textproduct: Indianapolis

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 (12Z TAF Issuance)

Issued at 614 AM EDT Tue Sep 8 2026

Impacts:

- None

Discussion:

High pressure will move south through the Mid Atlantic region today maintaining dry weather across central Indiana. Cirrus will drift across the region at times today with diurnal cu developing by midday as winds veer to S/SW. Cu will diminish near or just after sunset with light S/SE winds tonight. Mid and high level clouds will increase late tonight from convection upstream across the upper Mississippi Valley.

IND WATCHES/WARNINGS/ADVISORIES

None.