945
FXUS63 KILX 070112
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
812 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.

&&

.UPDATE...
Issued at 810 PM CDT Mon May 6 2024

Line of severe storms is moving across NE/KS this evening and
approaching KS/IA this hour. Latest CAMs suggest this line will
reach the lower Illinois River Valley by around 09/10Z or 400/500 AM
CDT isolated storms popping up ahead of the main line around
08Z/0300 CDT. Given the unfavorable diurnal timing, storms should be
in a weakening trend, but couldn`t rule out some strong/severe
storms reaching as far east as central Illinois. Latest RAP suggests
pockets of 1000 J/kg MLCAPE will still be in place as the line
arrives with deep layer shear of around 30kt which would support
a continuing severe threat.

Deubelbeiss

&&

.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 00z TAFs through 00z Tuesday Evening)
Issued at 646 PM CDT Mon May 6 2024

A line of thunderstorms currently stretching from Nebraska to
Oklahoma will continue to move east overnight, crossing the
central Illinois terminals late tonight. Storms should be in a
decaying phase, but may still be strong producing gusty winds. A
period of MVFR ceilings and briefly IFR ceilings will accompany
the precip tonight. A warm front will lift north across the region
Tuesday morning with SE winds ahead turning SSW behind. A few
spotty showers and storms are possible during the day Tuesday, but
low coverage precludes any mention in the forecast at this time.

Deubelbeiss

&&

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

$$