511
FXUS63 KILX 250355
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1055 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

- Hot and humid conditions on Tuesday will send heat indices as
  high as 105. A Heat Advisory has been introduced south of I-70.

- Thunderstorms are possible (30-50%) north of I-72 Tuesday
  morning. Another round of storms could develop Tuesday afternoon
  into evening, though confidence in where/when will be dependent
  on the morning activity.

&&

.UPDATE...
Issued at 942 PM CDT Mon Jun 24 2024

Seeing a wide range of solutions for storm evolution the rest of
tonight and Tuesday in the CAMs. The current clusters of storms
over NE IL and approaching NE IL are struggling to maintain
persistent deep updrafts. Some pulsing evident, but sub-severe
intensity has been the rule this evening.

Going forward, the consensus of the CAMs indicate a linear
complex of storms will erupt somewhere in the S MN, N IA, SW WI
area after midnight, and propagate to the south-southeast into
central IL by sunrise. Timing and location are still quite
uncertain, but SE oriented LLJ will be present as the warm front
advances into IL from the west. That should be enough to support a
late night storm system for at least our northern counties. The
line is expected to be weakening as it reaches as far south as
Lincoln and beyond, but isolated severe wind gusts and large hail
will be possible with any sustained updraft through 7 am or so.

The current forecast rain/storm chances generally follow that
scenario, so only minor adjustments were needed to PoPs/Wx to
account for the collaborated timing shifts.

Overall, no other notable adjustments will be needed to the
forecast this eve.

Shimon

&&

.DISCUSSION...
Issued at 338 PM CDT Mon Jun 24 2024

Weak frontogenesis nosing into west-central IL late this afternoon
has sparked a few isolated storms from Davenport, IA to Eureka, IL
as of 3 pm. The NamNest is the only CAM that notes this activity,
showing it ending around sunset. Added slight chance for PoPs to
account for this over the next few hours.

A surface low situated over the Northern Plains will track into the
Upper Midwest tonight. Thunderstorms are expected to develop along
the lows warm front/within the warm sector over Minnesota/Wisconsin
tonight and track southeast along an instability gradient. CAMs
show this activity approaching our northwest sometime between
10-14Z Tuesday morning. Although we will be capped, some elevated
instability may support a few stronger storms capable of strong
winds for a brief period of time before things begin to dissipate
later in the morning as the LLJ wanes.

There remains some uncertainty on how far south thunderstorm
activity will make it Tuesday morning with current thinking keeping
most of it north of I-72. Temperatures on Tuesday will likely be
greatly impacted by morning convection, with very low confidence in
high temperatures north of I-72. Ended up reducing highs by
several degrees (upper 80s) from roughly a Champaign to Macomb
line. Higher confidence for hot and humid conditions will be seen
south of I-70 where air temperatures should reach the middle 90s
with heat indices peaking around 105. A Heat Advisory has been
issued for these counties from noon to 8 pm Tuesday.

Outflow from morning thunderstorms will be the focus for additional
activity later Tuesday afternoon into evening, though there remains
uncertainty on where this will be situated. The 24.12Z HREF has
instability peaking between 2000-3000 J/kg south of I-72, though
wind shear will be on the weaker side (~20 kts). Strong to severe
storms will be possible with any convection that does develop in the
afternoon and evening, with damaging winds and large hail being the
primary hazards. Although we can use the rain, some locally heavy
rainfall could be seen with any storms on Tuesday with PWATs
approaching 2 inches.

The aforementioned low`s cold front will sag south through the area
on Wednesday, bringing the return of more seasonable temperatures
for Wednesday and Thursday. Temperatures steadily climb back into
the upper 80s to low 90s by the end of the week ahead of the next
system. A cold front will bring our next chance for precipitation
Friday night into Saturday, with temperatures briefly turning
cooler behind it.

NMA

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1054 PM CDT Mon Jun 24 2024

Confidence is low on weather impacts at the terminal sites in the
next 12 hours. Best consensus indicates a possible flare-up of
storms mid-morning on Tuesday, that dissipates after about 3
hours. Have continued a Prob30 for those MVFR conditions across
the northern TAF sites for now. Potential for that line of storms
to reach the I-72 corridor terminals is low. Southwest winds will
begin gusting to around 20 kt starting mid to late morning.
Additional storms are likely Tue evening, as a line of storms
drops south through central IL. MVFR conditions are likely, if not
IFR during heavy rain, especially for PIA/BMI.

Shimon

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon to 8 PM CDT Tuesday for ILZ066>068-
071>073.

&&

$$