692
FXUS63 KIWX 172235
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
635 PM EDT Tue Jun 17 2025

.KEY MESSAGES...

- Humid with shower and storm chances (20-50%) later tonight
  into Wednesday morning, mainly over nw IN and sw MI.

- Enhanced risk for severe thunderstorm Wednesday afternoon
  into Wednesday evening (2-11 pm EDT). All hazards possible.

- Very hot and humid conditions this weekend into early next
  week.

&&

.DISCUSSION...
Issued at 227 PM EDT Tue Jun 17 2025

Lingering low-mid level shear axis and moisture gradient over our
far southeast (Marion IN to Lima OH area) may allow for a few
showers/storms to persist this afternoon. Most of the area will
largely remain between forcing mechanisms into this evening
otherwise with mainly dry and humid conditions.

A low amplitude, convectively aided wave upstream is expected to
lift east-northeast toward the lower Great Lakes later tonight into
Wednesday morning. The low level jet responds and supplies a
low level theta-e surge into mainly our nw IN and sw MI zones
where clusters of primarily elevated convection will be
possible. The excellent moisture advection with 1.75" plus pwats
may support locally heavy rainfall and flooding if convection
develops.

Attention into Wednesday afternoon and evening turns to a round or
two of convection, potentially severe. Synoptically, a more
pronounced mid level shortwave (convectively enhanced) will track
east toward the lower Great Lakes inducing a deepening sfc
reflection through near the WI/IL border into lower Michigan. Low to
mid level southwest flow deepens in advance with expectations for 35-
45 kts of 0-6 km bulk shear. Near 70F sfc dewpoints and expectations
for highs to reach into the 80s will lead to at least a moderately
unstable boundary layer by this time with ~2000 j/kg or more of
MLCAPE possible. As always, mesoscale uncertainties remain, such as
remnant outflow boundary position from Wed AM activity and cloud
debris. CAMS are also somewhat split on timing with a potential pre-
frontal trough and MCV into western zones as early as 17-18z, or the
primary wave/cold front being the main event later in the afternoon
and early evening. Regardless, all hazards, particularly wind damage,
are on the table in this environment with any any organized line
segments and/or supercells.

Post-frontal air mass will provide brief relief from the humidity on
Thursday with a few lingering showers not out of the question early
in the day east of Interstate 69. Heat wave then continues to appear
locked in by this weekend into early next week as an upper level
ridge expands over the region.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 627 PM EDT Tue Jun 17 2025

Shaping up to be a period of active weather within this TAF
period. An area of convection is underway over west-central IL
drifting northeast. This is  on the leading edge of an upper-
level low will lift toward the Great Lakes. Forecast guidance
suggests that this activity is favored to survive to KSBN after
06z. Instability will be waning by that time but a strengthening
low-level jet to the southwest along with nonzero elevated
instability may be enough to maintain the ongoing convection.
Preceding this, cumulus continues to develop along a lake breeze
currently just north of KSBN. Cumulus has struggled thus far
but not enough confidence to remove the TS chance these next
couple hours, thus, it remains. Confidence is low for the near-
term TS.

At KFWA, opted to maintain the inherited TS near 13z Wednesday,
though confidence is low that the IL activity survives that far
east. Instead, KFWA is better positioned for a round of severe
storms Wednesday afternoon. Confidence in timing is medium at
best with some discrepancy in guidance; will need to see how
mesoscale boundaries lay out in the morning.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Air Quality Alert until midnight EDT /11 PM CDT/ tonight for
     INZ005-012>015-022-023-103-104-116-203-204-216.
OH...None.
MI...Air Quality Alert until midnight EDT tonight for MIZ078-177-
     277.
MARINE...None.

&&

$$

DISCUSSION...Steinwedel
AVIATION...Brown