194
FXUS63 KIND 150712
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
312 AM EDT Sat Aug 15 2026

.KEY MESSAGES...

- Strong to severe storms with damaging winds, heavy rainfall, and
  flash flooding remain a significant threat through the weekend

- Heat index values in excess of 100 possible today and Sunday in
  southern portions of central Indiana

- Dry and milder weather early in the work week

- Additional storms possible Wednesday

&&

.DISCUSSION (Today through Friday)...
Issued at 312 AM EDT Sat Aug 15 2026

Through 7AM:

Rapid convective development is occurring upstream from central
Illinois westward along and north of a quasi-stationary front at the
nose of a 30-40KT southwesterly low level jet. This activity will
expand and push eastward through daybreak, likely making it into
northwestern portions of the forecast area. Modest effective shear
values and weak mid-level lapse rates suggest very limited severe
potential.

The atmosphere across the region remains deeply and anomalously
moist, however, with precipitable water values near the top end of
the climatological envelope. Highly efficient rainfall rates
continue to be a concern, owing to this deep moisture, and deep warm
rain processes, as freezing levels remain at or above 15,000 feet.
Needless to say, much of central Indiana, particularly central and
northern portions of the area, remains waterlogged tonight, and any
additional convective rainfall will rapidly pose a flash flood
threat.

7AM through Noon:

The aforementioned convection will continue to push across the area
through the morning hours, with CAMs suggesting the northern half to
two thirds of central Indiana likely to see additional
storms/rainfall. Primary concerns will be heavy rain and isolated
strong to damaging wind gusts, but due to strong low level shear an
isolated tornado cannot be ruled out entirely.

Noon through Saturday night:

Additional diabatic pressure losses over northern Indiana throughout
the day will continue an MCV with a SE progression this afternoon.
This will likely lead to additional convection NE of the I-74
corridor with isolated damaging wind gusts possible once again.
Given the orientation of this newly formed MCV to the low level jet,
training thunderstorms will be possible with a moderate (level 3 of
4) risk for excessive rainfall. This area will have very low flash
flood guidance values due to prior rainfall and therefore flash
flooding will likely have an extremely rapid onset. There is some
uncertainty with the specific placement of the precipitation axis
with the afternoon rainfall, with the best case scenario keeping the
precipitation axis north and east of the highly vulnerable region -
recent high resolution model runs are somewhat less promising in
this regard, however.

Once the MCV exits the region, height rises once again should limit
convection, keeping any rainfall mostly as a light shower during the
Saturday evening hours. That said, the heavy rainfall threat will
sadly not be over, as the nocturnal LLJ is expected to ramp up again
late Saturday night with moderate isentropic lift and additional
scattered to numerous convective showers and thunderstorms.

In additional to the rainfall mentioned earlier, southerly winds
will bump temperatures up over the south and southwest portions of
the state, especially where cloud cover will be less abundant. This
is expected to create a window of 100-106 heat index values Saturday
and Sunday afternoon along and south of a line from Sullivan to
Bloomington to Seymour and thus a Heat Advisory has been issued for
this area from 11AM today until 8PM Sunday.

Sunday and Sunday Night...

Northwest flow aloft will continue into the latter portion of the
weekend, with one or more upper level disturbances passing through
the area bringing continued threats for thunderstorms and heavy
rainfall. Extension of the ongoing flood watch into Sunday may
eventually be needed but will forgo this for now with the pressing
concern of ongoing threats and potential additional flash flooding
today at top of mind.

Instability will again be very strong in an extremely moist airmass,
though deep layer shear will be more modest. The gradual passage of
a cold front during the mid to late day hours along with enhancement
from any additional potential MCVs will serve to focus possible
severe potential along with additional heavy rainfall and flash
flooding threats. The primary severe threat would be damaging winds,
though again an isolated tornado cannot be entirely ruled out. The
more significant and pressing threat will remain flash flooding
given the extreme amounts of rainfall this week and extreme
sensitivity to additional high rainfall rates with convection.

Monday and Tuesday...

An area of surface high pressure will mercifully bring at least a
temporary end to the repeated rounds of thunderstorms early in the
week, with dry weather and near normal temperatures likely early
Monday into late Tuesday.

Wednesday...

Unfortunately, an additional round of thunderstorms appears likely
Wednesday into Wednesday night as another cold front and upper level
wave accompanying a strong jet streak aloft passes through the
region. Plentiful moisture will be available, though precipitable
water values may be slightly more modest (70-80th percentile
climatologically). However, somewhat stronger deep layer shear may
be available. Another round of severe storms will certainly be
possible, though predictability is greatly limited given the
sensitivity to prior rounds of storms and model inconsistencies 5
days out.

That said, even with a couple of days to dry out, flash flood
vulnerability will remain quite high in the face of any additional
convective rainfall given the extreme antecedent conditions, and we
will need to remain vigilant through at least mid week for these
concerns.

Thursday Onward...

Amplification of the upper ridge over the western CONUS and
southward displacement of both the frontal zone and deeper moisture
by surface high pressure and upper level troughing suggest milder
temperatures and mostly dry conditions late week and into the
weekend, though some slight chances for showers or storms may linger
across the southern portions of central Indiana. It will take quite
some time for antecedent conditions to significantly improve,
unfortunately, and any additional convective rainfall with periodic
frontal passages or upper level waves in the broader cyclonic flow
next weekend and into the following week will pose at least modest
flash flood threats.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 128 AM EDT Sat Aug 15 2026

Impacts:

- Thunderstorms likely at all sites in the 10-19Z time frame
  depending upon the site, earlier in the north and later in
  the south

- Patchy MVFR fog possible near daybreak where convection has
  not yet impacted

Discussion:

Moist low levels may promote some patchy fog development near
daybreak at sites where convection has not yet reached.

Thunderstorms are developing upstream and are expected to progress
into central Indiana late tonight into the midday hours on Saturday.
Will carry TEMPO groups at all sites during the most likely hours
for storms, though it is possible that training occurs and multiple
rounds impact the sites. Periods of MVFR or worse conditions may
occur with the storms, though fluctuations are likely. Ceilings may
be MVFR for a time in the wake of the activity before returning to
VFR.

Winds will be calm to light and variable overnight, becoming more
southerly and then southwesterly with time. Winds are likely to
again go light and variable Saturday evening.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for INZ021-028>031-035>049-
051>057-065.

Heat Advisory from 11 AM this morning to 8 PM EDT Sunday for
INZ060>063-067>071.

&&

$$

AVIATION...Nield
DISCUSSION...Nield/Updike