986
FXUS63 KLOT 261949
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
249 PM CDT Thu Jun 26 2025

.KEY MESSAGES...

- Chances of showers and t-storms will continue at times tonight
  into Friday.

- After a bit of a reprieve from heat and humidity Saturday
  (especially near the lake), another hot and humid day is
  expected Sunday.

&&

.DISCUSSION...
Issued at 249 PM CDT Thu Jun 26 2025

Another day of hot and humid conditions across the area this
afternoon. Some isolated showers and thunderstorms have brought
some temporary relief to a few places this afternoon, but the
majority of the area is experiencing another day with
temperatures in the 90s and heat index readings near or just
above 100 degrees. Atmosphere is hot, humid, and uncapped, which
has allowed for some "air mass" convection to pop this
afternoon. The threat of these isolated to widely scattered
storms could linger through sunset, but unless we get some
amalgamation of cold pools to force additional storms, coverage
should remain pretty isolated through sunset.

Water vapor imagery shows a well defined shortwave over the
northern Plains moving gradually east to the upper Mississippi
Valley. More organized convection has been developing in
association with this shortwave from southern MN south into
central IA. This convection is expected to continue to shift
gradually eastward toward the MS River the rest of the
afternoon. Stronger shear associated with this shortwave is
north of our latitude, so despite the instability, anticipate
this convection should fall apart after sunset as it crosses the
MS River into northwest IL. Kept the highest pops later this
evening into the early overnight over our northwestern CWA, with
much lower chances for this activity surviving long enough to
bring any organized rain chances over our eastern CWA.

Composite outflow/weak synoptic front is expected to move across
our CWA tomorrow. Strongest forcing associated with the
shortwave trough is expected to pass well north of the area, but
with air mass expected to become moderately to strongly unstable
and uncapped in advance of this boundary tomorrow. Certainly
plausible that scattered thunderstorms could develop ahead of
this front tomorrow afternoon, particularly across NW IN and our
east central IL counties. Slightly drier and more stable
conditions in the wake of the front should result dry weather
over our northwest CWA.

Transient surface high will move across the western Great Lakes
Saturday with lower dewpoints making the still seasonably warm
temperatures more tolerable. The position of the high should
also allow for a prominent lake breeze to move well inland
during the afternoon, providing for nature provided AC for areas
closer to the lake.

That high will scoot off the east of the region Sunday with
southerly winds likely to drag the heat and humidity back north
into the area. Highs on Sunday should top out in the low-mid 90s
with heat indices again near to just over 100 degrees. Southern
flanks of another shortwave trough passing north of the area
Sunday should lead to increasing chances of showers and storms
later Sunday afternoon into Sunday evening. Stronger shear and
better threat for organized convection should remain to our
north, but the air should be very moist and moderately to
strongly unstable again Sunday afternoon, so if convection makes
it into the area, wet microbursts and torrential downpours
would be a threat.

Longwave trough is progged to dig into the Great Lakes Region
early next week with much more comfortable humidity, especially
by Tuesday and Wednesday. Temps will remain seasonably warm
away from the lake, but not as hot as many of the days we`ve
experienced recently.

- Izzi

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1240 PM CDT Thu Jun 26 2025

Key Aviation Messages for the current TAF period:

- Widely scattered showers and storms this afternoon/early
  evening

- Another period of storms tonight that may produce gusty
  northwest winds and reduced visibilities

Widely scattered showers and storms have blossomed around the
airspace prompting VCTS to be added to Chicago terminals. Thunder
near Rockford cannot be ruled out completely this afternoon,
but chances were to low currently to mention in the TAF. Dry
periods will still exist due to the widely scattered nature of
the storms, but as storms pass an individual terminal heavier
downpours and lightning will be possible. Cigs are projected to
remain above 3000 feet, but vis may drop to MVFR levels during a
downpour. Winds will gradually become more southwesterly
through the afternoon with gusts around 20 knots.

There is another chance for storms tonight that could last past
midnight. These storms could also feature a sharp gusty wind
shift to the northwest as well as reduced visibilities due to
heavier rain. Other than when storms are over terminals, winds
will diminish overnight to around 10 knots. However, they will
pick up again after daybreak and turn to the west with gusts
around 20 knots.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

Visit us at weather.gov/chicago