textproduct: Indianapolis

KEY MESSAGES

- Heat index values between 105 to 110 daily through Friday

- Extreme Heat Warning in effect through Friday evening

- Thunderstorm chances will increase Friday through the holiday weekend

DISCUSSION (Today through Wednesday)

Issued at 138 AM EDT Thu Jul 2 2026

Overview.

An intense heat wave will peak across central Indiana through Friday, maintaining dangerously hot and humid conditions with afternoon heat index values pushing up to 110 degrees. The upper- level ridge will begin to suppress southward this weekend, allowing a transition to a more active, convective pattern with daily chances for scattered showers and thunderstorms alongside a gradual cooling trend into next week.

Today through Friday night.

The synoptic pattern through the end of the work week will be characterized by the persistence of a robust, highly anomalous 594 dm sub-tropical ridge centered over the Ohio Valley. Intense large- scale subsidence and strong mid-level thermal capping manifested by 700 mb temperatures remaining between +12C and +14C will continue to inhibit deep vertical moist convection through Thursday and much of Friday. A persistent low-level southwesterly wind component will maintain a steady tap into rich Gulf moisture, anchoring surface dew points in the mid to upper 70s across the forecast area. When combined with strong diabatic solar heating, maximum afternoon ambient temperatures in the low to mid 90s will yield dangerous peak heat index values ranging from 105 to 110 degrees.

Consequently, Excessive Heat Warnings remain in effect through Friday evening. By late Friday afternoon, subtle height falls on the northern periphery of the retreating ridge axis, combined with intense boundary layer destabilization, may support isolated convective initiation along localized mesoscale boundaries, though widespread storm development will remain heavily suppressed by the lingering cap. Coverage will be greatest north of the forecast area, but after 00Z, there may be some thunderstorms moving south towards central Indiana.

Saturday through Wednesday.

Medium-range and ensemble guidance show a transition in the upper- level pattern beginning Saturday as the sub-tropical ridge deamplifies and suppresses further into the Deep South. In its wake, a progressive northwest flow regime will establish itself across the Great Lakes and Ohio Valley. This transition will open the door for a series of migratory mid-level shortwave troughs and embedded convective impulses to traverse central Indiana, interacting with an unseasonably moist and unstable airmass. Precipitable water values hovering near or above 2.0 inches will fuel high afternoon CAPE values each day from Saturday through Monday. While details remain uncertain for storm coverage and timing on Saturday, confidence is highest from mid afternoon through sunset with coverage decreasing after 9PM.

Given the lack of robust deep-layer vertical wind shear, the primary convective mode through the weekend will favor pulse-type storms or loosely organized multicell clusters capable of producing localized downbursts and torrential rainfall rates. By Tuesday into Wednesday, long-range guidance depicts a more potent northern stream shortwave digging out of south-central Canada into the Great Lakes region, propelling a surface cold front across the state. This boundary will provide a focus for more organized convective development before introducing a much cooler, drier Canadian airmass. Significant cold air advection in the wake of the front will finally suppress temperatures back to near or slightly below seasonal levels by the conclusion of the forecast period.

AVIATION (12Z TAF Issuance)

Issued at 607 AM EDT Thu Jul 2 2026

Impacts:

- None.

Discussion:

VFR conditions expected through the TAF period outside of a low chance for patchy ground fog ahead of 12Z. Mostly clear skies expected through the TAF period with diurnally driven cu looking a bit more widespread this afternoon compared to yesterday. Winds will generally be southerly at 7-12kts through tonight outside of the near calm winds this morning.

IND WATCHES/WARNINGS/ADVISORIES

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