616
FXUS63 KIND 161930
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
330 PM EDT Wed Sep 16 2026

.KEY MESSAGES...

- Hot temperatures will continue at times into Saturday,
  especially south. Heat indices in the low 100s again today and
  Thursday.

- Narrow bands of 2 to 4 inches of rain will be possible tonight
  through Thursday morning within persistent rounds of
  thunderstorms over NE central Indiana. A Flood Watch has been
  issued from 12 AM to 2PM EDT.

- Shower and storm chances persist for much of the time into
  next week, with temperatures turning cooler next week

&&

.DISCUSSION (This evening through Wednesday)...
Issued at 329 PM EDT Wed Sep 16 2026

Today...

Much of weather over the last 36 hours has been dominated
by a large, broad area of high pressure over the SE CONUS. A
combination of a strong subgeostrophic upper jet and weak low
pressure over the Atlantic has subdued the amplitude and strength of
ridge, with the upper jet now dipping into portions of the Ohio
Valley.

In the lower levels, a closed low and associated SW jet is exiting
to the NE. This jet pushed large amounts of moisture into the
region, of which has created a broad area of instability over
central Indiana. Latest soundings indicate SBCAPE values of around
1500 J/kg, with 2500 J/kg expected by late this afternoon. With
convective temperatures around 90 degrees, a broad cirrus shield,
and a modest low level warm layer, convection is likely going to be
confined to weakly forced areas along residual outflow boundaries.

The severe threat today will be rather limited with bulk shear
values less than 20kt, but lapse rates in the mid to upper levels
are steep enough for a few isolated strong cores to develop. In
these cases, a brief area of enhanced winds (likely 40-50MPH) would
be possible.


Tonight...

As we head into the overnight period, a weak positively tilted
trough will approach from the NW. As this interacts with the high
pressure to the south, confluence will promote the development of a
nocturnal LLJ. This in combination with a modest low level boundary
and a saturated thermal profile will likely lead to a narrow (50-
100mi) corridor of persistent thunderstorms. Model guidance is still
widely varied on placement of these thunderstorms, with the latest
HREF LPMM highlighting a corridor of 3-5" over E/NE Indiana.
Confidence is not high on if NE central will be within this narrow
corridor, but the margin of error is low enough, and the impact
potential is high enough that a Flood Watch has been issued for far
N/NE central Indiana from midnight tonight until 2PM EDT tomorrow
encompassing the greatest timing concern of 4AM to 11AM EDT.

Severe weather a distant secondary concern overnight, but the mid
level lapse rates due remain steep enough for a few stronger cores
to be embedded within the persistent thunderstorm threat. For this
reason, isolated gusts of 40-50 MPH will be possible overnight.

The LLJ will weaken with diurnal heating on Thursday, of which
should dampen convective initiation late Thursday morning into the
early afternoon. This should lead to a lull in thunderstorms for a
portion of tomorrow before diurnal convection returns along remnant
boundaries in the late afternoon and evening.

Friday and beyond...

The upper high will continue to gradually retreat southwest. The
surface front will sink far enough south initially to keep PoPs low
on Friday, but it will return north again on Saturday as an upper
wave interacts with the front. This will bring more rain chances,
mainly north.

After a brief reprieve from heat for many areas Friday, hot
conditions return on Saturday as the front moves back north.

Sunday into next week, larger upper waves moving through will keep
chances for rain around. Cooler air will filter back into the area,
with highs by Tuesday in the upper 70s to middle 80s.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 121 PM EDT Wed Sep 16 2026

Impacts:

- Thunderstorms are possible at KIND/KHUF and KBMG this afternoon
  and evening.

- Thunderstorms are expected at KLAF late tonight and possibly again
  at KIND/KHUF Thu morning.

- MVFR ceilings expected to occur at KLAF towards 12Z Thu.

Discussion:

Convection is anticipated to develop over portions of central IN
generally near and south of I-70 over the next few hours along
residual outflow boundaries. Convective temps from morning
soundings suggested temp near 90 F was sufficient for development
and recent ACARS soundings from KIND suggest little inhibition
remaining. Recent radar trends are showing the first signs of
echoes to the west of KBMG. Have added PROB30s for -TSRA with MVFR
vis for BMG/IND/HUF this afternoon into the evening to account
for the expected scattered convection.

Overnight, the primary frontal boundary will have shifted northward
towards KLAF and northern portions of central IN. With an
approaching weak shortwave, thunderstorm activity is expected to be
more numerous around KLAF after 06Z as the low level jet increases
into the boundary enhancing convergence. There is some chance that
this greater coverage of TS will move towards KIND/KHUF by 12Z
Thursday and have introduced PROB30 for TSRA for this scenario
through 18Z.

There is decent agreement that ceilings will fall overnight with low
level cooling and saturation associated with both convective outflow
and rainfall further N-NW of central IN. Ceilings are expected to
fall into the MVFR range for KLAF towards 12Z with IFR ceilings
possible with convection.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch from midnight EDT tonight through Thursday afternoon
for INZ031-038-040>042-049.

&&

$$

AVIATION...Crosbie
DISCUSSION...Updike/50