Severe Thunderstorm Warning 86, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
244 PM EDT Tue Jun 24 2025

.KEY MESSAGES...

- An Extreme Heat Warning remains in effect through 8 PM ET. Peak
  heat indices of 100 to 105 degrees are expected today.

- Heat indices Wednesday through Friday will be 90 to 100, with
  the highest values expected along and south of US 30.
  Cumulative effects of long-duration heat will likely cause
  significant impacts.

- Near record warm overnight low temperatures in the low to mid
  70s through the weekend will provide little to no relief from
  the heat, especially for vulnerable populations.

- Thunderstorms will become numerous most afternoons and
  evenings through Friday. Storms may become strong to severe
  with damaging winds as the main hazard.

&&

.DISCUSSION...
Issued at 243 PM EDT Tue Jun 24 2025

An area of surface high pressure and an expansive upper level
ridge will continue bring high heat and oppressive humidity to
the area this week. The Excessive Heat Warning remains in effect
through 8 PM ET today. Ample WAA and moisture transport from
the Gulf will yield highs in the low to mid 90s and dewpoints in
the mid 70s over the this afternoon. Slightly 'cooler' through
the weekend with highs in the upper 80s to near 90 degrees. Near
record overnight lows in the mid 70s will offer little to no
relief from the heat, so cumulative impacts from the heat and
humidity are likely. Peak heat indices later today between 100
to 105 degrees area-wide. The NWS Heat Risk shows major to
extreme (levels 3 and 4 out of 4) heat impacts will be possible
for the rest of today. Stay hydrated, take breaks if you must be
outside, and check in on those who could be especially
vulnerable to the high heat and humidity. Additional heat
headlines may be needed beyond Tuesday with heat indices peaking
between 95 to 100 degrees, especially along and south of US 30.

As the upper level ridge flattens out by midweek and chances for
rain/storms return, we may get some temporary reprieve from the
dangerous heat. The temperature forecast will be highly dependent on
if we get any storms or remnant outflow boundaries over the area.
Daily diurnal chances for scattered rain/storms exist this week from
today through Friday. A cold front has stalled over southern
Wisconsin/northern Illinois (a bit further west than previously
anticipated) and an outflow boundary moved through our area earlier
this morning. In the wake of this outflow boundary, pop-up
afternoon/evening pop-up scattered showers and storms are possible
later this afternoon and evening as the atmosphere destabilizes.
Storm initiation has already occurred over NW Indiana and SW Lower
Michigan with numerous sub-severe storms ongoing. Given that the
airmass over the area is very moist, there are steep low-level lapse
rates, and it will be very unstable (~2500 to 3000 surface based
CAPE this afternoon), it is plausible that some of the storms today
could be strong to severe. The Storm Prediction Center currently has
us in a Marginal Risk (level 1 of 5) for severe weather (and again
on Wednesday and Thursday). The primary hazards would be damaging
wind and heavy rain should any severe storms develop. Additional
chances for scattered strong to severe storms will be possible
Wednesday and Thursday as the aforementioned front slowly sags
southward towards and through our forecast area over the next 24-48
hours. With our area on the northern periphery of the ridge, storms
will likely ride the fringes of the ridge or develop along any
remnant outflow boundaries. With a pattern like this, it is tough to
know exactly where/when/if storms will develop because each day is
dependent on mesoscale features (such as outflow boundaries) and
models don't always have the best handle on storm coverage.

The upper level ridge pattern flattens out this week and looks to
potentially break down over the weekend. By early next week, it is
possible we get a reprieve from the heat and temperatures drop back
to near normal levels.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 117 PM EDT Tue Jun 24 2025

The outflow boundary located SW to NE across northern IN this
morning is now serving as a point of thunderstorm initiation this
afternoon, which may impact KSBN. There appears to be a small
concensus of models that suggest TSRA stays north of KFWA thanks
to our dominant ridge, but will maintain the PROB30 for the
time being. Still low confidence on whether or not additional
storms overnight arriving from Illinois impact KSBN. This second
round would be highly dependent on the afternoon's storm
coverage. Showers and thunderstorms will also be possible again
by late morning Wednesday.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Extreme Heat Warning until 8 PM EDT /7 PM CDT/ this evening
     for INZ005>009-012>015-017-018-020-022>027-032>034-103-
     104-116-203-204-216.
OH...Extreme Heat Warning until 8 PM EDT this evening for OHZ001-
     002-004-005-015-016-024-025.
MI...Extreme Heat Warning until 8 PM EDT this evening for
     MIZ078>081-177-277.
MARINE...None.

&&

DISCUSSION...Johnson
AVIATION...Cobb

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Special Weather Statement
National Weather Service Northern Indiana
316 PM EDT Tue Jun 24 2025

MIZ079-080-241945-
St. Joseph MI-Branch MI-
316 PM EDT Tue Jun 24 2025

...STRONG THUNDERSTORMS WILL IMPACT NORTHEASTERN ST. JOSEPH AND
NORTHWESTERN BRANCH COUNTIES THROUGH 345 PM EDT...

At 316 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Homer to near Centreville. Movement was
east at 20 mph.

HAZARD...Wind gusts up to 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Three Rivers, Union City, Centreville, Colon, Nottawa, Girard,
Leonidas, Mendon, Sherwood, Fairfax, Wasepi, Findley, and Hodunk.

This includes Interstate 69 in Michigan between mile markers 20 and
21.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4184 8544 4195 8563 4207 8526 4207 8489
TIME...MOT...LOC 1916Z 262DEG 19KT 4218 8488 4194 8549

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

JA

Special Weather Statement
National Weather Service Northern Indiana
344 PM EDT Tue Jun 24 2025

MIZ080-081-242015-
Branch MI-Hillsdale MI-
344 PM EDT Tue Jun 24 2025

...STRONG THUNDERSTORMS WILL IMPACT NORTHEASTERN BRANCH AND
NORTHWESTERN HILLSDALE COUNTIES THROUGH 415 PM EDT...

At 344 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from 6 miles southeast of Burlington to near Quincy.
Movement was east at 15 mph.

HAZARD...Wind gusts up to 50 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Coldwater, Hillsdale, Jonesville, Quincy, Union City, Litchfield,
Long Lake, Girard, Allen, Lake Wilson, South Butler, Marble Lake, and
Hodunk.

This includes Interstate 69 in Michigan between mile markers 11 and
21.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Northern Indiana.

&&

LAT...LON 4187 8464 4187 8496 4207 8514 4207 8469
TIME...MOT...LOC 1944Z 262DEG 14KT 4205 8499 4189 8489

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH

CLH