754
FXUS63 KIND 091659
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1259 PM EDT Sun Aug 9 2026

.KEY MESSAGES...

- Hot and humid through at least mid week, with daily chances for
  showers and storms through the forecast period

- Multiple rounds of severe storms will be possible at times from
  this evening into Wednesday night with damaging winds, heavy
  rainfall, and flash flooding the primary threats

&&

.FORECAST UPDATE...
Issued at 1015 AM EDT Sun Aug 9 2026

Fog has mixed out this morning across central Indiana, leaving
behind areas of stratus. Meanwhile, elevated smoke continues to
filter the sunshine across the area.

Upped sky cover to account for the elevated smoke that will persist
throughout the day. The patchy stratus will mix out into scattered
cumulus. Partly cloudy wording will still cover it.

Well to the west, convection continues to weaken across northern
Missouri and southern Iowa. Stronger convection was confined to
Wisconsin. An 850mb jet will continue to fuel this northern
convection, and it should move southeast. Some southern development
is likely, but uncertainty remains on how far south it will reach.

Locally, an inversion will linger aloft, which should keep a lid on
convection for much of the area this afternoon.

Delayed the start of PoPs this afternoon north based on latest
trends. With the bulk of the convection expected to stay north of
the area before 00Z, kept PoPs in slight chance category.

Left high temperatures alone for now, but will continue to monitor
to see if the elevated smoke is enough to hinder temperature rises a
bit.

&&

.DISCUSSION (Today through Saturday)...
Issued at 231 AM EDT Sun Aug 9 2026

THIS MORNING THROUGH TONIGHT...

A continued very humid airmass beneath a shallow but extremely stout
nocturnal inversion this morning should allow for the development of
areas of fog across much of the area, with patchy dense fog
possible. Any fog that develops will mix out quickly in typical
diurnal fashion in the hour or so after sunrise.

Much of today is likely to be quiet, though an isolated shower or
storm cannot be completely ruled out. Modest destabilization will
occur this afternoon, but a moderately strong cap centered at or
just above 800 mb and a lack of significant forcing for ascent
should keep a lid on precip until late in the day at the earliest.

Convection is likely to develop this morning along the nose of a
modest low level jet over the upper Midwest, and then propagating
ESE along with the aforementioned jet and a slowly retreating
surface boundary over the lower Great Lakes. This convective system
will likely serve as the focus for a potential severe threat late
today into tonight, particularly across the northern half or so of
Indiana. Intensification of this system is likely as it moves into a
diurnally destabilizing airmass through the day, and additional
development is likely along its southern flank as the cold pool
encounters the aforementioned instability, which may be substantial.
Sufficient deep layer shear will be present to support storm
organization, with damaging winds the primary threat, though some
modest veering may also support a low tornado threat.

Additionally, heavy rain and localized flooding will continue to be
a threat owing to a seasonably moist airmass and efficient rain
rates thanks to seasonably high freezing levels and deep warm rain
processes, on ground that, in spots, has received substantial rain
in the past week or so.

The window for a severe threat is broad owing to uncertainties
regarding exact storm evolution, but should encompass the evening
hours and into the overnight tonight.

Highs today will again rise into the upper 80s and low 90s across
the area, particularly as little relief from convection is expected
until late in the day at the earliest. As a result, heat index
values will peak in the mid 90s to around 100 degrees, producing at
least a low heat stress threat, particularly for vulnerable
populations. Continued high humidity will limit lows to the low to
mid 70s tonight, offering little respite from the heat.

MONDAY THROUGH WEDNESDAY NIGHT...

Heat and humidity, along with multiple rounds of possibly severe
storms, will remain a concern through Wednesday night. While the
general pattern of ridge-riding convection is apparent and fairly
seasonally classic, so is the presence of high and growing
uncertainty with each passing episode of convection, as the prior
episodes and their shifting outflows, MCVs, etc., will influence the
development of subsequent rounds of storms, and predictability of
these features is modest at best, particularly with time.

It appears that the aforementioned boundary, which will meander
across areas north of the region until it moves into the area mid
week, along with subtle upper level disturbances and broad forcing
for ascent from the jet will combine with the heat and humidity
south of the boundary to spark renewed convection somewhere north or
northwest of the area Monday afternoon which will then ESE into the
strong instability through the evening hours. Again, damaging winds
and heavy rain/flooding will be the primary threats, but an isolated
tornado cannot be ruled out.

This scenario appears likely to repeat Tuesday, with renewed
convective development occurring near or upstream and pushing into
the area during the afternoon and into the overnight, and again on
Wednesday, though the origin of the convection will likely be closer
each day as the effective surface boundary sags into the region and
is reinforced by prior convective cold pools.

The WPC excessive rainfall contains all or part of central Indiana
through day 5, which is quite reasonable given the aforementioned
factors supporting heavy rainfall and the potential for multiple
rounds of significant rainfall. HREF local probability matched means
through only 00Z Tuesday show peak rainfall totals to our north as
high as 4-7 inches, demonstrating the capacity for organized
convection to produce very heavy rainfall, and the background
setting for heavy rain will not change significantly through
Wednesday night.

Heat will continue to be a concern for all or part of the area
through at least Tuesday and perhaps into Wednesday, depending upon
storm and cloud coverage, with afternoon heat indices as high as the
low to mid 100s, especially Monday.

THURSDAY ONWARD...

Temperatures will moderate significantly late in the week and into
next weekend as the front sags south of the area, though showers and
thunderstorms will remain in the forecast through the weekend as the
boundary will remain near the region, and amplifying mid and upper
level flow will keep northwest flow in place across the area.
Hydrologic concerns could persist into the latter part of the week
as well, with some signal for additional rounds of possibly training
convection along the boundary, but the already significant
uncertainty with respect to convection will only rapidly grow with
time.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1258 PM EDT Sun Aug 9 2026

Impacts:

- Brief MVFR ceilings possible early

- Convection possible mainly overnight into early Monday

- Near LLWS conditions tonight

Discussion:

Scattered to broken cumulus will continue this afternoon, with brief
MVFR ceilings possible early before bases lift to above 3000FT.
Elevated smoke will persist, and some increase in high clouds is
expected into the night.

An isolated thunderstorm cannot be ruled out later this afternoon
into early evening mainly at KLAF, but better chances for convection
arrive overnight into Monday morning with a potential organized
cluster of storms. Confidence is not great in timing or location.
Northern sites have higher odds than southern ones. Will use PROB30s
for now.

A few gusts near 20kt are possible later this afternoon. Increasing
winds aloft will bring near LLWS conditions tonight.

&&

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

$$

UPDATE...50
AVIATION...50
DISCUSSION...Nield