271
FXUS63 KILX 261731
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1231 PM CDT Thu Jun 26 2025

.KEY MESSAGES...

- Hot and humid weather will persist into the upcoming weekend.
  The highest heat index readings of 100 to 105 degrees will occur
  today...but will remain in the upper 90s to around 100 degrees
  through Sunday.

- Rain chances will be minimal today (20% areal coverage), but
  will increase markedly by Friday into Saturday.

&&

.DISCUSSION...
Issued at 324 AM CDT Thu Jun 26 2025

...Heat Advisory...

Typical summertime heat and humidity will persist today. High
temperatures will top out in the lower to middle 90s and dewpoints
will hover in the lower to middle 70s...resulting in peak afternoon
heat index values of 100 to 105 degrees across the board. Have
therefore added Knox, Stark, and Marshall counties back into the
Heat Advisory that is in effect through early this evening. An
approaching cold front will bring increased cloud cover and rain
chances for Friday: however, heat index values will still climb to
around 100 degrees or perhaps a few degrees higher along/east of
I-57. Future shifts may need to extend the Heat Advisory into
Friday for the eastern KILX CWA if current trends continue. After
that, very warm and muggy conditions will persist through the
weekend...with heat index values topping out in the upper 90s to
around 100 degrees for both Saturday and Sunday.


...Daily Thunderstorm Chances...

Isolated convection will develop in the hot/humid airmass this
afternoon: however, with no significant focusing mechanism
present, areal coverage will remain minimal (around 20%).

As low pressure tracks from Iowa this evening to Lake Huron by
Friday evening, it will give the persistent frontal boundary that
has been stalled to the N/NW of the region a push southward. A
broken line of thunderstorms will develop along the slowly
advancing front across eastern Iowa and northwestern Illinois
late this afternoon and evening. These storms will gradually shift
E/SE, but will be in a weakening state as they push into the
Illinois River Valley toward midnight. Model solutions vary
concerning how far the convection will make it into the KILX
CWA....with some solutions such as the HRRR and WRF-ARW suggesting
it will barely get to the Illinois River. Meanwhile other more
bullish models like the FV3 show storms perhaps getting as far
east as the I-55 corridor overnight. Given the moderately to
strongly unstable pre-frontal environment, have trended more
toward the FV3 with this forecast package. As a result, have
spread 30-50 PoPs into the Illinois River Valley and 20 PoPs as
far east as I-55 overnight.

While the boundary will be weakening with time, it will still
provide enough focus within the moisture-rich environment to
warrant 50-60 PoPs along/east of the I-55 corridor by Friday
afternoon. As the front slowly makes its way southeastward, the
50-60 PoPs will focus along/southeast of I-55 on Saturday.

Once the Friday/Saturday front drops into the Ohio River Valley
and washes out, the synoptic focus for convective development will
be lost on Sunday. Current forecast features 40-50 PoPs mainly
across the west, but think these are overdone and will likely
need to be reduced with subsequent forecast packages.

As has been advertised for the past few days, a vigorous short-wave
trough traversing the zonal flow pattern across southern Canada
will dig into the Great Lakes/New England early next week...displacing
the upper ridge over the SE CONUS westward into the Rockies.
Given deepening northwesterly flow aloft, a significant cold front
will makes its way through the region on Monday. An increased
chance for thunderstorms will accompany the front...followed by a
return to cooler/drier weather by next Tuesday and Wednesday.

Barnes

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1235 PM CDT Thu Jun 26 2025

Isolated convection to occur again this afternoon and early
evening across central IL in very unstable tropical air mass.
Carried VCSH/VCTS to address this chance through sunset and SPI
recently had VCTS. Models have trended weaker and slower with a
line of convection tracking southeast toward the IL river/PIA from
08-12Z and carried VCSH for this chance as well. More convection
to develop during midday Friday though best coverage to be after
18Z/1 pm Friday. SW winds around 10 kts this afternoon to veer SSW
5-10 kts after sunset and SW winds increase to 10-15 kts with
gusts near 20 kts after 15Z/10 am Friday.

07

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT this evening for ILZ027>031-036>038-
040>057-061>063-066>068-071>073.

&&

$$