942
FXUS63 KIND 100257
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1057 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
  tonight into Wednesday night with damaging winds, heavy rainfall,
  and flash flooding the primary threats

&&

.MESOSCALE UPDATE...
Issued at 1057 PM EDT Sun Aug 9 2026

Fairly robust convective development has occurred in the past 90
minutes over northwest Illinois along and south of a quasi-
stationary front and at the nose of a WSW 25-35KT low level jet
associated with a weak shortwave disturbance aloft. Sufficient
effective deep layer shear exists in and upstream of central Indiana
to support storm organization, with the most likely scenario being
initial supercells growing upscale into one or more line segments
that push eastward, then gradually more east/southeastward with time
through the night. Significant uncertainty exists with how far
southward the influence of the complex will extend, but roughly the
northeastern third to half of the area, along and NE of the I-74
corridor, appear to have the greatest threat for strong to severe
storms during the overnight hours.

Modest effective SRH values suggest a non-zero tornado threat, but
upscale growth will likely support primarily an isolated damaging
wind threat, and strongly supportive environmental factors (PWAT
values around climatological 90th percentile, high freezing
levels/deep warm rain processes, and possibly training convection
along the upshear flank of the system) will support a threat for
heavy rainfall and localized flooding as well. HREF local
probability matched means show potential for isolated 1-3 inch
amounts, with higher amounts possible in the strongest cores or
if/where training occurs.

CAMs continue to struggle to converge upon a solution, but generally
expecting storm threats across portions of central Indiana in the 1
AM to 8 AM time frame. Diurnal timing is unfavorable and should
support some gradual weakening with time, particularly near
daybreak, but may not entirely eliminate the severe threat.

&&

.DISCUSSION (This evening through Sunday)...
Issued at 255 PM EDT Sun Aug 9 2026

Bottom line up front...Repeated rounds of thunderstorms are expected
this week. Severe storms are possible into Tuesday, and heavy rain
and resultant flooding are possible at least into mid-week.

Rest of This Afternoon into Early Evening...

Generally quiet weather is expected for this period, with
very warm to hot and humid conditions.

Weakening convection across central Illinois at the moment should
diminish in coverage to less than mentionable by the time it reaches
the forecast area. However, will continue to monitor for the need to
add an isolated shower mention to portions of the southern two-
thirds of the area.

Across the northern third or so, additional convection may develop
to the south of the current area from northern Illinois into lower
Michigan. Have put slight chance PoPs in to cover this threat. A
strong storm with gusty winds cannot be ruled out given the
instability, but shear is weak enough that odds for severe look low.

Mid evening into Monday morning...

Focus then turns to the develop of an MCS. An 850mb jet should
initiate convection to the northwest of central Indiana, most likely
near the old outflow from this afternoon`s convection. The MCS will
then turn southeast as the 850mb flow veers during the night.

Unfortunately, high uncertainty remains on exactly where this will
occur. Given the setup, would believe that the highest chances for
rain will be north and east of the forecast area. However, as CAMs
show in their forecasts, many solutions are possible. For now, will
go high end chance PoPs northeast overnight with lower PoPs
elsewhere. As the MCS weakens Monday morning, will have chance PoPs
east and lower PoPs west.

With increasing shear and continued good instability, severe storms
are possible. Damaging winds will be the primary threat. Heavy rain
and resultant localized flooding will also be possible with
efficient rainfall processes.

Monday afternoon and night...

Higher uncertainty will exist in this period as some convective
development will depend on how tonight`s convection evolves, and
then the next round will depend on the previous round.

Some upper energy may kick off another complex of storms Monday
afternoon, again mainly northeast. Will go with chance PoPs there
and lower PoPs elsewhere. Monday night, similar conditions to
tonight will ignite another MCS which could move through the area
overnight Monday night. This one could be more into the forecast
area, so went likely PoPs northeast and lower PoPs elsewhere.

With high instability and decent shear, severe storms will once
again be possible. Damaging winds will be the primary threat, but
large hail and an isolated tornado cannot be ruled out. Heavy rain
will continue to be a threat, and will have to closely watch for
heavy rain moving over the same areas multiple times.

Looking at temperatures, if clouds from the morning MCS don`t stick
around, highs in the upper 80s to lower 90s will occur Monday. With
the high dewpoints, heat indices around 100 are possible, especially
south.

Tuesday and Wednesday...

Central Indiana will remain in northwest flow aloft, and a surface
front will remain in the area. This will keep the stage set for
clusters of showers and thunderstorms to move through. Locally heavy
rain will remain a threat and will have the potential for falling
over the same locations. Instability and shear will combine to keep
the possibility of severe storms around, especially Tuesday.
Damaging winds look to be the primary severe threat.

However, as is the case with previous days, the devil is in the
details. Uncertainty remains on the timing of the thunderstorm
clusters as well as how each around will affect the others (in terms
of cloud cover impacting instability, leftover boundaries, etc).
These will also impact which areas see the best chances for
convection as well.

Will have likely PoPs at times through this period. Initially
focusing on the northern forecast area, these will gradually shift
south into Wednesday night as the surface boundary gradually does
the same. Confidence in the specific timing remains low.

Heat will remain a potential threat, mainly Tuesday across the
south (the south has initially the lower chances for rain and cloud
cover). Heat indices may reach around 100 degrees if rain/clouds
hold off. Wednesday`s readings may be a few degrees cooler with the
increased clouds/rain chances.

Thursday onward...

The surface front will continue to move slowly south, eventually
getting south of the forecast area by the weekend. This will allow
cooler air to filter in, with highs in the upper 70s to middle 80s
Friday into the weekend.

Central Indiana will remain on the periphery of the upper high
(which will be to the south of the area by then), so energy moving
around the high will keep chances for showers and thunderstorms in
the forecast into next weekend.

There remains uncertainty on if the high can push north a bit during
next weekend, which would bring warmer temperatures than currently
forecast, especially south.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 751 PM EDT Sun Aug 9 2026

Impacts:

- Convection possible mainly overnight into early Monday and again
Monday night. Brief MVFR ceilings possible at times within storms.

- Near LLWS conditions tonight

Discussion:

Scattered to broken ceilings starting to move in this evening. An
isolated thunderstorm cannot be ruled out later this 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. Another
round of storms is possible Monday night as well.

A few gusts near 20kt are possible later this afternoon. Increasing
winds aloft will bring near LLWS conditions tonight but have not
included a mention in TAFs at this time.

&&

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

&&

$$

MESOSCALE...Nield
AVIATION...KF
DISCUSSION...50