
24-36 hours.

Once the low tracks into Indiana Wednesday night, the severe
potential will come to an end and a much cooler/more stable
airmass will arrive by the end of the week. High temperatures will
be in the 60s while overnight lows drop into the 40s Thursday
through Sunday. In addition, periodic shower chances will occur as
the Great Lakes/Midwest remains in a northwesterly flow pattern
aloft.

Barnes

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1248 PM CDT Mon May 6 2024

Scattered light rain showers continue along and SE of the I-72
terminals this afternoon, and these showers should slowly diminish
toward evening. Although most cigs/vsbys are VFR, an area of
MVFR/IFR cigs was noted at KSPI and southward. Guidance shows cigs
should lift gradually and the area shifts eastward. Probabilities
for MVFR cigs look too low for mention at KDEC, but this will need
to be watched the next few hours. Otherwise, the main feature for
TAFs is a line of thunderstorms expected to arrive at the central
IL terminals around 09Z, sweeping through the area by around 15Z.
Guidance suggests a period of MVFR cigs/vsbys as this line moves
through, as well as strong gusty winds, especially KBMI-KSPI
westward, and have included a tempo for these features with
estimated timing. Additional scattered thunderstorms likely to
begin developing around 17Z. Otherwise, winds E-SE around 10 kts,
shifting to SW during the forecast period, and increasing to
around 15 kts with gusts 20-25 kts by 17Z.

37

&&

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

$$