970
FXUS63 KIWX 151809
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
209 PM EDT Tue Sep 15 2026

.KEY MESSAGES...

- Warm and humid conditions to persist into Thursday with
  chances for showers and thunderstorms (40 to 70%) through the
  period. Challenges continue determining the most favorable
  periods, location and impacts across the area.

- If storms can organize or interact into this evening, a few
  could produce strong to locally severe wind gusts with the
  greatest chance between 6 pm and midnight ET.

- Repeated rounds of showers and storms could lead to some areas
  experiencing hydrologic concerns.

&&

.DISCUSSION...
Issued at 208 PM EDT Tue Sep 15 2026

The potential exists for multiple rounds of showers and
thunderstorms into Thursday as a slow moving and eventually quasi
stationary boundary sets up across the area. This leads to an
overall low confidence forecast and a more initially conservative
approach, especially in later periods.

In the near term, scattered showers and storms have continued to
develop and move NE across far NW areas with some indications on
satellite development may calm down in this area as the frontal
boundary shifts northeast. Low level moisture is increasing with an
axis of 500 to 1000 J/KG of MUCAPE into SW areas ahead of a remnant
boundary/trough residing from central Lower MI to near Chicago and
then to Quincy IL. This will most likely be the focus for additional
showers and storms as we move through the remainder of the
afternoon into this evening with locations closer to Lake MI
seeing activity first. The best shear will remain disconnected
from this boundary and best upper dynamics will push NE leaving
little for storms to work with in terms of organization. Combine
that with decreasing, but not zero, instability after sunset
leads to low confidence on how long any convection survives as
well as risk for renewed development. While I suspect even
likely pops may be overdone into this evening, will leave them
in place during the most favorable window when a weak waves does
move in. Although the marginal risk for severe continues (wind
threat), this may very well be more of a potential hydro issue
with time. Initially, much of the area can take some rainfall,
but if any training occurs this could quickly change as PWATs
over near 2" which could result on 1 to maybe 2 inch per hour
rates.

Beyond tonight, consensus of surrounding offices was generally to
back away from any pops higher than chc given the lack of
consistency in the models, difficulty in timing specific waves and
location of the boundary. Combination of soupy airmass (dewpoints
upper 60s to low 70s), generally uncapped atmosphere (assuming no
convective inhibition from other storm complexes) and pockets of
heating will lead to mainly diurnally driven development outside of
any MCVs or waves. One item to note is the SW to NW flow currently
in place will transition to more west east as the upper flow
flattens out. The chances for localized flooding may then increase
somewhat given the weak flow and risk for training. WPC keeps much
of the area in a Marginal Risk for Excessive rainfall, with Wed
depicting Slgt chc into parts of the area along the forecasted
location of the front.

Forecast left untouched beyond Thursday as the frontal boundary will
likely osculate across the area with 500 mb heights of 594 to 597
dm across the area which may be enough to push the boundary somewhat
further north. However, as we get to the weekend another trough will
slowly edge east and reach the western Dakotas Sunday with a series
of weak disturbances helping to displace the ridge south and
hopefully bring a break in the humidity. Highest pops currently
reside Sat/Sat night and may be overdone (likely to some
categorical) but that far out no changes warranted.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 150 PM EDT Tue Sep 15 2026

Focus for this aviation weather period will be potential of
showers and thunderstorms, particularly this evening and then
again overnight. A residual outflow boundary from overnight
convection is sprawled from west central IL to Chicago vicinity
and into southwest Lower Michigan. This boundary has been the
focus for a few isolated showers and thunderstorms this
afternoon, but this focus should remain NW of KSBN over the next
few hours. Approach of primary cold front later this evening and
increased moisture pooling ahead of the front should promote
scattered shower/storm development after 22 or 23Z across NW
Indiana with axis shifting southeast late evening/overnight.
Best MLCAPE profiles are expected to reside across NW Indiana
this evening with gradually waning instability overnight.
Greatest confidence in some scattered thunder is at KSBN this
evening, with lesser confidence at KFWA as instability
magnitudes wane by the time stronger forcing arrives. Frontally
forced showers/embedded thunderstorms should increase overnight
into Wednesday AM but confidence in extent of thunder remains
quite low at this time given limited instability. MVFR
conditions are expected to develop late tonight into Wed AM in
wake of frontal passage with some cigs below 2k feet appearing
likely for a time Wed AM.

&&

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

&&

$$

DISCUSSION...Fisher
AVIATION...Marsili