IWX issues Area Forecast Discussion (AFD) at Sep 2, 1:07 PM EDT
473
FXUS63 KIWX 021707
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
107 PM EDT Wed Sep 2 2026
.KEY MESSAGES...
- Heat and humidity continue with peak heat indices around 100
degrees today.
- 10% chance of a stray thunderstorm this afternoon. 20-40%
chance of thunderstorms beginning early Thursday morning.
Storms may produce damaging winds. Low confidence at this
time.
- Not quite as hot Friday and Saturday, but shower and storm
chances persist (30-50% chance).
&&
.DISCUSSION...
Issued at 242 AM EDT Wed Sep 2 2026
The well-advertised upper-level ridge remains the primary story this
morning, bringing heat and humidity and a non-zero chance of a stray
thunderstorm. Water vapor imagery shows the ridge axis cresting
northern Illinois and even far southern Michigan. Upstream
convection over northern IA and southeast MN has been rather cyclic
in its intensity on IR Satellite, but the eastern extend of activity
is expanding across central-southern Lake Michigan. Given the ridge
axis placement, high confidence in dry conditions this morning.
However, while I've shipped out a dry forecast today (10% PoP), I
cannot completely rule out a stray thunderstorms this afternoon. The
primary forcing mechanism could be a departing 500-mb jet streak,
but this focuses primary across central MI and into Ontario.
Meanwhile, a second group of CAMs suggests renewed, isoalted activity
along the IL-IN border in the 4p-6p ET window. This might be forced
by a lingering outflow/MCV from the aformentioned upstream activity.
Will pass this on to the incoming shift for further consideration.
Otherwise, very hot and humid once again today with highs in the low-
90s, dew points well into the 70s resulting in heat indicies of 100-
105 (as seen yesterday).
On Thursday, the 500mb ridge folds somewhat in response to a
disturbance wrapping up over interior Ontario. The result locally is
an increasing chance for showers and thunderstorms as the day
progresses. Timing is uncertain, with some guidance favoring the
overnight period instead of the late-afternoon. Our hot and humid
environment will be supportive of isolated severe thunderstorms,
but this risk is highly conditional on how any upstream activity
evolves. These storms also decrease forecast confidence in the
temperature forecast for Thursday. Due to anticipated cloud debris,
we'll hold off on any extension of the heat advisory.
With the upper-level ridge somewhat displaced, we could remain
within an active period into at least the start of the Labor Day
weekend with showers and storms around both Friday and Saturday.
Beyond this, there is some indication the ridge may wash back north
early next week. High temperatures Monday and Tuesday have a
comically large spread (10+ degrees Tuesday) among the guidance,
with the in-house blend on the cool-side. With that much spread,
precipitation chances are likewise unclear. Given the trough working
its way across the Cascades and through Montana, I would favor the
ridge axis to revisit Indiana early in the week. No signs of fall
quite yet.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 105 PM EDT Wed Sep 2 2026
A larger scale upper level trough continues to migrate eastward
this afternoon across eastern Ontario/western Quebec. Another
smaller scale short wave across eastern North Dakota will also
take an eastward track well north of the local area. With the
bulk of large scale forcing remaining north of the local area,
questions still remain as to extent of any convection as far
south as northern Indiana through this period. Another shot of
advective forcing is expected to overspread the southern Great
Lakes later tonight which could cause some elevated convection
to develop in vicinity of a slowly southward propagating
boundary across Lower Michigan. Given the late timing and more
elevated nature to instability by this time, confidence remains
too low for shower/storm inclusion with the 12Z TAFs. May also
need to watch remnant outflow boundary across north central
Indiana to southern Lake Huron vicinity for possible isolated
convection this afternoon due to moderate/strong instability.
Current thinking is isolated convection along this boundary
would have greatest chances to the east and north of the
terminals. Otherwise, VFR conditions expected this period with
low level gradient favoring continued south-southwest winds.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
INZ005>009-103-104-203-204.
Heat Advisory until 8 PM EDT /7 PM CDT/ Thursday for
INZ012>015-017-018-020-022>027-032>034-116-216.
OH...Heat Advisory until 8 PM EDT this evening for OHZ001-002-004-
005.
Heat Advisory until 8 PM EDT Thursday for OHZ015-016-024-025.
MI...Heat Advisory until 8 PM EDT this evening for MIZ078>081-177-
277.
MARINE...None.
&&
$$
DISCUSSION...Brown
AVIATION...Marsili
Source: IWX issues Area Forecast Discussion (AFD) at Sep 2, 1:07 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202609021707-KIWX-FXUS63-AFDIWX)
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