textproduct: Indianapolis

KEY MESSAGES

- Heat index values up to 110 daily through Thursday

- Extreme Heat Warning in effect through Thursday evening

- Thunderstorm chances will increase Friday through the holiday weekend

DISCUSSION (Today through Tuesday)

Issued at 135 AM EDT Wed Jul 1 2026

Overview.

An intense heat wave will continue across central Indiana through Thursday, bringing dangerously hot and humid conditions with afternoon heat index values peaking between 105 and 110 degrees. Relief will slowly arrive over the holiday weekend and into early next week as temperatures pull back slightly, though this transition will also bring daily chances for scattered showers and thunderstorms.

Wednesday Through Thursday.

The synoptic pattern will remain dominated by a highly anomalous, expansive 595dm sub-tropical ridge anchored over the Ohio and Tennessee Valley regions. Strong large-scale subsidence and robust mid-level thermal capping, evidenced by 700 mb temperatures hovering near +12C to +15C, will effectively suppress deep vertical development and keep diurnal convection negligible. Persistent low- level south-southwesterly flow will continue to tap into a direct Gulf moisture plume, sustaining an exceptionally moist planetary boundary layer with surface dew points securely in the mid to upper 70s. In combination with intense diabatic heating, afternoon maximum temperatures in the low to mid 90s will drive peak heat index values up to 105 to 110 degrees across central Indiana. Consequently, the Extreme Heat Warning remains well justified through Thursday evening. By Thursday afternoon, a slight increase in shallow, diurnal cumulus is anticipated as low-level moisture pivots around the western periphery of the retreating ridge axis, though substantial convective initiation remains inhibited by the lingering capping inversion.

Friday Through Tuesday.

Medium-range guidance is in good agreement regarding the gradual deamplification and southward suppression of the upper-level heat dome heading into Friday and the holiday weekend. As the ridge flattens, the synoptic flow over the Great Lakes and Ohio Valley will transition to a progressive northwest flow regime aloft. This structural shift will allow a series of mid-level shortwave troughs and convective impulses to track into the region. Weakening large- scale subsidence paired with an anomalously moist boundary layer will support escalating chances for diurnal convection from Friday through Tuesday.

Given high precipitable water values and rich low-level moisture, robust thermodynamic instability will develop each afternoon. While weak deep-layer vertical wind shear will severely limit organized storm structures or widespread severe weather, this low-shear, high- CAPE environment will be highly conducive to localized pulse-type storms capable of producing intense microbursts and heavy downpours. By Monday and Tuesday, long-range model ensembles depict a more organized northern stream shortwave digging into the Great Lakes, driving a weak surface cold front southward across Indiana. While exact frontal timing discrepancies persist between the GEFS and EPS, this boundary will reinforce convective chances while providing much- needed cold air advection, bringing temperatures back down toward seasonal averages by the end of the period.

AVIATION (06Z TAF Issuance)

Issued at 135 AM EDT Wed Jul 1 2026

Impacts:

- Patchy ground fog early this morning

Discussion:

VFR conditions expected through the TAF period outside of patchy fog towards daybreak with a very humid airmass and winds dropping to near calm. Any fog that forms will dissipate by 12Z with clear to mostly clear skies expected through the remainder of the TAF period. Winds will generally be southerly at 7-12kts through tomorrow night outside of the near calm winds this morning.

IND WATCHES/WARNINGS/ADVISORIES

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