IWX issues Area Forecast Discussion (AFD) at Sep 21, 2:36 PM EDT824
FXUS63 KIWX 211836
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
236 PM EDT Mon Sep 21 2026
.KEY MESSAGES...
- A mainly dry weather pattern ahead. Some pockets of light rain
or drizzle are possible rest of today into Tuesday, with just
a low chance (20-40%) of light rain showers east of
Interstate 69 continuing Tuesday night into Wednesday.
- Below normal temperatures through the end of the work week
followed by some moderation in temperatures.
- Dangerous swimming conditions are expected on southern Lake
Michigan beaches through early this evening.
&&
.DISCUSSION...
Issued at 235 PM EDT Mon Sep 21 2026
The transition to a much quieter weather pattern will continue
this week. Any additional rain chances through the middle of
the week will have no impact on current river stage/flooding
situation across the area. Dry weather is expected to continue
for the Thursday through Sunday period.
Upper level flow pattern today is characterized by a cut-off
negative upper height anomaly ejecting out of the
Nebraska/South Dakota vicinity with a low amplitude downstream
character of flow across the southern Great Lakes and Ohio
Valley. Smaller scale perturbations continue to work through
this low amplitude flow locally with the more distinct of these
short waves tracking across far northeast Indiana/northwest Ohio
this afternoon. Some slightly dry mid level air is advecting
into the region this afternoon which may continue to provide
some pockets of light rain/drizzle in association with the
departing short wave into early this evening. Additional
rainfall amounts generally expected to be one tenth of an inch
or less, although cannot completely discount possibility of an
isolated higher amount (south of US 24 across NW Ohio) given
relatively stalled position of 850 mb front and some lingering
respectable PWATS of 1.25 to 1.4 inches. However, additional
rainfall today into tonight is not expected to provide any
meaningful impact to ongoing river levels and status of
minor/moderate flooding across portions of Wabash/Maumee basins.
A secondary area of light rain/drizzle today has been across extreme
NW Indiana into mainly NE Illinois where some inverted troughing has
been enhanced by lake induced low level thickness ridging across
western portions of Lake Michigan. Given nature of northeasterly
flow profiles, higher chances of rain in this forcing pattern should
stay over the open waters or across northeast Illinois. The pattern
over the next few days with persistent easterly flow and favoring of
mid level subsidence will likely keep a frontal inversion in place
resulting in a likely difficult time eroding low clouds from much of
the area.
For temperatures tonight, a weak secondary cool frontal boundary is
expected to drop across the southern Great Lakes and should
provide the coolest temperatures to southern Lower Michigan.
However, possibility that cloud cover could linger for much of
the area, fairly well mixed near sfc levels, and wind gusts
remaining above 10 mph overnight, suggest temperatures will not
bottom out too much with expectation of lows from upper 40s to
lower 50s most areas.
A persistence forecast has been maintained for Tuesday in terms of
temperatures with thermal advections gradually waning tonight into
early Tuesday. From a large scale synoptic perspective, the upper
trough across the Plains will slowly push eastward to the Mid MS
Valley with an eventual beginning of phasing with secondary negative
upper height anomaly across Ohio. Any precip should be quite
limited Tue/Tue night with lingering dry mid level air a
deterrent. Could see scenario again where thermally induced
thickness ridge over Lake Michigan helps focus a few showers
across northwest Indiana, and perhaps along/east of I-69 where
some lingering low level moisture could reside. Have maintained
some slight chance PoPs these periods.
Looking toward the middle of the week, continued phasing of the two
negative upper height anomalies should eventually allow low-mid
level theta-e ridge to wrap back northwestward to the southern Great
Lakes. This could be enough to yield pockets of light rain showers
mainly along/east of I-69 Wed but confidence is quite low.
An overall quiet weather regime still looks to maintain its hold
Thursday to the weekend with eventual departure of this phased upper
low allowing for mid/upper level height recovery and gradual
modification of low level temperatures by Saturday and Sunday as low
level southwesterlies are finally able to develop. Precip prospects
look low through Monday as any Pacific waves trying to top the
central CONUS ridge will likely encounter less than ideal moisture
profiles locally during this period.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1231 PM EDT Mon Sep 21 2026
Overcast skies persist today and tonight due to CAA and gusty
northeasterly winds. Winds will continue to be sustained around
12 to 15 kts through this evening with gusts as high as 20 to
25 kts, especially at KFWA. Winds remain elevated overnight
before becoming gusty again late tomorrow morning. Ceilings are
expected to gradually lift overnight into tomorrow morning; IFR
ceilings prevail at KFWA before becoming MVFR by midday Tuesday.
Closer to Lake Michigan at KSBN, clouds are expected to
diminish with VFR ceilings through the TAF forecast period. Dry
conditions are expected area-wide.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Beach Hazards Statement until 4 PM CDT this afternoon for
INZ103.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for LMZ046.
&&
$$
DISCUSSION...Marsili
AVIATION...Johnson
Source:
IWX issues Area Forecast Discussion (AFD) at Sep 21, 2:36 PM EDT---------------
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