669
FXUS63 KIND 111001
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
601 AM EDT Tue Aug 11 2026

.KEY MESSAGES...

- Severe storms likely today, best chances during the afternoon and
  evening

- Flood Watch today across much of central Indiana, Heat Advisory
  across the southwest

- Additional storms daily through the rest of the week, flooding
  will be the main threat

&&

.FORECAST UPDATE...
Issued at 600 AM EDT Tue Aug 11 2026

Minor adjustments made to POPs over the next few hours to lower the
coverage as storms during the overnight have struggled to develop a
cold pool and dive south and instead have remained generally
elevated and rooted more in the LLJ. That being said, there have
been some signs of a more easterly component over the last 30
minutes, so we may see a gradual transition to at least some
elevated chances for rain towards Carroll and Howard county by 12Z.
Otherwise, the forecast generally remains on track with the threat
gradually ramping up associated more with the developing convection
across eastern Iowa.

&&

.DISCUSSION (Today through Monday)...
Issued at 139 AM EDT Tue Aug 11 2026

Overview.

Severe weather is likely today with a complex of storms moving in
from the northwest. Repeated rounds of thunderstorms are expected to
continue through Wednesday night with lower chances through the
remainder of the week. Damaging winds and flooding will be the main
threats today and tomorrow. Outside of storms, heat will be a
concern today with heat index values up to 105 in southwest Indiana.

Today Through Tonight.

Central Indiana remains positioned along the northeastern periphery
of a strong subtropical ridge centered over the southern Plains,
maintaining an active northwest flow regime aloft. Low-level WAA and
moisture transport continue to stream across the region, yielding
surface dewpoints in the mid-70s and PWAT values approaching 2.0 to
2.2 inches. Strong diurnal heating will destabilize the boundary
layer today, yielding SBCAPE values exceeding 3500-4500 J/kg by
afternoon. High temperatures rising into the upper 80s to low 90s
combined with elevated humidity will create heat index values near
105 degrees, particularly across southern and central counties. A
Heat Advisory is in effect for southwestern Indiana from 12PM to
9PM.

Convective initiation and timing remain tied to subtle shortwaves
riding the ridge edge and residual boundaries from previous
storms.

00Z model guidance actually is in fairly good agreement on the
broader timing for convection through daybreak and into today, but
differ on the exact details. Broadly, there is good agreement in
initiation continuing over the next couple of hours over northern
Illinois/northern Indiana, likely along the remnant outflow boundary
from the earlier convection. Some models have this quickly growing
upscale into an MCS that dives south, but with the fairly stable
near surface, expect these storms to remain elevated and generally
sub-severe. The second round would then initiate across eastern Iowa
and northern Illinois towards mid-morning with quick upscale growth
into an MCS and an arrival near the I-74 corridor towards the late
afternoon to early evening. By the time storms arrive SB CAPE values
will be in excess of 3500 J/kg across central Indiana with
sufficient shear to maintain an organized MCS with the potential for
widespread damaging winds. If storms through daybreak do end up
growing upscale, this could delay the second round by a few hours,
but with the very humid airmass, it looks unlikely that any morning
convection would significantly lower any risk later in the day.

Regardless of timing, heavy rainfall and flash flooding will be
another significant concern. High freezing levels above 14,000
feet and deep warm-rain processes combined with the potential for
training convective cores along the western periphery of the
complex raise flash flood potential. HREF probability matched mean
guidance indicates localized rainfall totals of 2 to 4 inches
where storm training occurs. With that in mind, a Flood Watch is
in effect from 12PM through 10PM with the potential need for an
extension or additional watch for Wednesday.

Wednesday Through Monday.

The active synoptic configuration persists into Wednesday as central
Indiana stays situated in the baroclinic gradient on the eastern
flank of the southern ridge. Global guidance, including the GFS and
ECMWF, depicts a prominent mid-level trough digging from the Upper
Midwest into the Great Lakes on Wednesday. This wave will help to
push the aforementioned surface cold front southward through the CWA
late Wednesday through early Thursday morning. Deep-layer moisture
remains unseasonably high across the southern half of the forecast
area with PWATs lingering near 2.0 inches ahead of the boundary. The
combination of frontal forcing, upper-level jet divergence, and
moderate instability will generate another round of showers and
thunderstorms Wednesday afternoon and night. The GEFS and EPS
ensemble means show strong agreement on severe weather and heavy
rainfall potential continuing along and south of I-70 until frontal
passage occurs early Thursday.

By Thursday night into Friday, model guidance agrees on the southward
progression of the surface cold front into the Ohio Valley, bringing
at least some minor relief from the hot and humid conditions. High
temperatures Thursday and Friday will moderate into the low to mid-
80s with dewpoints dropping into the upper 60s to low 70s for all
but the southern portions of the state. Low-end chance PoPs are
maintained across southern counties beginning Friday morning to
account for residual elevated moisture and minor shortwave energy
overriding the frontal zone, but the overall threat for severe
weather and flash flooding will wane significantly.

For the weekend, the overall synoptic evolution diverges slightly
between deterministic operational runs. The ECMWF maintains quasi-
zonal flow aloft with surface high pressure shifting toward the East
Coast, keeping central Indiana mostly dry with temperatures near
seasonal normals. The GFS suggests a faster return of low-level warm
air advection and ridge building northward into the Ohio Valley by
Sunday, introducing isolated diurnal thunderstorm chances. EPS and
GEFS ensemble cluster analyses favor a drier consensus for Saturday
before gradually increasing PoPs across western counties late Sunday
into Sunday night.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 600 AM EDT Tue Aug 11 2026

Impacts:

- TSRA possible at times through the TAF period, confidence highest
  at LAF and IND
- Best chances currently look to be from 17Z to 00Z
- Southwesterly wind gusts up to 20kts 15Z to 00Z
- Potential for fog tonight, mainly at LAF

Discussion:

VFR conditions expected outside of convection through the TAF
period. The first chance for precipitation will be during the pre-
dawn hours towards LAF but confidence remains low that the ongoing
convection to the north will impact the site. Better chances arrive
towards the afternoon and evening hours with a bowing line of storms
which could bring damaging winds to LAF/IND. With confidence low on
timing, will limit the TSRA mention to just a PROB30 between 18Z and
00Z. As confidence on timing increases, will narrow down the windows
in later TAF issuances. Southwesterly winds will occasionally gust
up to 20kts through the afternoon before dropping closer to calm
after 00Z. Fog will be possible tonight depending on the extent of
rainfall today with confidence highest at LAF.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch from noon EDT today through this evening for INZ021-
028>031-035>049-054>057-063>065-072.

Heat Advisory from noon today to 9 PM EDT this evening for
INZ060-061-067>070.

&&

$$

UPDATE...White
AVIATION...White
DISCUSSION...White