Notre Dame, Indiana Weather Forecast Discussion

502
FXUS63 KIWX 200524
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
124 AM EDT Sat Sep 20 2025
.KEY MESSAGES...
- Another warm day on Saturday with highs into the 80s.
- Low chances (20-40%) for showers and isolated storms enter the
  forecast into mainly western IN and southwest MI on Saturday.
- Daily chances (40-60%) for showers/storms Sunday through Tuesday.
&&
.DISCUSSION...
Issued at 214 PM EDT Fri Sep 19 2025
A persistent blocking pattern that has provided the area with upper
ridging and associated warm/dry wx gradually breaks down into this
weekend as broad troughing over the northern Plains finally releases
east into the MS River Valley and western Great Lakes. The upstream
leading warm front and moisture axis makes slow inroads into western
IN and sw MI later tonight into Saturday morning, nearing the I-69
corridor by Saturday afternoon-evening. The largely elevated nature
to the moisture advection and northwest bypass of more pronounced
vorticity advection warrants holding on to lower end PoPs (20-40%)
for scattered showers along this weak warm front. Guidance does
hint at some weak diurnal instability developing on Saturday
for a non-zero iso thunder risk west of I-69, although our
recent dry spell hints at a greater mixout of mid-late day sfc
dewpoints than modeled. Another warm day otherwise on Saturday
with at least a partly to mostly cloudy sky.
Chances for much needed rain/iso storm chances do increase Sunday
through Monday night. Deeper moisture advecting in, and numerous
vorticity maxima tracking through in broad cyclonic flow, will
provide these periodic shower/storm chances. There will be dry
stretches in between these smaller scale (convectively augmented)
mid level impulses, with ensemble guidance pointing to Sunday and
Monday aftn-night for higher measurable rain chances (50-60%).
Slight cooler highs, yet increasingly humid, the story otherwise
during these periods.
Forecast confidence quickly diminishes Tuesday through Friday as
renewed riding over southern Canada eventually cuts off an expansive
low/trough somewhere across the Mid MS and OH Valleys. Models always
struggle with these cut off, meandering, lows at this range. Opted
not to veer from daily NBM rain chances (20-50%) as a result with
the trough and frontal zone in the vicinity. Temperatures hover
pretty close to seasonal norms otherwise for the mid-late week
periods.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 117 AM EDT Sat Sep 20 2025
A lead short wave across east central Illinois will lift
northeast across northern Indiana through the overnight hours.
Shower activity should remain west of the terminals overnight as
better moisture profiles remain displaced to the west. For later
today, a larger scale synoptic trough will acquire some more
negative tilt across the Corn Belt with a broad low level
confluent zone setting up from the southern Great Lakes to the
Ohio River Valley. This evolution should allow some eastward
migration of primary instability axis into northwest
Indiana/southwest Lower Michigan this afternoon. Did include a
TEMPO SHRA mention at KSBN this afternoon coincident with better
vorticity advection with this trough. Confidence wanes with
eastward extent at KFWA for shower potential given a bit less
instability across northeast Indiana. Isolated thunder is
possible this afternoon, particularly at KSBN, but confidence
in coverage remains too low for inclusion with the 06Z TAFs at
this forecast distance.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Steinwedel
AVIATION...Marsili

NWS IWX Office Area Forecast Discussion