704
FXUS63 KILX 251746
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1246 PM CDT Wed Jun 25 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 and Thursday...but will remain in the upper 90s to around
  100 degrees through Sunday.

- Rain chances will be limited over the next couple of days
  (20-30% areal coverage)...but will increase markedly by Friday
  into Saturday.

&&

.UPDATE...
Issued at 1055 AM CDT Wed Jun 25 2025

Current forecast for today and tonight look on track and just
minor updates done. The main weather story is the high heat and
humidity this week and continued the heat advisory through 7 pm
Thursday (except Knox, Stark and Marshall counties) for peak heat
indices of 100-107F (highs in low to mid 90s and dewpoints in low
to mid 70s). Late morning temps already in upper 80s to around 90F
from Lincoln south with heat indices around 100F. This is a
longer duration heat wave for central and southeast that started
with the heat advisory Sat afternoon June 21st. Latest radar
mosaic shows an isolated shower in southern Livingston county
moving east toward Chatsworth and another small shower in southern
Bureau county north of western Marshall county. This cell was
along an old outflow boundary over along the Bureau and Putnam
county border sw through central parts of Stark and Knox counties.
Last few runs of HRRR model show isolated convection developing
this afternoon and early evening east of the IL river in unstable
air mass and ending after 02Z/9 pm. SPC day1 outlook has marginal
risk of severe storms north of a Rushville to Decatur to Terre
Haute line for damaging wind gusts from mid afternoon into early
evening, with locally heavy rain possible. Similar wx pattern
continues on Thursday so isolated convection possible again Thu
afternoon/evening with highest pops 30-40% nw of the IL river Thu
night.

07

&&

.DISCUSSION...
Issued at 323 AM CDT Wed Jun 25 2025

...Heat Advisory Through Thursday...

Typical summertime heat and humidity will persist this week. 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. In addition, muggy
overnight lows in the middle 70s will provide limited relief for
those without air conditioning. As a result, the Heat Advisory
will remain in effect through Thursday. Increased rain chances
will cool temperatures slightly by the weekend: however, heat
index readings in the upper 90s to around 100 are anticipated
through Sunday.


...Daily Thunderstorm Chances...

Widely scattered convection will develop in the hot/humid airmass
both this afternoon and Thursday afternoon: however, with no
significant focusing mechanism present, areal coverage will remain
quite low (20-30%).

As low pressure tracks from Iowa Thursday 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. As a
result, rain chances will increase on Friday. 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/west of the I-55 corridor by Friday afternoon. As the front
slowly makes its way southeastward, the 50-60 PoPs will focus
east 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 50 PoPs across the
board, but think these are way 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 Thursday Afternoon)
Issued at 1245 PM CDT Wed Jun 25 2025

Isolated to scattered showers and thunderstorms have developed in
past hour over central IL, especially from I-55 east and tracking
slowly ENE in a very unstable tropical air mass with SB CAPES of
3500-4500 j/kg, and PW values of 1.8-1.9 inches. Continued prob30
of TS this afternoon and early evening until 00-01Z for MVFR
conditions possible (and possibly lower vsby conditions if heavier
rains move in. Could also be gusty winds over 30 kts with any
thunderstorms this afternoon. Otherwise fairly light SSW to SW
gradient winds less than 10 kts next 24 hours over central IL
airports. Diurnally driven cumulus cloud field with scattered to
broken bases of 3-5k ft to diminish after sunset and redevelop by
late Thu morning, with isolated convection again possible Thu
afternoon.

07

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT Thursday for ILZ029-031-036>038-
040>057-061>063-066>068-071>073.

&&

$$