631
FXUS63 KILX 061958
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
258 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, as well as a few tornadoes possible.

- Scattered severe thunderstorms may re-develop Tuesday afternoon
  and evening.

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

&&

.DISCUSSION...
Issued at 258 PM CDT Mon May 6 2024

While a few showers persist in southeast/east-central IL this
afternoon associated with a shortwave moving ENE up the Ohio Valley,
this activity should gradually diminish this evening as a line of
thunderstorms organizes in the central Plains late this afternoon
and evening and sweep eastward toward central IL. Latest high-res
models are fairly unanimous with this line arriving in far west-
central IL around 2 AM a few hours past peak intensity. MUCAPE
values are forecast to be as high as 2000 J/kg as this line moves
into western MO/IA, down to 1000-1500 entering IL, and 750-1250 as
it exits IL to the east around 9 AM. This instability is also
increasingly likely to be elevated in nature as a stable layer
develops near the surface. Nevertheless, there will be a chance
for scattered severe wind gusts, especially west of the Illinois
River where SPC has denoted a Slight Risk of severe thunderstorms,
likely weakening to more isolated wind gusts as it weakens toward
the I-57 corridor. A few tornadoes could also spin up along the
line, again more likely toward western IL. There will likely be a
lull in precipitation behind this line during the morning hours,
but instability should return fairly quickly during the daytime
hours, as mean surface-based CAPE forecasts increase to 1000-3000
J/Kg (highest southeast of I-70, lower northwest of IL River).
Outflow boundaries left behind from the early morning thunderstorm
line could provide the convergence needed to start storms during
the afternoon. Strong deep-layer shear of 50+ kt should support
another round of severe thunderstorm development, containing large
hail, locally damaging wind gusts, and a few potential tornadoes.
SPC continues a Slight Risk of severe storms from around
Shelbyville to Champaign eastward, and a Marginal Risk for the
remainder of central IL counties. Predominant high-res model
guidance depicts these storms shifting southeastward out of the
area by mid evening.

The closed upper low over the Northern Plains will linger into
Wednesday, with another embedded shortwave likely inducing another
convective system Wednesday. Current model continues to track this
feature into central IL, perhaps a bit earlier with arrival in
central IL Wednesday afternoon. 1500+ J/kg and 50+ kts deep layer
shear continue to be forecast with this feature. SPC has depicted
an Enhanced Risk for severe thunderstorm from near I-72
southward, and a Slight Risk for much of the remaining area to the
north.

Following Wednesday`s system, a wavy northwesterly flow aloft sets
up for late week into the weekend, with the large scale trough axis
shifting east of IL. Although occasional precipitation chances can
be expected, amounts would be lighter, instability would be weaker
for a decrease in thunderstorm activity.

Temperatures will remain warm through Wednesday, with highs around
80 Tuesday, and Wednesday, then a strong downtrend can be expected
following Wednesday`s cold front, with highs dipping back down to
the 60s north of I-70 Thursday, and mid to upper 60s expected
both Friday and Saturday. Lows into the 40s are forecast for much
of the area each night Thursday night through Saturday night.
Temperatures will begin to trend back upward Sunday into early
next week.



37

&&

.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.
&&

$$