851
FXUS63 KIND 181603
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1203 PM EDT Sat Jul 18 2026

.KEY MESSAGES...

- Peak heat indices nearing 100 degrees today

- A line of showers and t-storms expected this evening and additional
  storms possible late Monday into Tuesday

- Severe thunderstorms are possible this evening, damaging wind
  gusts are the primary threat

&&

.FORECAST UPDATE...
Issued at 924 AM EDT Sat Jul 18 2026

Mostly sunny start for much of the area this morning with only a
small broken line of showers tracking across far northern portions
of the forecast area currently. 13Z temperatures were already rising
into the low 80s in many locations.

The primary focus for the morning update remains on the potential
for severe weather late afternoon and especially this evening as a
convective line tracks south in association with a cold front.
Largely quiet yet muggy weather is expected through mid afternoon
with only an isolated shower or storm within the increasingly
unstable airmass over central Indiana.

Convection already ongoing across parts of lower Michigan with the
expectation of westward development ahead of the southward moving
cold front through mid afternoon as storms interact with a strongly
unstable airmass over the lower Great Lakes and points south. Timing
remains consistent for impacts across central Indiana...with the
convective line arriving over far northern portions of the forecast
area after 21Z and progressing south through the region during the
evening and into the early overnight. Damaging straight line winds
will be the primary threat with DCAPE values comfortably within the
800-1200 j/kg range and modest lapse rates present below 700mb.
While storms should move at a decent clip...torrential downpours and
the potential for localized flash flooding will exist as PWATs south
of the boundary will hover near 2 inches with freezing levels in the
15-16kft range aiding in highly efficient rainfall rates.

Highs will likely make it to around 90 in many locales this
afternoon with max heat indices near 100 by late day. Zone and
grid updates out.

&&

.DISCUSSION (Today through Friday)...
Issued at 310 AM EDT Sat Jul 18 2026

Active weather is expected again today as well as another day with
highs near 90 and heat indices nearing 100. Can`t rule out a few
showers through the day, but the best chance of showers and storms
will come this evening along a cold front pushing southward across
central Indiana. Latest CAMs show that the timing will generally be
about 6pm to a little after midnight before fully exiting to the
south. Strong destabilization ahead of the approaching cold front
along with modest enhancement of mid-upper level flow could promote
isolated severe thunderstorms, primarily across northern portions of
central Indiana. Forecast soundings depict around 20-30 kt of
effective shear, strong instability with steep low-level lapse
rates, and DCAPE values as high as 1000 to 1300 J/KG which support
the threat. The primary convective hazard is damaging wind gusts.
The severe hail threat will be largely limited by the linear storm
mode.

Behind the front, surface high pressure will move in and bring
slightly cooler and drier air. Unfortunately, smoke from Canadian
wildfires could also return to the area for the start of the new
week.

Models continue to show a shortwave bringing additional
precipitation chances sometime late Monday through Tuesday. Behind
this system, guidance has much cooler and drier air for the latter
half of next week, with highs likely in the upper 70s to low 80s and
overnight lows potentially dropping below 60.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1203 PM EDT Sat Jul 18 2026

Impacts:

- Wind gusts to around 20kts through the afternoon
- Convective line with strong wind gusts and brief IFR and lower conditions
  impacting the terminals from north to south this evening into
  the early overnight
- VFR conditions return predawn Sunday

Discussion:

Diurnal cu developing early this afternoon in the warm and unstable
airmass across central Indiana. Isolated convection is not entirely
out of the question through the afternoon but the potential is too
low to include in the forecast at this time. Breezy westerly winds
will produce peak gusts to around 20kts at all terminals through
early this evening.

A robust convective line will develop across the lower Great Lakes
over the next few hours ahead of a cold front...pressing south
towards the region by late day. Recent guidance has slowed down the
arrival of the storms by an hour or two into central Indiana from
north to south this evening through about 06Z. The storms will carry
a risk for strong wind gusts on their leading edge along with
blinding rains that will produce IFR and lower visibilities at
times.

Drier air and N/NE flow will develop behind the frontal passage with
skies clearing into Sunday. There is potential for upper level smoke
from the Canadian wildfires to drift into the region prior to the
end of the forecast period. This could cause haze at the terminals
by Sunday afternoon and will likely need to address this possibility
with the next set of TAFs at 00Z.

&&

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

&&

$$

UPDATE...Ryan
AVIATION...Ryan
DISCUSSION...KF