042
FXUS63 KIWX 181846
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
246 PM EDT Mon Aug 18 2025

.KEY MESSAGES...

- Chances of showers and storms (30-55%) return for tonight into
  Tuesday. Severe weather is not expected at this time, but a
  few storms could produce some locally heavy rainfall and gusty
  winds to 40 mph.

- Remaining hot and humid Tuesday with heat indices in the
  upper 80s to middle 90s.

- Confidence increasing in cooler and drier conditions mid-late
  week into early next week.

&&

.DISCUSSION...
Issued at 242 PM EDT Mon Aug 18 2025

Showers and thunderstorms that originated along the IN-IL line this
morning have refused to diminish and continue to slide slowly
east. This is despite a dry, easterly surface wind, weak flow
aloft, modest instability and poor shear. Storms developed on a
remnant outflow boundary from overnight storms and have been
aided by an warm front nosing into Illinois. This activity is
becoming outflow dominant which makes additional eastward
progress questionable. Subtle low-level capping is in place as
well.

In far northern Illinois, thunderstorms have begun to develop on the
interface of not only the warm front, but the outflow boundary of a
Wisconsin MCS. This activity has flat-lined a bit and has otherwise
been poorly modeled today. Should an organized line develop over
Illinois this afternoon, it will encounter a stable air mass from
the ongoing storms over far northwest IN. Instead, the area to watch
this afternoon and evening is over eastern IA, squarely in the warm
sector of this low moving through the upper Midwest. Satellite in
eastern Iowa is beginning to bubble up with cumulus which could be
the origin of tonight`s storms. The best upper-level forcing will be
north of our area and instability and shear continue to be limited
locally. This minimizes the overall severe weather risk locally, yet
the strongest of storms could produce damaging wind gusts. Heavy
rain rates are expected as well, with 1" per hour rates possible.

Decaying showers/storms linger into Tuesday morning followed by
possible reinvigoration along and east of I-69 Tuesday
afternoon as long as instability can blossom as advertised.
Shear will remain poor, limiting the overall severe risk, but
the cold front will provide ample forcing.

In the wake of the cold front, not has humid, with dew points in the
60s Wednesday. A stretch of dry weather is anticipated
Wednesday through at least the start of the weekend. There is
only a slight chance of showers Saturday afternoon as a
moisture- starved cold front moves through. This cold front will
bring a refresh dose of Canadian air resulting in Sunday high
temperatures in the 70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 130 PM EDT Mon Aug 18 2025

A weak wave continues to move into northwestern IN bringing
showers/thunderstorms over KSBN for the next couple of hours
along a baggy warm frontal boundary that is north to south
orientated over the western parts of the forecast area. Did
have vsbys drop down into IFR cat to around 1 to 2SM with the
heavier rainfall from these thunderstorms. Expectation is this
activity does keep moving slowly eastward through the remainder
of the area this afternoon/evening however the activity should
wane as it does and current thinking is that it diminishes
before it gets to KFWA.

A second batch of showers and thunderstorms currently over
northern IL will move into the area later tonight and should
approach KSBN after 06z Tue and KFWA after around 10z Tue but
will most likely be in a decaying state. Therefore, a bit of
uncertainty as to the coverage and intensity with the loss of
diurnal heating but did opt to keep Prob30 mentioning in for
both sites at this time. With the heavier showers/storms MVFR
conditions are expected, but is possible for a temporary drop of
vsbys into IFR category but confidence is very low in that
outcome.

&&

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

&&

$$

DISCUSSION...Brown
AVIATION...Andersen