760
FXUS63 KIND 160545
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
145 AM EDT Wed Sep 16 2026

.KEY MESSAGES...

- Few showers and storms tonight, isolated heavy rain greatest
  threat

- Additional showers and storms tomorrow along with temperatures in
  the upper 80s to low 90s

- Shower and storm risks persist through late week along a slow-
  moving frontal boundary

&&

.FORECAST UPDATE...
Issued at 1001 PM EDT Tue Sep 15 2026

Slowly approaching, eastward-sliding boundary will combine with
surprisingly large fetch of anomalously high precipitable water
values in excess of 2.00 inches to promote continuation of widely
scattered, sub-severe RW/TRW across northern counties this evening.
Despite damp column, decreasing confidence in rain/thunder chances
through the overnight hours with better forcing staying just north
of the CWA, and if anything slight negative mid-level differential
vorticity advection.  Storm motion has been/is expected to be high
enough to thwart any flash flood concerns.  Anomalous dewpoints for
mid-September will only allow overnight minimums around 70F across
the northern tier, and low 70s elsewhere.

&&

.DISCUSSION (This evening through Tuesday)...
Issued at 211 PM EDT Tue Sep 15 2026

Overview.

After a stormy night tonight, hot and humid conditions will peak on
Wednesday before a slow-moving front brings additional showers and
thunderstorms to Central Indiana. Outside of a strong wind gust in
the strongest storms of the day, the main threat will be localized
heavy rainfall and flash flooding. Rain chances will linger into
Thursday as the front becomes quasi-stationary over the area.
Another stronger cold front will push through late this weekend into
early next week bringing additional rain and cooler temperatures.

Tonight Through Thursday.

Rain coverage is expected to gradually ramp up during the evening
and early overnight hours as a front approaches from the west and
interacts with a hot and humid airmass over the state. The CAPE
profile will be skinny, but deep peaking in the mid-adternoon hours
at around 1500 J/kg. During the overnight hours, convection is
expected to be elevated and driven more by frontal lift. Overall,
the severe threat looks minimal with the weak instability profile
and elevated nature of the storms, but with 30-40kts of shear as the
LLJ ramps up, can`t rule out a storm overperforming. The main threat
looks to be localized heavy rain with the HREF max showing pockets
of 2-2.5 inches in spots. Overall, most areas will see generally a
half inch or less, but those localized areas could see minor
flooding.

Another hot and humid day is expected for Wednesday with a much
more saturated vertical profile in the aftermath of the storms
Tuesday night. Surface dew points will be in the low to mid 70s with
highs topping out in the upper 80s to low 90s. Convective debris may
limit the higher-end temperature threat, but will have to monitor.
With peak heat index values generally in the upper 90s to low 100s,
not expecting a need for a Heat Advisory at this time, especially
considering the potential for cooler spots due to convection and
clouds.

As a quasi-stationary baroclinic zone sags into northern and central
portions of the state Wednesday afternoon, shortwave energy embedded
in zonal flow aloft will interact with a highly unstable airmass.
Sounding profiles from the HRRR show SBCAPE values expanding to 1500-
2000 J/kg by mid-afternoon but shear looks fairly minimal at 15-
25kts. Additional showers and storms look likely throughout the day
as the front remains in the area.Warm cloud depths exceeding 4000
meters and boundary-parallel mean flow vectors favor high
precipitation efficiency and potential training cells, which may
allow for additional localized heavy rain and flash flooding.

The surface front will slowly push southward across Southern Indiana
on Thursday and become somewhat less pronounced as the main upper
shortwave exits into the Great Lakes. While the loss of strongest
PVA and a weakening LLJ will reduce overall convective intensity,
lingering mid-level moisture and surface convergence along the
boundary will maintain high shower and thunderstorm coverage through
Thursday afternoon before post-frontal drying initiates Thursday
night.

Friday Through Tuesday.

Generally hot and humid conditions are expected again Friday into
the early weekend with the jet stream further north towards the
Great Lakes and broad ridging across much of the Gulf states. There
is some uncertainty as to any lingering impacts of the front from
earlier in the week with some potential for a fairly sharp
temperature gradient across the forecast area with the cooler air to
the north and the warmer Gulf air to the south. Overall confidence
is low with many details uncertain as to where the front will settle
out.

A broader synoptic pattern shift takes hold towards the late weekend
as operational GFS and ECMWF guidance, supported by GEFS and EPS
ensemble means, drive a deepening mid-level trough across the Upper
Midwest and Northeast. This front will bring additional showers and
storms Sunday into Monday along with cooler weather to start the
work week.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 145 AM EDT Wed Sep 16 2026

Impacts:

- Convection will be around this morning, mainly at KLAF

- Additional isolated to scattered convection possible this
  afternoon

- Variable winds, especially early in the period

Discussion:

Initial convection should be out of KLAF by valid time, and most
convection should remain northwest of KLAF for much of the predawn
hours. More convection will move into the KLAF area around 12Z but
should exit by afternoon.

Otherwise, confidence in convection is low. Numerous outflow
boundaries may trigger an isolated shower early this morning at the
other sites. This afternoon, isolated to scattered convection will
develop, but where they do is uncertain thanks in part to those
boundaries. The boundaries will also keep wind direction variable.

Outside of convection, odds favor VFR conditions.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...AGM
AVIATION...50
DISCUSSION...White