598
FXUS63 KIWX 201157
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
757 AM EDT Sun Jul 20 2025

.KEY MESSAGES...

- Rain showers and thunderstorms are expected today, with two
  potential rounds of stronger storms possible along and south
  of US 30. The first round from 9-2 am EDT, the second 2-8 pm
  EDT. Primary threats will be heavy rain, lightning, localized
  flooding, and gusty winds up to around 50 mph (most likely in
  the afternoon). Confidence in stronger storms occurring is
  low. Chances for showers and storms linger into Monday
  morning.

- There is a Moderate Swim Risk for the southeastern Lake Michigan
  beaches in La Porte and southern Berrien County for today.

- Hot and humid conditions remain on track for Wednesday and
  Thursday with heat indices near or above 100 degrees.

&&

.DISCUSSION...
Issued at 345 AM EDT Sun Jul 20 2025

While signals are strong in the models for at least 2 complexes
of storms over the next 24 to 36 hours along and north of a
quasi-stationary boundary, finer mesoscale details remain
problematic with regards to the track of these systems and
impacts. Our first complex is rapidly expanding across SE Iowa
into west central IL. HRRR has been fairly consistent on the
expansion of this area as it tracks east. While fairly high
confidence exists on it moving into eastern IL, the 850-300 mb
flow and location of the theta-e gradient suggest at some point
the strongest portion of the complex will begin an SE turn in
the 12-15Z window. Have made some minor timing/pop changes
through 18Z to account for a slightly more northward trend on
the likely pops while trimming the northern extent of any pops
as you head into MI. Was tempted to increase to categorical
along and south of US-24 where greatest chance for
showers/storms exists, but given noted concerns held with
likely. Main concern will heavy rain as a very soupy atmosphere
will be in place with a swath of 0.5-1" of rain is likely on the
US-24 corridor with higher amounts in some locations. Neighbors
to the south have hoisted Flood Watches given recent rainfall
and higher likihood of even heavier rain amounts. For us, the
heaviest rain the past 24 hours fell well north of the
anticipated storm track today. In addition, the complex should
remain progressive.

Confidence decreases this afternoon and into tonight as final
track of this complex will greatly determine what, if any,
additional convection chances exist. 06Z HRRR seems to paint a
very plausible scenario with little/no storms in our southern
area from mid afternoon into early Monday in the post MCS
subsidence area. Confidence was not high enough in this setup to
remove the likely pops through early Monday, so have left them
alone with the day shift in a better position to see how the
trends look.

Upper level ridging will begin to increase late Monday into mid
week, finally ending the train of convective systems, but also
ushering in a return to hot and humid conditions. No changes
made to later periods as signals remaining consistent on
Wednesday and Thursday being the warmest days (highs near or
above 90) and heat indices near or above 100 degrees (highest
Thursday). By next weekend, the heat dome will likely have
shifted east enough to end the heat impacts and also begin to
allow at lease some chances for showers and storms to return.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 610 AM EDT Sun Jul 20 2025

Predominantly MVFR through the TAF period, with IFR most likely
at KSBN (ongoing now). An area of showers and storms will move
through early this morning just south of KSBN and west of KFWA.
A cold front is currently draped from KDTW west-southwestward to
KBEH and then KMDW, with calm or light WSW-WNW flow at the
surface. Expect a shift to more NW then gradually N as the front
sinks southward this afternoon. Additional chances for showers
and storms arrive after 2 pm along the cold front, with the
best potential for storms at KFWA (though possible at KSBN per
some of the guidance). Have VCTS and Prob30 groups to handle
that potential for now. Otherwise, ceilings to linger around
1500-2500 ft for the most part until the afternoon, when they
will lift to VFR outside of any rain or thunderstorm chances.
MVFR visibilities will linger until we can get more mixing into
the late morning. Overnight expect light N-NE winds shifting
more easterly (or becoming calm/variable).

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Fisher
AVIATION...MCD