203
FXUS63 KIWX 121035
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
635 AM EDT Sat Jul 12 2025

.KEY MESSAGES...

- A few showers and storms possible early this morning across NW
  Indiana and SW Lower Michigan.

- Scattered thunderstorms are expected to redevelop today, with
  the greatest coverage expected in the 3pm to 9pm EDT
  timeframe.

- The most favored locations for isolated strong to severe
  storms are east of Interstate 69 and possibly extending into
  northwest/west central Indiana south of US Route 24. The
  primary threats are isolated damaging wind gusts and locally
  heavy rainfall.

- Hot and humid today with peak afternoon heat indices of 95 to
  100, especially east of Interstate 69. Uncertainty in
  thunderstorm timing/coverage leads to some lower confidence
  with hourly temperatures/heat index trends this afternoon.

- Brief shot of dry and less humid weather Monday, but heat is
  expected to return by Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 328 AM EDT Sat Jul 12 2025

Many of the forecast thoughts regarding convective/heat potential
remain intact this morning. Much of the local area remains in Slight
Risk for severe storms in SPC Day 1 Outlook, with primary concerns
on isolated damaging wind gusts and a potential of some localized
flooding.

MCS across western Great Lakes was not able to make much eastward
progress last evening through the early overnight hours this morning
before decaying. The downstream mid/upper level ridge has been quite
stubborn and was likely aided in its strength by its proximity to
upstream convection across the western Great Lakes. A few showers
and storms have attempted to develop over the past hour along a
residual outflow boundary across northwest Indiana and would suspect
that this potential will continue eastward into SW Lower MI/NW
Indiana early this morning. MCV likely associated with decaying N IL
convection should lift northeast and shear out this morning which
could help to take this weak sfc trough/outflow boundary eastward
across northern Indiana through early afternoon. Cannot rule out
some isolated convection as this occurs given ongoing strong low
level moisture transport across the region.

The primary concern remains this afternoon/evening for stronger
storms. The aforementioned sheared vort max/remnant outflow
associated with decaying northern IL convection could be a
focal point for isolated-scattered storms into early this
afternoon. Another feature to watch is a mid/upper level trough
across northern Missouri, which appears to have some interior
PV anomaly enhanced from strong convection over the past 12 to
18 hours. The eastward progression of this feature across
northwest IN/northwest OH into early evening may be the primary
area of greater convective coverage this afternoon.

HREF mean still keeps primary instability axis across NE IN/NW
Ohio where eastward progressing axis of pooled low level
moisture in pre-frontal area and warmer low level temps will
maximize instability (2-3000 J/kg). Deep layer shear profiles
are quite weak, and generally westward displaced (in closer
proximity to the incoming MO short wave) from better instability
across eastern portions of the forecast area by later this
afternoon. The concern remains for isolated-scattered strong
wind gusts in this setup with some potential of a few wet
microbursts given high low level theta-e air and steep 0-2km
lapse rates maximizing along and east of the I-69 corridor this
afternoon. RAP DCAPE progs do suggest an axis of 1200-1500 J/kg
values shifting east of I-69 this afternoon which could support
a few precip loaded stronger downdrafts. Greatest severe
potential should reside in the 18Z-00Z timeframe, but given
marginal shear setup, expecting a primarily multicell setup to
limit severe coverage. One item that may need to be watched
today is possibility that some isolated severe potential could
evolve far southwest portions of the CWA depending on
evolution/timing of the MO wave, and if sufficient
destabilization can occur ahead of this feature.

While shear profiles will be weak, uniform southwesterly flow
of around 20 knots should provide some storm movement to
mitigate higher end flood concerns, but high PWATS and some
training in this unidirectional flow environment is possible
that could lead to isolated flooding.

The other item of concern for today is the increased heat/humidity.
Primary pre-frontal thermal ridge should advect into far NE
IN/NW Ohio this afternoon. Convective initiation may be a bit
more delayed across NW Ohio which should allow at least some
mid-upper 90s heat indices. Given mid-late afternoon increase in
convective chances, did not have the confidence to hoist any
heat headlines at this time.

Multicell clusters will likely diminish across the east this evening
with some potential of isolated-scattered showers and storms
developing along the primary cool front across the northwest.
Migration of best low level moisture into eastern portions of
forecast area by this time and northeast ejection of better
upper support from Upper Midwest forcing should limit coverage
however.

Not much change to the forecast for Sunday with less humid
conditions for the bulk of the area and enough suppression of
frontal boundary by this time to keep bulk of shower/storm
chances south/southeast of the local area.

The break in the hot and humid conditions early week will be short
lived as mid/upper level heights recover by Tuesday/Wednesday
downstream of an active short wave pattern from Pacific NW into the
Northern Plains. Some return warm frontal forcing could provide
chances of showers and storms again by later Tuesday/early Wednesday
followed by a possible broader synoptic cool front late work week
with additional storm chances. However, given low amplitude nature
to this pattern, confidence in temperature forecast and duration
of cool air intrusions for Thursday and beyond is a bit on the
low side given region could be positioned in fairly strong low
level baroclinic zone under this flow pattern.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 635 AM EDT Sat Jul 12 2025

Weak shortwave and associated frontal boundary will approach the
area later today and support SCT convection commensurate with
diurnal destabilization. Hi-res CAM`s still show a fair amount
of spread in timing and coverage given weak and delayed
forcing. However, confidence is increasing that KSBN will be
missed by any afternoon storms and the best chances for KFWA
will be roughly 20-00Z. Will hold with a PROB30 at KFWA though
given lingering timing uncertainty. Otherwise VFR expected to
prevail.

&&

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

&&

$$

DISCUSSION...Marsili
AVIATION...AGD