408
FXUS63 KIWX 210515
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
115 AM EDT Fri Aug 21 2026

.KEY MESSAGES...

- Periodic showers and storms are expected today through
  Saturday. An isolated strong storm capable of gusty winds and
  brief heavy rain is possible west of US-31 this evening and
  east of I-69 Saturday afternoon.

- It will be breezy this weekend with gusts up to 30 mph and
  highs only in the mid/upper 70s. These gusty winds will lead
  to dangerous swimming conditions on Lake Michigan beaches.

- Dry and tranquil weather is anticipated Monday and Tuesday.

&&

.DISCUSSION...
Issued at 115 AM EDT Fri Aug 21 2026

Piecemeal arrival of seasonably deep mid/upper low this weekend will
lead to several periods of scattered showers/storms and some breezy
conditions. A few subtle vorticity shreds are expected to pass
through the area this afternoon and tonight on the leading edge of
this upper low. Forcing for vertical ascent is incredibly weak this
afternoon but modest instability is expected given surface dewpoints
still in the solid mid 60s to perhaps upper 60s. This will likely
support some widely scattered showers during the afternoon across
our central and eastern zones (very similar to yesterday) before the
more notable shortwave/convective complex enters our NW CWA this
evening. All of the necessary parameters for deep/organized
convection are marginal so not expecting much impacts but do think
it`s worth carrying a 20 PoP. (Most locations will likely remain
dry.) The evening wave features a little better mid/upper level
support in the left exit region of approaching jet streak. However,
it will likely arrive closer to sunset and thus losing the modest
(highly diurnally-driven) instability. Shear values are also on the
marginal side (around 20 kts) so while I can`t entirely rule out a
strong storm in our far western zones, the chances appear low.

Will likely have some showers continue through the overnight and
into Sat morning as the primary cold front passes. The main concern
for Sat will be in our far eastern zones during the afternoon. Here,
a favorable alignment of synoptic forcing along the cold front, some
healthy diurnal instability (driven by a moist boundary layer and
decent midlevel lapse rates), and perhaps marginally-sufficient
shear could lead to our best severe weather chances. The problem is
the surface front exits our CWA awfully early and the best midlevel
CVA trails well behind this surface front. Best severe chances may
end up just E/SE of our CWA but it will be close. Some gusty winds
expected behind this front Sat afternoon with a few gusts up to 30
mph possible given a tight gradient and efficient postfrontal
mixing. Deep, moist cyclonic flow then settles into the area Sat
night into Sun. NBM initialization came in dry but wouldn`t be
surprised to see a few isolated showers during these two periods.
Similarly breezy Sun afternoon in what will certainly feel like the
first taste of fall given dewpoints crashing to near 50F and highs
only in the mid 70s.

Anticyclonic low/midlevel flow then settles into the region for Mon
and Tue yielding what should be tranquil weather days. Will have to
keep an eye on sharp moisture gradient just to our SW but for now it
seems to remain safely far enough from our CWA borders. The next
chance of rain is associated with another decent shortwave entering
the Great Lakes late Wed and sending another cold front through the
area.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 115 AM EDT Fri Aug 21 2026

Primarily VFR conditions expected this period. Some shallow fog and
patchy stratus remain possible through the morning given light winds
and residual boundary layer moisture but confidence in impacts to
the terminals is not high. Thunderstorms will be possible during the
afternoon and evening but likely to remain very isolated given poor
mid/upper level support. Will hold off on any mention for now given
precip chances generally less than 30 percent.

&&

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

&&

$$

DISCUSSION...AGD
AVIATION...AGD