089
FXUS63 KIND 081741
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
141 PM EDT Tue Sep 8 2026

.KEY MESSAGES...

- Heat returns today and Wednesday with peak heat indices in the
  upper 90s and low 100s Wednesday afternoon

- Strong thunderstorms possible late Wednesday; rain and storms
  continue Wednesday night into Thursday with heavy rain and localized
  flooding as the primary concern

- Cooler weather returns late week

&&

.DISCUSSION (Today through Monday)...
Issued at 252 AM EDT Tue Sep 8 2026

After a couple days with more seasonable temperatures...warmer air
will return to the Ohio Valley as ridging aloft once again expands
back into the region through midweek. The ridge will flatten on
Wednesday in response to a sharp upper trough traversing through
southern Canada. This will enable a frontal boundary to drift into
the area late Wednesday with chances for rain and thunderstorms into
Thursday as it shifts slowly south. Dry and seasonable conditions
return for late week but waves aloft riding within a largely zonal
flow will contribute to isolated to scattered convection this
weekend into next week.

Today through Thursday

Quiet early morning as the region remains under the influence of
high pressure. Cirrus was spilling overtop of the upper level ridge
centered to our west. 06Z temperatures were generally in the 60s.

The center of the aforementioned high will shift south through the
Mid Atlantic region resulting in return flow advecting warmer and
progressively more humid air into the Ohio Valley by Wednesday. The
expansion of the ridge currently centered over the southern Plains
will commence today with low level thermals supportive of highs
returning to a range from the upper 80s in the northeast to the mid
90s in the lower Wabash Valley. Higher dewpoint air will lag the
temp rises and overall humidity levels this afternoon during peak
heating will be manageable keeping peak heat indices in the lower
and mid 90s. The onset of S/SW winds will aid in diurnal cu
formation by midday particularly in the vicinity of a subtle
inverted trough that will wash out this morning across the southeast
half of the forecast area.

More humid air will advect into the region tonight and especially
Wednesday setting the stage for the hottest day of the week. The
approach of a cold front from the north may produce a compressional
heating component that could enable temperatures to overproduce on
Wednesday. The wild card will be whether any remnants of convection
or associated clouds over the upper Mississippi Valley late tonight
and early Wednesday can make it into the forecast area by midday
Wednesday and disrupt expected heating. Thermal profiles do support
low to mid 90s for highs and the increase in humidity suggest heat
indices will rise into the upper 90s and lower 100s during the
afternoon.

Scattered convection will be possible as the afternoon progresses
Wednesday but expect more coverage by the evening as the boundary
slides into the area and interacts with an axis of greater
instability bisecting the forecast area from southwest to northeast.
Initial convection Wednesday evening will carry a risk for damaging
winds in the strongest cells with modest DCAPE values at 800-1000
j/kg. A lack of BL shear along the boundary however will likely
force a more pulse intensity convective profile before storms settle
into a subsevere state Wednesday night with the focus shifting more
to heavy rain and localized flooding. The frontal boundary will slow
as it becomes near parallel to the upper flow through the night and
into Thursday with the potential for storms to traverse across the
same areas along and south of the I-70 corridor. With PWATs peaking
near 2 inches...locally heavy rainfall will be possible until the
front can shift south of the area Thursday night. 1 to 2 inches is
possible with locally higher amounts between Wednesday afternoon and
late Thursday.

Thursday Night through Monday

The cold front will shift south of the area Thursday night before
gradually washing out across the Tennessee Valley on Friday as the
boundary runs into the ridge over the southeast states. Weak high
pressure will track through the Great Lakes for late week with dry
and cooler conditions across central Indiana. Highs on Friday will
be in the upper 70s and lower 80s.

As the high shifts into New England by early Saturday...return flow
will draw the remnant moisture from the aforementioned front back
north into the region in advance of a secondary boundary over the
Upper Midwest. Forcing aloft is not overly impressive but the influx
of moisture and instability into the region will likely be enough to
generate isolated to scattered convection on both Saturday and
Sunday. Developing low pressure over the High Plains early next week
will shift a warm front into the lower Great Lakes and enable highs
to again rise into the mid and upper 80s. Scattered convection is
possible on Monday as well with more widespread rain and storms
expected by Tuesday as the low tracks into the region.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 139 PM EDT Tue Sep 8 2026

Impacts:

- Gusty SW winds around 20 kts Wednesday afternoon.
- Showers with scattered TS possible by 18Z north terminals, more
  likely after 22Z at KIND.

Discussion:

Quiet aviation weather is expected for the remainder of today into
tonight as S-SW low level winds remain generally under 10 kts under
SCT-BKN cirrus clouds. Around sunset winds will decrease and become
light southerly ahead of weak low pressure along a slowly moving
cold front to the N-NW of central Indiana. Scattered convection is
expected overnight well north of the area across Iowa into northern
IL. Ahead of this sagging cold front, SW winds will increase by
Wednesday afternoon with gusts around 20 kts expected at all
terminals except KLAF where a few showers and increasing mid level
cloud cover will arrive by early afternoon.

Still a good deal of uncertainty with regards to the amount of
convection expected across central Indiana tomorrow afternoon and
evening. This is primarily due to the amount of mid level cloud
cover expected by mid afternoon, possible scattered showers and
the combined negative effects on low level instability. For now
have added PROB30 for TS at KIND starting after 18Z with SHRA/VCTS
after 22Z, when the main frontal boundary approach will occur
along with possibly slightly higher instability amounts.

&&

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

$$

AVIATION...Crosbie
DISCUSSION...Ryan