691
FXUS63 KIWX 172333
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
733 PM EDT Mon Aug 17 2026

.KEY MESSAGES...

- Dry through the day Tuesday with mostly clear skies and lower
  humidity.

- The next chance of rain and storms arrives Tuesday evening
  into Wednesday. The risks for severe weather and flooding are
  low.

- Dry weather returns again Thursday and Friday.

&&

.DISCUSSION...
Issued at 1246 PM EDT Mon Aug 17 2026

An area of low pressure is currently exiting our area, with dry
conditions and decreasing clouds expected through the rest of the
day. Clearing is already noted upstream on visible satellite
imagery, with decreasing clouds expected throughout this afternoon
and evening. Winds from the north will keep temperatures seasonable
today with highs in the upper 70s as high pressure builds over the
Midwest and Great Lakes regions. Overnight, light winds and clear
skies will allow for lows to drop into the upper 50s and for patchy
dense fog to develop by daybreak Tuesday.

Most of Tuesday will be dry with seasonable temperatures, sunshine,
and lower humidity. Chances for rain and storms start to increase
Tuesday evening for NW Indiana and far SW Lower Michigan as a cold
front advances from the northwest. Models are increasingly
lackluster on rain and storms as the front is disjointed with
better moisture, instability, and forcing. Rain and storms will
be widely scattered Tuesday evening into early Wednesday given
weak moisture return ahead of the front and a displaced
vorticity maximum to our north as an upper level low pushes
through Ontario. Forecast soundings also show low level dry air
at 850mb Tuesday night that will need to be overcome in order
for rain to make it to the surface. Have maintained up to 60%
near Lake Michigan Tuesday evening and 30-50% PoPs elsewhere
Wednesday although it is possible the middle section of our
forecast area (between the Toll Road and US 30) stays mainly
dry given the poor dynamics; areas nearby Lake Michigan are most
likely to se scattered rain and storms Tuesday evening/night
and our far southeast counties are mostly on Wednesday given a
more favorable diurnal timing. At this time, risk of widespread
flooding is very low as is the potential for severe weather.

High pressure then builds into the Great Lakes and Midwest regions
again by the end of the week. Thursday and Friday look to be dry and
seasonable, before another system potentially arrives for the
weekend. For now, have maintained low chance PoPs (20-30%) given
high spread in model guidance.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 733 PM EDT Mon Aug 17 2026

Dry conditions are expected through most of this period as a
short wave mid level ridge builds across the area tonight.
Northwest wind gusts to 10 to 15 knots will diminish sharply
this evening as a low level ridge builds east across portions of
northern Indiana into the Ohio Valley. Mostly clear skies
tonight and light winds with the anticyclone should allow for
good radiational cooling conditions. Crossover temps should be
reached easily, although ongoing dry air advection raises some
question as to the extent of fog development overnight. This
appears to be a good setup for at least patchy shallow fog
across the area with some uncertainty as to occurrence at
terminals. Given this uncertainty will maintain previous
forecast idea of TEMPO MVFR conditions late tonight into early
Tuesday morning. The anticyclone will be progressive through the
area on Tuesday allowing for a return of southwest winds around
10 knots. Some moisture return should build back into the area
in wake of this sfc high by early Tuesday evening, more likely
across far northern Indiana/southern Lower Michigan. Will
maintain a dry forecast through 00Z Wednesday with expectation
of better rain/storm chances after this valid period as next
short wave trough approaches. Instability magnitudes could be a
limiting factor for realizing appreciable thunder potential.

&&

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

&&

$$

DISCUSSION...Johnson
AVIATION...Marsili