601
FXUS63 KIND 181841
AFDIND

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

.KEY MESSAGES...

- Scattered severe storms late this afternoon and evening with
  damaging winds and localized flooding as the primary concerns

- Dry Sunday and Monday but upper level smoke will spread over the
  area

- Growing concern for numerous strong to severe thunderstorms Monday
  night with all hazards possible

- Strong to Severe storms possible again Tuesday afternoon/evening

- Noticeably cooler and less humid for the middle to latter part of
  next week behind a cold front

&&

.DISCUSSION (This Evening through Saturday)...
Issued at 241 PM EDT Sat Jul 18 2026

Convection has been a bit more plentiful than originally thought
over the last couple hours across southeast counties in the vicinity
of a remnant outflow boundary. Majority of the activity is already
shifting out of the forecast area with dry conditions elsewhere. 18Z
temperatures were in the upper 80s and lower 90s over much of the
area.

A cold front will move south across central Indiana this evening
bringing a risk for severe weather as a robust convective line
pushes through. A drier and slightly cooler airmass will overspread
the region for Sunday and Monday as high pressure passes through the
Great Lakes. Return flow will pull moisture back north into the Ohio
Valley Monday night ahead of a second stronger cold front with
increasing signals for a convective cluster producing heavy rainfall
and severe weather to move across the area Monday night into
Tuesday. In the wake of this feature...noticeably cooler and less
humid air will advect into the region for the middle and latter part
of next week.

Rest of This Afternoon through Sunday Night

Strongly unstable airmass present over the forecast area this
afternoon. Convective temps near 90 have already been reached with
isolated convection over parts of central Indiana. Focus however is
on rapidly developing convection over the lower Great Lakes in
advance of the aforementioned cold front. With sufficient deep layer
shear in the vicinity of the front expect further expansion of
convection as the line drifts south through the late afternoon and
early evening. Damaging winds remain the primary concern as DCAPEs
are progged to peak from 1000-1200 j/kg. Dry adiabatic flow persists
below 700mb into the evening but mid level lapse rates are not as
impressive...which would likely trend the convective regime towards
a loosely organized multicellular mode with scattered pockets of
damaging winds versus more widespread coverage. A Severe
Thunderstorm Watch has already been hoisted over northern Indiana
with an expectation that additional watches will be issued later on
into parts of the forecast area.

Expect storms to arrive over far northern portions of the forecast
area between 20 and 22Z then progress south across the region
through the evening and into the early overnight. Besides the wind
risk...torrential downpours and the potential for localized flash
flooding will exist despite storm motions likely to be at 25 to 30
mph. PWATs south of the boundary will hover near 2 inches with
freezing levels in the 15-16kft range aiding in highly efficient
rainfall rates. Areas particularly susceptible are locations that
received heavy rainfall on Friday afternoon and evening...
particularly across Tipton and northern Hamilton Counties.

Rain will move out of the area after 06Z with clouds gradually
diminishing as drier air advects in from the north. The passage of
high pressure to the north will provide a 36-42 hour window of dry
weather for the region along with a slightly cooler and less humid
airmass. The northerly flow that will come with the high will
however introduce another issue and that is a return of the wildfire
smoke in the upper levels of the atmosphere from the fires in
Canada. While overall levels are not likely to be as significant as
they were Thursday and Friday to our northeast but at the same
time...the smoke aloft should progress further to the southwest and
across much of the forecast area later on Sunday and into Monday and
give a hazier look to the sky. Air Quality Alerts are in effect for
all but far southern portions of central Indiana for both days to
account for the smoke impacts. Return flow on the back side of the
high by Monday afternoon will push the smoke back north.

The retrogression of the upper ridge back into the Rockies and
central Plains will place the region on the periphery of the ridge
early next week and in a susceptible location for convective
impacts. The presence of the high in the area through late day
Monday will mitigate those concerns initially but once it
departs...focus shifts to a potent upper wave riding over the top of
the ridge. This feature will dive southeast across the Great Lakes
Monday night in tandem with a surface low over James Bay and an
associated cold front extending back into the upper Midwest. Strong
signals continue to breed confidence in an MCS developing over the
upper Mississippi Valley late Monday and diving southeast towards
the region Monday night. While there remain differences with respect
to the actual evolution and track of a convective cluster...the
presence of a surface wave along the boundary will promote an
enhancement of speed and directional shear in addition to higher SRH
values. The greatest risk from an MCS moving into the region will
likely be damaging winds especially should a mature cold pool
develop. The increase in shear and SRH however would put all severe
risks in play. The orientation and strength of the low level jet in
tandem with a rapid influx of deep moisture and PWATS near 2 inches
supports heavy rainfall and flooding concerns as well. Rainfall
rates yet again should also be efficient with the freezing level
near 15kft. As is typical with mature MCSs...expect prolific
lightning rates as well.

Tuesday and Tuesday Night...

There exists substantial agreement in the deterministic models
regarding the late Monday night into early Tuesday morning MCS
moving into central Indiana associated with a fairly strong
shortwave trough /by mid summer standards/ moving through the Great
Lakes region. In the wake of the morning convective cluster
significant uncertainty exists regarding the degree of
destabilization. GFS is advertising 2000-3000 J/KG of SBCAPE by
afternoon. Given the kinematic environment, if this instability
verified, then central Indiana would be under a significant severe
threat Tuesday afternoon. Day 4 slight risk includes much of central
Indiana with this scenario in mind. It is likely that the true
degree of severe weather threat will not be known for at least
another 1-2 days given the aforementioned uncertainties in morning
convection and stability influences. The primary cold front
associated with the shortwave is expected to move through the region
during the evening...ending any threat for convection/precip.

Wednesday through Thursday...

In the wake of the Tuesday evening cold front, high pressure over
the northern plains will shift southward into the mid MS valley and
Great Lakes through Thursday. 850 mb temps average around 12-13C
both Wednesday and Thursday so highs in the mid-upper 70s and lows
in the 50s for portions of central Indiana look very likely during
the period. Definitely a change from the recent hot/humid weather.

Friday and Saturday...

As high pressure moves slowly east and weakens Friday, expect return
S-SW flow to aid in highs warming back to near normal into the 80s.
WAA and broad NW mid-upper level flow will lead to some potential
for showers/TS to develop by early next weekend. Given the time of
year and innocuous at best predictability of mid-upper level forcing
features, very low PoPs will be forecast for now.

&&

.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/e 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.

&&

$$

AVIATION...Ryan
DISCUSSION...Crosbie/Ryan