IWX issues Area Forecast Discussion (AFD) at Sep 12, 2:19 AM EDT813
FXUS63 KIWX 120619
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
219 AM EDT Sat Sep 12 2026
.KEY MESSAGES...
- Scattered showers are likely (with an isolated storm or two
possible) along and south of US 24 Saturday morning through
mid afternoon. NW Indiana and far SW Lower Michigan will
remain dry.
- Warmer and humid by midweek. Low chances for rain and storms
(20%) late Sunday into Monday, with better chances (30-60%)
late Tuesday into Wednesday.
- There is a Moderate swim risk forecast on Sunday for southeast
Lake MI Beaches. Breaking waves and currents are expected.
&&
.DISCUSSION...
Issued at 110 PM EDT Fri Sep 11 2026
Surface high pressure overhead the Great Lakes region is making for
a beautiful end to the work week today with lower humidity,
seasonable temperatures, and some sunshine. High level clouds can be
seen advecting northward on visible satellite imagery but dry
conditions are expected to prevail today and tonight. Light
southeasterly winds and WAA will boost temperatures into the upper
70s to low 80s this afternoon.
A stationary front currently centered over the Ohio River Valley
will be the focus for 40-60% chances for rain and storms on
Saturday. Scattered showers are likely with potentially a
thunderstorm or two on Saturday, mainly for the southeastern half of
our forecast area. This feature will lift north as a warm front on
Saturday with an attendant 500mb shortwave. Then, an upper level
trough and surface cold front will move through the Great Lakes
region later Saturday evening. Increased WAA and moisture transport
alongside lift from the warm front will spark chances for showers
and storms, especially along and south of US 24 in Indiana and
Ohio. Scattered showers are expected to begin before daybreak
between 06- 09Z Saturday and end around 18-21Z). Severe weather
is not expected at this time, however, an isolated storm or two
will be possible due to surface based instability of up to 1000
J/kg by midday Saturday. Shear and low/mid level lapse rates
will be too weak for any organized severe weather. Northwest
Indiana and southwest Lower Michigan will likely remain dry, as
the cold front likely passes through early Saturday morning
prior to peak diurnal heating. High temperatures will be in the
low to mid 80s area-wide on Saturday.
Stay weather aware if you have plans to head to Lake Michigan on
Sunday! Behind the cold frontal passage on Saturday, waves are
expected to increase for southeastern Lake Michigan beaches in
Berrien and La Porte counties. CAA and northwesterly flow Sunday
behind the front will yield onshore flow and waves of 2-3 ft,
meaning the swim risk will be Moderate for both La Porte and Berrien
counties on Sunday. Breaking waves and currents are expected.
The rest of the weekend into early next week appears dry, with low
chances (20%) for rain/storms late Sunday into Monday morning with a
shortwave and associated upper level trough that passes through the
Great Lakes. With a potentially closed upper level low building
across the Pacific Northwest, this allows yet another upper level
ridge to amplify across the central and eastern CONUS early next
week. Surface high pressure builds over the eastern US on Tuesday
too, with return flow and moisture from the Gulf ushering in warmer
than normal temperatures and humid conditions underneath the peak of
the upper level ridge over the Great Lakes. Another frontal system
likely approaches late Tuesday and Wednesday, with additional
chances for rain and storms (30-60%). This system may be slow moving
or potentially even stall to our northwest (still mixed model
guidance results on if it actually comes through our area or not),
depending on how strong the upper level ridge is. There are no clear
signs of fall in any of the long range guidance as our forecast area
looks to remain sandwiched between hot and humid air to our south
and cooler, drier air to our north for the foreseeable future.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 157 AM EDT Sat Sep 12 2026
Predominantly VFR conditions at the terminals through the
period. MVFR conditions are possible this morning mainly at KFWA
as moisture transport/warm air advection from the south
increases ahead of an approaching upper level trough from the
west. A warm front will arrive just south of KFWA around 12z,
then lift northeast into Ontario/Lake Erie by around 18z. Have a
tempo for -SHRA/BR with MVFR vis (4SM) and ceilings (2500 ft)
between 11-15z. Much of the guidance develops light rain showers
in this period at/around KFWA, but they are pretty isolated and
are very focused towards locations further south and east. It's
possible we see BR outside of rain showers this morning at KFWA
as well given light/variable winds and increasing low level
moisture. Beyond 15z is a little more questionable, as we deal
with forcing from the mid-level shortwave and surface cold front
approaching from the west (over Lake MI by 18Z). The cold
front/shortwave move eastward into the overnight hours. In
combination with increased moisture for areas along/south of US
24, there is enough instability generated for scattered showers
and maybe even a few thunderstorms through about 23z. Confidence
re: Ceilings/visibility and whether a storm hits KFWA or not are
less clear. Added a prob 30 from 17-22z with MVFR potential to
account for this potential. KSBN looks to remain dry this
period thanks to limited moisture/dry air incoming from NW. Some
of the guidance brings in MVFR ceilings and vis (BR) early this
morning, but it appears to be limited in duration. Kept out of
the TAF for now. Winds will become more south-southwesterly
through the morning, then shift west-northwest into the evening
as they weaken.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Johnson
AVIATION...MCD
Source:
IWX issues Area Forecast Discussion (AFD) at Sep 12, 2:19 AM EDT---------------
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