-- Discussion containing changed information from previous version are highlighted. --
516
FXUS63 KLOT 131526
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1026 AM CDT Sun Jul 13 2025

.KEY MESSAGES...

- Increased chance of showers and perhaps some thunderstorms
  today across central IL into northwest Indiana south of the
  Kankakee River.

- Shower and thunderstorms chances will increase each day
  Tuesday through Thursday.

&&

.UPDATE...
-- Changed Discussion --
Issued at 1026 AM CDT Sun Jul 13 2025

Overall forecast for today remains on track, though slight
changes were made to shower and storm chances in north-central
IL for this afternoon.

A shortwave trough and it`s associated baggy surface low
continue to traverse across eastern OK and western MO this
morning. As a result, a broad area of showers and embedded
thunderstorms has been developing in central MO and is expected
to move into central IL and eventually central IN later today.
While the current trajectory of the wave and surface low should
keep the greatest coverage of showers and thunderstorms south of
US-24, forecast soundings do show 600-800 J/kg of MLCAPE
developing into the far southern portions of our CWA which
should be sufficient to support some scattered showers and
isolated thunderstorms. Accordingly, have decided to increase
POPs a bit into the 40-50% range mainly for areas along and
south of a Pontiac, IL to Rensselaer, IN line where the better
moisture and instability are forecast to overlap. Main timeframe
for any scattered showers and storms in this area will be
between 12 PM and 7 PM CDT today.

Elsewhere, rain-free conditions can be expected as drier mid-
level air remains overhead. However, the combination of cirrus
blow off from aforementioned storms and wildfire smoke will
keep a partly to mostly cloudy look to the skies through this
evening. Despite the clouds, temperatures will still get into
the mid-80s this afternoon.

Yack
-- End Changed Discussion --

&&

.DISCUSSION...
Issued at 318 AM CDT Sun Jul 13 2025

Diffuse and weakening cold front extends from lower Michigan
southwest to Missouri. Little or no sfc convergence or pressure
trough evident anymore, just some lower dewpoints north of where
the front used to be. Forcing for showers and storms today will
be provided by mid-upper level southern stream trough over the
central/southern Plains. This shortwave is progged to shear out
today with the northern portion of this trough pushing east
across Missouri into central Illinois this afternoon.

There has been a significant upward trend in model guidance with
respect to coverage of precipitation toward across our southern
CWA. POPs for today have been adjusted upward again, but are
still lower than what most model guidance would support. Given
the absence of any low level forcing and some tendency for
guidance to already be too aggressive with QPF across northern
Missouri, have opted to keep the increase in POPs today somewhat
measured. If observational trends this morning catch up with the
more aggressive model guidance, then forecast for today will
need to be updated to raise POPs and perhaps inch temps down a
bit more.

Farther north, much lower dewpoints are filtering into the area
and should make for a much more comfortable feel to the air
mass today. A considerable amount of high level cloudiness
should spread across northern Illinois from that southern stream
trough, which when combined with smoke aloft from Canadian
wildfires, should be pretty effective in filtering sunshine
today. HRRR guidance does show increasing concentrations of
wildfire smoke down to the surface today, but given the same
model`s forecast of nearly unrestricted visibility, have opted
to not include smoke in the weather grids for today. However,
certainly possible that the smell of smoke will be present in
the air today.

The southwestern portion of that shearing out southern trough
is progged to get trapped beneath developing low amplitude
northern stream ridging across the Midwest Monday into Tuesday.
There will probably continue to be primarily afternoon and early
evening "air mass" thunderstorms in the vicinity of this subtle
upper level trough. Monday afternoon, the bulk of the air mass
convection could end up south of our CWA assuming the drier more
stable air mass does indeed spread south into central IL, as it
is generally progged to do by most guidance.

By Tuesday, the higher theta-e air mass should begin to spread
back north into the area as low level southerly flow becomes
established. The area favored for greater chances/coverage of PM
convection looks to be our southern CWA Tuesday. Some
differences arise between the ECMWF and GFS with how quickly
northern stream trough and associated cold front drop
southeastward into and eventually across the area. While not a
washout, it does look like the chance for at least scattered
convection will increase Wednesday into Wednesday night. The
threat will probably linger into Thursday, unless the timing of
the trough ends closer to the faster GFS solution.

Warm and humid conditions are expected again by Tuesday and
should last until the front clears the area sometimes Wednesday
night or more likely Thursday. More comfortable humidity,
seasonably warm temps, and probably a couple day break in the
rain is expected Friday into Saturday.

- Izzi

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 552 AM CDT Sun Jul 13 2025

Smoke concentration from Canadian wildfires is expected to
increase today, with even the potential for some near surface
smoke. The HRRR smoke model keeps sfc VSBY unrestricted, so
didn`t introduce any VSBY restrictions in the TAFs, but will be
something to monitor today. Otherwise. VFR conditions are
expected today. Light westerly winds are expected, though there
will be a weak lake breeze that will flip winds to northeast at
GYY this afternoon. The lake breeze is expected to remain east
of ORD and MDW.

- Izzi

&&

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

&&

$$

Visit us at weather.gov/chicago