968
FXUS63 KIND 190143
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
943 PM EDT Fri Sep 18 2026

.KEY MESSAGES...

- Hot temperatures will continue at times into the weekend
  especially south. Heat indices around 100 again today southwest.

- Thunderstorms possible SW of the I-74 corridor this afternoon
  and evening.

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

&&

.FORECAST UPDATE...
Issued at 943 PM EDT Fri Sep 18 2026

Fairly quiet forecast on tap through the early overnight. Later
tonight, there is still some signal of convection associated with
increasing WAA ahead of a shortwave topping the upper ridge over
eastern Corn Belt. Although the recent IND ACARS soundings show a
classic "onion" look to them with dry air in the 850-700 mb
layer, upstream soundings from ILX and ORD/MDW region show
sufficient moistening is expected to redevelop across central IN
from the W-NW. Temp trends were adjusted downward based on recent
obs. As a result some areas have seen vis fall to around 5 SM in
BR. Any fog potential will be limited by a sufficient amount of
high cloud cover initially, replaced with a renewed lower cloud
deck with the WAA.

Still a fairly strong signal in the recent HRRR runs that the
ongoing convective line/cluster over WI/IA will shift south into
northern portions of central Indiana towards midday Saturday owing
to increasing mass convergence and SE propagation into the
instability gradient expected over central IN.

&&

.DISCUSSION (This evening through Friday)...
Issued at 249 PM EDT Fri Sep 18 2026

Today through Sunday...

A synoptic boundary will continue to work its way into central
Indiana tonight into tomorrow, with a large theta-e gradient across
the state tomorrow. This gradient will generally be aligned just
north of the I-74 corridor with temperatures in the low 80s and
upper 70s to the N/E and upper 80s to the S/W.

The convection overnight created a mesoscale boundary, and has
stalled over SW portions of the state. This is being reinforced by
differential heating this afternoon, and will be the primary focus
for additional thunderstorm development over the next 6-8 hours. The
aforementioned synoptic boundary will slowly push to the SW with
time, of which will eventually will impede and push convection to
the SW as well. Until then, a broad 20-30% PoPs will be in the
forecast for areas SW of the I-74 corridor.

This all said, there is a more organized area of convection over
eastern Illinois as of 1830Z. This convection has been able to for a
cold pool, and should be able to sustain itself as it enters central
Indiana between 3-4PM. For this reason 40-60% PoPs have been added
for western central Indiana. A fairly deep stable layer in the low
levels will likely try and push this cold pool southward with time.
There still some uncertainty if this convective system will be able
to stay in balance as it continue to push through central Indiana as
the effective shear is rather limited with eastern extent. The lack
of shear and strong surface lapse rates should keep the severe wind
gust threat small, but given the strong cold pool, isolated gusts to
45MPH will be possible for a brief period this afternoon.

The remainder of the weekend will be a constant push/pull of this
lingering stationary boundary over the region creating both a minor
swing in temperatures and persistent rain chances. The best
chances for rain will be Saturday afternoon as a weak shortwave
moves SE over the stationary boundary. This wave will increase
overall shear across the area enough to support a few organized
thunderstorm clusters and a marginal risk for damaging wind gusts.

Temperatures are expected to remain warm, with some uncertainty
depending on boundary placement and cloud cover extent; general
expectations are for highs in the upper 80s each afternoon for
Indianapolis.

Tuesday and Beyond...

Surface high pressure will nudge into the area mid to late week next
week with mostly dry weather likely Wednesday onward. Temperature
are also expected to drop much closer to seasonal for the middle of
next week with highs in the mid 70s and lows in the 50s. Will have
to watch for an inverted trough just to the east, which could bring
a few showers if it ends up being farther west than expected.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 801 PM EDT Fri Sep 18 2026

Impacts:

- Showers and storms return tomorrow

Discussion:

Low FEW to SCT clouds possible through the period, but cloud decks
largely expected to stay VFR except in the storms expected to move
in tomorrow. A more organized area of showers and thunderstorms is
expected to be within central Indiana between 15-23Z tomorrow.
Greatest confidence in rainfall is at KLAF and probably KIND, but
KHUF and KBMG may also be impacted as well.

Winds will be fairly consistent out of the east through much of the
night , then veer to the SE and eventually S into tomorrow. Winds
should stay below 10kt outside of thunderstorms throughout the TAF
period.


&&

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

$$

UPDATE...Crosbie
AVIATION...KF
DISCUSSION...Updike