Severe Thunderstorm Warning 217, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
259 PM EDT Mon Jul 27 2026

.KEY MESSAGES...

- There is an Enhanced Risk for severe weather today. Clusters
  of strong to severe storms are expected this afternoon and
  evening. The greatest severe weather threat is expected from
  2pm to 10pm EDT.

- Damaging wind gusts of in excess of 70 mph are expected to be
  the main threat, with a few gusts as high as 80 mph possible.
  Isolated large hail to 1 to 2 inches in diameter is also
  possible across southwest Lower Michigan and northwest Indiana
  this afternoon. Isolated tornadoes are also possible.

- Dry and seasonable Tuesday through Thursday.

- High Swim Risk Tuesday for southeast Lake Michigan beaches.

&&

.DISCUSSION...
Issued at 255 PM EDT Mon Jul 27 2026

The main forecast concern will be on the severe weather potential
through this evening.

A complicated convective scenario is unfolding across the Great
Lakes region this afternoon. Preferred region of convective
development has been across northeast Illinois along a corridor
of low level warm/moist advection. This forcing is coincident
with strengthening upper low level flow and effective shear
profiles. Extreme instability with MLCAPES 4-5k J/kg CAPES is
situated across northeast Indiana with sharp eastward
diminishment in instability across northeast Indiana/northwest
Ohio. Cells across northeast Illinois are favoring strong cold
pools with signatures of very strong base velocity shifting
southeast across far northwest Indiana. The combination of
shallow low level southwest flow and deeper northwesterly flow
in the mid/upper levels is favor some north to south preference
in propagation vectors with the storms across northeast
Illinois. Areas west of US Route 31 across northeast Indiana
should stand greatest risk of seeing higher end thunderstorm
wind gusts (80+ mph) as the storms across NE Illinois drop
southeast. In addition to the risk of higher end damaging wind
gusts, the extreme instability will support some isolated large
hail of 1 to 2 inches in diameter. Also, the aforementioned
background shear profiles will continue to support some embedded
supercell structures with a risk of isolated tornadoes. 0-3km
shear vectors oriented from the northwest at around 30 knots
could also support a few QLCS tornado spinups where any rear
inflow jet can orient in a NW to SE fashion and where more
mature cold pools develop.

Additional storms are expected to develop across the Great Lakes
region this evening as low level front pushes southward with an
additional risk of scattered damaging wind gusts through around 02Z.
Confidence in severe gusts after 00Z does diminish somewhat however.

By Tuesday morning, the nose of the upper level jet streak will
reach the Mid Atlantic states with lagging sfc trough/cool front
expected to extend from western PA to southern Illinois. Passage of
this front will lead quieter weather conditions through the middle
of the week with temperatures/dew points closer to seasonable levels.

The next system to watch will be toward end of the work as the
potential exists for synoptic wave to become convectively enhanced
across the Dakotas. Some question exists as to instability
magnitudes as far east as southern Great Lakes/Ohio Valley with this
system with some indications of this system becoming more vertically
stacked in nature well to the west.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1245 PM EDT Mon Jul 27 2026

Cluster of thunderstorms from MKE south through ORD are the
primary item of focus for this TAF period. Rather high
confidence in storms persisting through KSBN, and perhaps a
tinge of uncertainty toward KFWA. For now, the environment is
highly supportive of sustained convection.

Behind these thunderstorms, northerly flow eventually brings an
area of stratus down behind a thermal trough descending through
Michigan prior to sunrise. As always, it is uncertain how long
stratus will persist into Tuesday.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Heat Advisory until 6 PM EDT /5 PM CDT/ this evening for
     INZ012-013-020-103-203.
     Beach Hazards Statement from late tonight through Wednesday
     morning for INZ103.
OH...None.
MI...Beach Hazards Statement from late tonight through Wednesday
     morning for MIZ177-277.
MARINE...Small Craft Advisory from 2 AM Tuesday to 2 AM EDT Wednesday
     for LMZ043-046.

&&

DISCUSSION...Marsili
AVIATION...Brown

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