Severe Thunderstorm Warning 233, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
106 PM EDT Sun Aug 9 2026

.KEY MESSAGES...

- There remains the potential for severe thunderstorms late this
  afternoon and tonight. Damaging winds, flash flooding and an
  isolated tornado possible.

- Additional severe thunderstorms and flooding possible Monday
  afternoon into Monday night.

- Seasonable temperatures are expected to persist.

&&

.DISCUSSION...
Issued at 1243 PM EDT Sun Aug 9 2026

Focus remains on convective evolution and intensity late this
afternoon into tonight. Surface warm front is on schedule in
reaching to near the MI border during this time, allowing for a
muggy and unstable air mass to settle in for most locations under
perturbed west-northwest flow aloft.

There still appears to be two windows for convection, though
there might not be much of a break between them. The first
window is late this afternoon into early this evening as a small
scale bowing segment and MCV (currently near Milwaukee)
continues east-southeast interacting with the warm front and
substantial MUCAPE axis. New, scattered, sfc based cell growth
appears likely along its outflow in the vicinity of the MI state
line 20-01z. Marginal deep layer shear profiles expected here
initially, along with forcing and colder temps aloft bypassing
north may allow weak capping to limit coverage and intensity
somewhat. That said, ~2000 j/kg of MLCAPE and the current
forward momentum of the cluster could support a damaging wind
and non-zero tornado threat into mainly southwest MI and far
northern IN during this time.

The second window comes later this evening into the overnight hours
as the warm front becomes invigorated by an incoming small scale
impulse and deeper moisture advection on the nose of a ~40 kt
low level jet. There still may be a damaging wind threat with
any bowing segments given the lingering MUCAPE and increasing
deep layer shear, with an isolated tornado still not out of the
question. The bigger concern by this time with be the flash
flood potential given the potential for training/backbuilding
and a deep warm cloud layer wherever the composite outflow
stalls. This placement will depend on how the late afternoon-
early evening activity evolves (strength of cold pool/outflow
uncertain). This will need to be closely monitored regardless
given the hybrid Maddox/frontal flash flood look to this.

This periodically stormy pattern will likely continue into at least
Monday and Tuesday as several small scale perturbations track east-
southeast in the vicinity of the lingering frontal zone and
associated MUCAPE axis. Forecast specifics are very uncertain in
this kind of pattern (take it one day at a time) given the subtle
nature to the forcing mechanisms and the influence of previous
convective episodes on where exactly the frontal boundary sets up
for the next round. As for Monday, expect a lull Monday morning
before chances for severe storms increase during the afternoon hours
as strong diurnal boundary layer destabilization develops under 30-
40 kts of 0-6 km shear. Damaging winds appear to the primary threat,
with another round of training storms and flash potential Monday
night as the low level jet ramps back up.

Trends in guidance continue to favor a trend toward drier/less
active conditions mid to late week as previous episodes of
convection hopefully force the effective boundary off to the
south.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1248 PM EDT Sun Aug 9 2026

A convectively enhanced short wave across southeast Wisconsin
will continue eastward into Lower Michigan through this
afternoon. Low level flow will gradually increase to the south
of MCV-like feature across Wisconsin with additional cells
expected to develop along an outflow boundary dropping across
northern Illinois. Some uncertainty remains with how convection
will continue to develop but would expect given ample downstream
destabilization that convective development is likely into NW
Indiana in the 20Z-23Z timeframe. No major changes anticipated
to the TSRA mention at KSBN. Thunder potential at KFWA may be a
bit more delayed until later this evening without outflow
boundary expected to stall across northern Indiana and
interacting with LLJ for additional storms. The potential exists
for these storms to grow upscale into southward/southeastward
propagating MCS overnight, but timing/location are still of
somewhat lower confidence. A stronger instability gradient will
likely be positioned across northern Indiana on Monday setting
the stage for additional storms/thunderstorm complexes during
afternoon and evening hours.

&&

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

&&

DISCUSSION...Steinwedel
AVIATION...Marsili

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