937
FXUS63 KIWX 171831
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
231 PM EDT Fri Oct 17 2025

.KEY MESSAGES...

- Increasing chance of showers and thunderstorms Saturday
  (30-60% chance in the morning, 60-80% chance in the afternoon).

- There is a marginal risk of severe thunderstorms which could
 produce damaging wind gusts.

- Breezy both Saturday and Sunday with wind gusts of 30 mph.
  Wind gusts to 40 mph are possible Sunday.

- Rain will be heavy at times Saturday night through Sunday
  morning.

&&

.DISCUSSION...
Issued at 228 PM EDT Fri Oct 17 2025

A classic fall mid-latitude cyclone will breeze through the Great
Lakes over the next 48 hours. This will bring beneficial rain, but
also presents the risk for gusty synoptic wind and a marginal risk
of severe thunderstorms. Damaging wind gusts will be the primary
severe storm hazard. Through Sunday evening, rain totals of 2" are
possible, but will taper off quickly to only about 0.50-1" in
northwest Ohio.

Warm air advection is underway across far southern Illinois and dew
points are already climbing into the mid-50s. This WAA is ahead of a
deep upper-level low centered over Manitoba with a surface cold
front sweeping through the OK Panhandle. A secondary low is noted
over Arkansas, which will lift north-northeast tonight and might
squeeze out a few sprinkles early Saturday morning. Instead, the
approaching cold front will be the primary driver of the day`s
severe thunderstorm risk.

Pre-frontal showers and an isolated thunderstorm may be ongoing over
far northwest Indiana and southwest Michigan by daybreak Saturday.
Instability though the morning hours will be meager; less than 200
j/kg. High resolution guidance is in strong agreement that
instability will blossom by the afternoon to the magnitude of 500+
j/kg. There is some concern still that pre-frontal debris will delay
afternoon destabilization, but as it stands now, 500 j/kg paired
with nearly 40 knots of shear yields a believable marginal severe
weather risk with damaging wind gusts as the primary hazard. Upper-
level support lags instability, with the low-level jet ramping up
significantly late in the afternoon. The best colocation of shear,
instability, and upper-level support is the US-24 corridor west of I-
69. It appears the severe weather risk should decrease from west to
east due to a loss of daytime heating. Can`t completely discount the
tornado risk but low-level hodographs are somewhat muddy and cloud
bases too elevated.

Saturday night, we are now post-frontal but cyclogenesis will be
underway as a strong upper-level jet races in from the Plains,
catching up with the departing front. This brings soaking rain
overnight and into Sunday morning. Our placement on the north side
of the surface low will permit localized rain amounts as great as 2"
by Sunday afternoon, but this limits any nocturnal severe weather
threat.

Breezy and warm Saturday ahead of this storm system with highs in
the 80s outside of Michiana, and southwesterly wind gusts of 25-30
mph. Sharply colder Sunday with highs struggling to reach 60 degrees
west of Warsaw, IN and gusty northwest wind of 30 mph to perhaps 40
mph.

The next storm system moves through the upper Great Lakes Tuesday
bringing a reinforcing shot of cold air and additional rain.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1252 PM EDT Fri Oct 17 2025

VFR conditions and southerly winds near 10 knots will persist in
advance of a cold front and approaching frontal system. A weak
lead shortwave in southwest flow may be enough to touch off a
few rain showers in the vicinity of KSBN tomorrow morning
otherwise.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Gale Watch from Sunday morning through Sunday evening for
     LMZ043-046.

&&

$$

DISCUSSION...Brown
AVIATION...Steinwedel