469
FXUS63 KIWX 011803
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
203 PM EDT Thu Oct 1 2026

.KEY MESSAGES...

- Rain and isolated thunderstorms this evening through mid-
  morning Friday. Rainfall totals on either side of 1 inch.

- Notably cooler Friday through the weekend with highs in the
  60s.

- Very crisp Tuesday morning with lows in the 30s (70% chance).


&&

.DISCUSSION...
Issued at 202 PM EDT Thu Oct 1 2026

Warm, breezy, with increasing clouds for the remainder of the day
followed by rain and isolated thunderstorms as a cold front sags
southeast. Excellent moisture return from the Gulf is evident on
water vapor, as anticyclonic flow off a southeast US ridge funnels
moisture poleward against a low swirling over the OK Panhandle.
Forecast soundings overnight depict an impressive warm-cloud layer
of 12,000 ft, indicative of a moisture-rich atmosphere. Boundary-
parallel flow through the column will limit the front`s forward
speed. As a result, fairly high confidence in rainfall amounts
tonight through late-morning Friday on either side of 1". Some high-
resolution ensembles have a few stripes of 2" totals which is
certainly possible from any isoalted thunderstorms that bubble up.
Yet overall, with 10-day observed rainfall of less than 0.50", the
general feeling is that the forecast area can handle this rainfall.
We can address any near-term flood concerns with Flood Advisories as
needed.

Circling back to thunder for a moment, the best time for an isoalted
thunderstorm is from about 4pm to 10pm EDT when a narrow ribbon of
instability is maximized; still shy of 1,000 j/kg. Tonight`s rain
looks to be primary rain event for the next seven days. Low pressure
through Ontario threatens to bring showers Sunday to central and
northern Michigan, while a second system takes a similar path late
next week.

Sharply cooler behind the front resulting in highs Friday through
the weekend only in the 60s with Canadian high pressure moving in.
As mentioned here this morning, Tuesday morning looks absolutely
crisp with lows in the 30s. Advertised lows could be 2 to 3 degrees
on the cold side of available guidance (shy of the 25th percentile),
but within the realm of possibility. Fear not, as temperatures appear
poised to rebound late in the week as upper-level troughing moves
east.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 120 PM EDT Thu Oct 1 2026

A cut-off upper level low across Central Plains will continue to
get ingested by a more progressive northern stream flow across
the Great Lakes region into early Friday. The combination of the
eastward progression of this feature and a weaker northern
stream upper level short wave trough kicking out of the Corn
Belt will allow for a southeast sagging low level frontal zone
to push across northern Indiana tonight into early Friday.
Evolution of these features will allow for strengthening axis of
925-850 mb fgen forcing late this afternoon from central IL into
south central Lower Michigan. Some convective cells could
develop along a differential heating zone across far northern
Indiana, with an eventual transition to more of a solid rainband
this evening. Some weak surface based instability (200-500 J/kg)
could yield isolated thunder potential between 21Z-00Z but point
probabilities are too low at this time to include with the 18Z
TAFs. Cigs should deteriorate to IFR later tonight as the
baroclinic zone drops south with a northwest to southeast
improvement back to VFR Friday morning as drier low level air
works in behind the front.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory from 11 AM to 11 PM EDT Friday for LMZ043-
     046.

&&

$$

DISCUSSION...Brown
AVIATION...Marsili