textproduct: Indianapolis

KEY MESSAGES

- Heat Advisory in effect for all of central Indiana through Friday evening with peak heat index values up to 108 are possible each afternoon

- Isolated to scattered thunderstorms will be possible at times late this week through the weekend.

DISCUSSION (This evening through Wednesday)

Issued at 254 PM EDT Wed Sep 2 2026

Strong mid/upper-level ridging over the CONUS remains in place through the end of the week, amplifying over the Plains this weekend. With the main ridge axis amplifying to our west, troughing over the northeastern US may nudge southwestward into Indiana late Saturday or Sunday. This could allow for a backdoor cold front out of the northeast, bringing an end to the current heat wave. The reprieve may not last long as ensemble guidance hints at the ridge building back eastward next week with above-average temperatures returning to the region.

In the meantime, heat and humidity continue to build over the Ohio River Valley. Temperatures have risen into the mid 90s with dew points in the low 70s. ACARS soundings out of IND show around 1500 J/Kg MLCAPE with guidance showing an increase to around 2500 J/Kg later this afternoon. The IND soundings also show a fairly deep but modest cap around 700mb. The profile overall is rather dry as well. Nevertheless, CAM guidance hints at some isolated convective development later today into the early evening. Forcing seems nebulous at best, and initiation will likely depend on subtle features such as horizontal convective rolls. Severe potential appears low, but with such a dry profile amid relatively steep lapse rates, a downburst capable of strong winds cannot be ruled out. Overall, chances of any one location experiencing convection today is low and severe convection even lower.

Thursday is similar to today with heat, humidity, and afternoon/evening storm chances. Thunderstorm potential looks to be a bit better than today due to influence from upstream convection (remnant outflow). The greatest potential exists across our northern CWA, and especially into northern Indiana. Depending on how upstream convection evolves overnight which determines the position of the outflow boundary, subsequent development may not even reach central Indiana. Isolated convection is also possible further south but chances are low. Severe potential exists in the form of strong wind gusts due to steep low-level lapse rates and high DCAPE (over 1000 K/Kg). Like today, overall chances are still low and severe potential even lower.

By Friday, the amplifying ridge to our west will allow upper flow to become more northerly. Guidance shows northeasterly surface flow over Ohio pushing a thermal gradient southwestward towards Indiana. Upstream convection may tend to ride along this gradient within the northerly flow aloft. Low-level flow over Indiana is out of the west- southwest at the time, which may encourage some west/southwestward propagation. Like with any potential late summer MCS, strong winds and flooding are the primary hazards. Activity may linger into Saturday morning, depending on how far upstream and how late it forms.

The thermal gradient then advances southwestward as a backdoor cold front on Saturday allowing temperatures to return to near average this weekend, perhaps even a bit below average.

AVIATION (18Z TAF Issuance)

Issued at 139 PM EDT Wed Sep 2 2026

Impacts:

- SW Wind gusts 16-20 KT this afternoon. - Sub 30% chances of showers/storms possible near LAF this evening and at IND tomorrow afternoon.

Discussion:

Upper ridge centered over the SE CONUS will continue to provide for VFR conditions through the period. Surface reflection of this high combined with a strengthening surface low over the plains will sustain modest SW winds this afternoon until 23Z with a few gusts approaching 20 kts.

A gravity wave noted on radar, and to a lesser extent visible satellite imagery, will move SE into central Indiana over the next few hours. This feature may aid in slightly greater cloud cover being generated between 050-100 along with a 1-2 hr period of weaker surface winds in the wake of the feature.

Recent satelitte imagery trends agree with short term computer models that a few storms may develop in central IL during the 19-22Z time period, before moving into far NW portions of central IN (near KLAF) around 23Z. A PROB30 was considering for this potential, but confidence isn't high enough to be included attm.

For tomorrow, the atmosphere looks to be slightly less capped and therefore more unstable. However, uncertainties reign supreme regarding the location of any focusing mechanism in the boundary layer. One possible scenario is that the Indy heat island will initiate showers/storms to the E-NE of the city. For now, given that's a 24-30 hr forecast, will not include a mention of VCSH/TS.

IND WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT Friday for INZ021-028>031-035>049- 051>057-060>065-067>072.