textproduct: Indianapolis

KEY MESSAGES

- Hot and humid conditions return Today and Wednesday with highs reaching the 90s

- Thunderstorm chances increase late Today through Wednesday night with localized heavy rainfall

- Shower and storm risks persist through late week along a slow- moving frontal boundary

DISCUSSION (Today through Monday)

Issued at 255 AM EDT Tue Sep 15 2026

Early This Morning through Today...

Much of today will be quiet with upper ridging still the main influence across central Indiana. Warm advection will bring in hot and humid air from the southwest, with highs in the lower and middle 90s common across the area. With dewpoints rising into the upper 60s to lower 70s, afternoon heat indices will be in the upper 90s to near 100 in some locations.

Warm mid levels will help keep convection at bay for most areas. However, some influence from upper energy moving around the ridge as well as from a baroclinic zone to the northwest could generate some convection in portions of the western and northern forecast area late this afternoon. Will have some mainly chance PoPs there.

Given the expected instability from the hot and humid conditions, cannot rule out an isolated severe storm with damaging winds. Locally heavy rain will also be a threat.

Tonight...

The baroclinic zone will sag into the northern forecast area tonight. Increasing 850mb winds, additional upper energy, and potential boundaries from earlier convection will all aid in producing some mainly scattered convection tonight.

Similar conditions to late this afternoon will persist into the evening, keeping the threat for an isolated severe storm around. Diminishing instability should end the threat overnight. High moisture content of the atmosphere will keep a threat for locally heavy rain around as well.

Wednesday...

The upper ridge will get flattened some on Wednesday, making upper flow more zonal. This will keep the baroclinic zone in the area, keeping the threat for showers and thunderstorms around. Uncertainties in where this zone will end up along and in sky cover/rain coverage leads to decent uncertainty in high temperatures. High temperatures could range from the middle 80s to middle 90s from north to south.

Thursday through Saturday...

The upper ridge will gradually shift southwest. At the surface, a front will meander across the region. These will keep the threat for showers and thunderstorms around at times, but timing of the highest PoPs remains uncertain. For now will keep PoPs in the chance category or lower.

Depending on where the front is, high temperatures will vary across the area from the lower 80s to the lower 90s, with the potential for middle to upper 90s in the far southwest depending on how far southwest the ridge gets.

Sunday and beyond...

The surface front will gradually move south of the area. This will allow cooler air to gradually filter in. Scattered convection will accompany the front, with chances lowering as the front exits. Highs will cool into the 70s for Monday with lows in the 50s.

AVIATION (18Z TAF Issuance)

Issued at 140 PM EDT Tue Sep 15 2026

Impacts:

- Occasional SW gusts to 20 kts this afternoon.

- Thunderstorms possible at KLAF this evening through midnight. Showers possible at KIND/KHUF overnight with showers becoming more likely towards 12Z.

- MVFR ceilings expected to occur at KLAF towards 12Z Wed with lower confidence of MVFR ceilings occurring at KIND/KHUF.

Discussion:

Breezy conditions will continue this afternoon with winds gusting at times close to 20 kts mainly from 210-220 degrees. Winds will decrease quickly this evening with onset of low level nocturnal inversion. Convection is anticipated to develop over portions of central IL late this afternoon before moving into northern portions of central IN (KLAF) by this evening. Coverage of thunderstorms remains uncertain so have kept PROB 30 going for -TSRA to account for this uncertainty. Elsewhere, as activity tries to build southeastward towards the Indy metro/HUF areas later tonight, expecting threat for TS to weaken substantially given closer proximity to the upper ridge centered over the SE and very poor mid level lapse rates noted on ACARs and forecast soundings. With all this said, have therefore kept only -SHRA chances in the forecast at KIND/KHUF.

There is decent agreement that ceilings will fall overnight with low level cooling and saturation associated with both convective outflow and rainfall further N-NW of central IN. Ceilings are expected to fall into the MVFR range for KLAF towards 12Z and in the lower end of the VFR range for the remainder of the TAF sites. Showers are expected to continue for much of the morning across the TAF sites in a weakly capped but weak instability regime. Although TS are possible at KIND Wednesday afternoon, confidence is too low to mention at this time given concerns with degree of low-mid level cloud cover and expected meager instability.

IND WATCHES/WARNINGS/ADVISORIES

None.