082
FXUS63 KIWX 151011
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
611 AM EDT Tue Sep 15 2026

.KEY MESSAGES...

- Hot and humid today and Wednesday. Shower and thunderstorm
  chances return this afternoon through Wednesday (40 to 70%).
  Chances may linger into Thursday as well.

- There is a marginal risk for isolated strong to severe storms
  between 6 pm EDT this evening and midnight. Main threat is
  damaging winds if storms become severe. Confidence remains low
  at this time.

- There is a moderate swim risk for Lake Michigan beaches along
  the Berrien Co, MI shoreline today. Breaking waves and
  currents expected.

&&

.DISCUSSION...
Issued at 607 AM EDT Tue Sep 15 2026

A more unsettled pattern begins today as a low pressure system (over
Ontario) brings a warm front through our area this afternoon, and
then a cold front this evening into the overnight hours. This cold
front will eventually stall out as the surface low/upper forcing
lift further into Quebec. As of this writing, better moisture
transport is just taking aim into our area. The warm front is
currently draped from WI (nearly occluded) south into central IL and
into TN/KY. Expect this to lift northeast through the afternoon. I
suspect with additional moisture moving in towards the 12-15z time
frame that we`ll see a few showers and maybe an isolated t-storm
focused up near Lake MI initially, spreading eastward with a focus
near the toll road. Most of the high res suggest these will
taper off with time or even stay limited to the Lake MI area and
near Cass/Berrien/St. Joseph Co, MI. There is still ridging
aloft and high pressure at the surface, so how much moisture
gets into this area early will determine how the showers evolve.
The NAM is the most aggressive with this line of showers/storms
extending from northern IL/Southern WI into the thumb area of
MI, having it continue southeastward through the morning and
early afternoon, gradually shifting it southward as it runs into
the ridge. Other models keep it more limited and focused
further north. For now, have pops of 20-50% for areas
along/north of US 24, increasing with northwestward extent. Have
around 55-65% for Berrien County, MI. Don`t expect any severe
weather with this earlier activity if it survives. Right now
from radar it looks as if the outflow is moving southeastward
ahead of the storms, so that will certainly keep things limited
(in addition to unfavorable timing given no
instability/capping). SPC has our CWA in a marginal risk for
strong- severe storms for the today/tonight period. This is a
highly conditional threat as it will depend on how the earlier
part of the day evolves. More showers and cloud cover in the
west/north could limit our instability. Furthermore, the timing
of the main cold front is slower than previous forecasts (around
00z its just southeast of Lake MI). We could see some storms
popping around 6-8 pm ET in the west (perhaps lingering
boundaries as well as any lake breeze could trigger things), and
if they are able to tap into decent instability we could see a
severe threat. However, the better potential really focuses
between 8 pm ET to Midnight as the cold front moves in while we
have some instability and the best forcing. The main threat
would be damaging winds (SPC has 5%), with heavy rain and
frequent lightning. ML CAPE looks to be around 1000-1500 J/kg in
the evening (best west) and around 25-40 knots of 0-6 km bulk
shear. Confidence is low (especially east of I 69), as we have
potential for earlier showers/storms/cloud debris, paltry mid
level lapse rates (5-6C/km) and the front is diminishing with
time as it runs into the ridge. Have chances for showers and
storms tonight in the 50-80% range. High temperatures will
largely be in the low-mid 80s, with potential for high 80s,
lower 90s further south and west. Heat indices look to be 95-99
degrees for these areas as humidity increases this
afternoon...but confidence for any kind of advisory was too low
given limited duration and also because if the more aggressive
NAM is correct, we could have some showers/storms/cloud cover
that limits daytime heating.

Shower and storm chances will persist through the weekend, with our
lingering stalled front becoming more E-W oriented and flow aloft
zonal to slightly troughed. This lowers overall forecast confidence
as we are susceptible to any shortwaves that ripple through the
flow, so timing is difficult to pin down. However, for Wed-Thu,
have 50-70% chances that diminish to 20-40% Friday-Fri night.
Additional potential returns as another cold front drops into
the area Sat/Sat PM into early Sun, so have pops of 30-60
percent for the most part. Highs will be in the 70s, low-mid 80s
for the majority of the period, with a couple days seeing upper
80s further south. By Sunday, highs are in the 70s.

Moderate swim risk for Lake MI beaches in Berrien Co, MI today.
Breaking waves and currents are expected. Waves of 2-3 ft will
subside to 1-2 ft later this afternoon. There will likely be
a moderate longshore current moving south to north along the
shore (as winds shift southwest), with moderate-strong
structural currents on the south sides of piers and breakwalls.
Rip currents are possible, but less likely given fairly shore
parallel flow.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 146 AM EDT Tue Sep 15 2026

Predominantly VFR to MVFR conditions at the terminals this
period, with a warm front lifting northward through the
afternoon/evening, followed by a cold front into the overnight.
There is still considerable uncertainty as to the timing of
things (mostly impacting KSBN this period). Have prob 30s for
the 12-15z period to account for any showers/storms that make it
into KSBN. Most of the models have the storms far to our west
dying out before they reach the terminal, but with increasing
WAA we could start to see some light rain showers ahead of the
line. Then we may see a quick break until the afternoon, when
guidance generates showers/isolated storms based on a potential
outflow boundary that arrives in the 18-23z time frame (dies out
before going eastward). The cold front and more likely MVFR
conditions will move through with any showers or storms along
the cold front--likely 3z-6z. Kept prob 30 in the 18-23z time,
and then have predominant showers between 1z-6z (with prob 30
for more MVFR/TSRA chances). KFWA will likely have showers and
isolated storms later in the night, towards the 3-12z time
frame. Have a prob30 at KFWA to cover MVFR conditions that are
likely within heavier showers/storms. Otherwise, LLWS this
morning at KSBN as the warm front lifts northeastward.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for LMZ043-
     046.

&&

$$

DISCUSSION...MCD
AVIATION...MCD