396
FXUS63 KLOT 130818
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
318 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.

&&

.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 /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1227 AM CDT Sun Jul 13 2025

Can`t rule out some MVFR VSBY this morning in HZ/FU, but for the
most part, VFR conditions are expected through the TAF cycle
with light westerly winds. There will be a weak lake breeze that
will flip winds to northeast at GYY this afternoon. Current
expectation is that the lake breeze will remain east of ORD and
MDW, but could be close for MDW especially.

- Izzi

&&

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

&&

$$

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