textproduct: Indianapolis

KEY MESSAGES

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

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

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

DISCUSSION (This evening through Monday)

Issued at 1253 PM EDT Mon Sep 14 2026

Overview.

Hot and humid conditions return on Tuesday as high pressure slides off to the east and warm air streams back into Central Indiana. A stalled weather front over the region will bring periodic chances for showers and thunderstorms from Tuesday afternoon through mid to late week. High temperatures will top out in the lower to mid 90s through Wednesday before a stronger cold front clears the area over the weekend, bringing cooler and drier weather by next Monday.

Tonight Through Wednesday.

Surface high pressure drifting eastward into New England will allow low-level return flow to intensify overnight, initiating theta-e advection across the Mississippi and Ohio Valleys. Guidance from the HRRR and HREF indicates an overnight 850mb LLJ of 35-40 kt supporting upstream convection over the Upper Midwest. Remnant convective debris and weakening showers may reach northern portions of the forecast area Tuesday morning before the LLJ decays. Diurnal heating within strong return flow will drive Tuesday afternoon maximum temperatures into the lower 90s, with surface dewpoints rising into the upper 60s and lower 70s. Model soundings display steep low-level lapse rates below 700mb, yielding SBCAPE values exceeding 2000 J/kg and DCAPE above 1000 J/kg. Weak tropospheric shear will constrain storm organization, but pulse convection will carry a localized threat for damaging microburst winds into Tuesday evening. Outside of thunderstorms, gradient wind gusts up to 20 mph are expected during the afternoon hours with the mixing down of boundary layer winds.

The baroclinic zone sags southward into Central Indiana Tuesday night into Wednesday as a series of shortwave impulses ripple through mid-level westerly flow aloft. Substantial moisture transport will push PWAT values to 1.75-2.00 inches across the warm sector. Strong PVA combined with low-level convergence along the boundary will trigger periodic convective clusters overnight Tuesday and through Wednesday. Given deep warm-cloud depths and mean flow oriented parallel to the surface boundary, efficient warm-rain processes will present a risk for localized training and heavy rainfall. High temperatures on Wednesday will exhibit a sharp gradient, ranging from the upper 80s north of the boundary to the mid 90s south.

Thursday Through Monday.

The synoptic pattern through late week features strong sub-tropical ridging anchored over the southeastern states with active zonal flow across the northern tier of the CONUS. Central Indiana remains positioned along the northern periphery of the thermal ridge, keeping the quasi-stationary surface front positioned over the region. Both GFS and ECMWF deterministic solutions, along with their respective GEFS and EPS ensemble means, project elevated mid-level moisture and weak convective shortwaves continuing to generate diurnally enhanced showers and thunderstorms Thursday and Friday. High temperatures will remain elevated in the upper 80s to lower 90s with high ambient humidity.

A pattern shift occurs over the weekend as a deeper upper-level trough traverses the Upper Midwest and Great Lakes basin. The associated surface cyclone will push the cold front southward through the Ohio Valley by Saturday night. Upper-level dynamics and strengthening PVA along the trough axis will support widespread precipitation along the frontal zone. Strong post-frontal CAA will establish northwest flow in the 925-850mb layer by Sunday morning, driving a slightly cooler airmass into the region. Radiational cooling beneath building surface high pressure will lower high temperatures into the lower 80s by next Monday.

AVIATION (18Z TAF Issuance)

Issued at 1253 PM EDT Mon Sep 14 2026

Impacts:

-Easterly wind gusts to 20kts this afternoon -Wind shift to southwest tomorrow afternoon with additional gusts to 20kts

Discussion:

VFR conditions expected through the TAF period with mostly clear skies. Easterly winds will generally remain between 8 and 12kts today with a few gusts up to 20kts. Gusts will be most frequent at LAF. Winds will then shift more southwesterly towards tomorrow morning with additional gusts up to 20kts after 16Z.

IND WATCHES/WARNINGS/ADVISORIES

None.