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

FORECAST UPDATE

Issued at 834 PM EDT Mon Sep 14 2026

Higher dewpoints returned across central Indiana late today ahead of increasing chances of showers later tonight. Midwest now transitioning from brief period of seasonably milder conditions to more of the same August-like warmth/humidity with zonal subtropical ridge on tap to arrive from southern Plains. For the near term, weak mid-level wave between exiting surface high and approaching warm ridge will twist from Middle MS Valley and up OH Valley... bringing enough lift to push a cluster of scattered/numerous RWs from far southern zones around 06Z to eastern counties by daybreak. Embedded thunder is on the table, with no severe cells expected. At least patchy fog is favored over mainly southern central Indiana where low 70s-dewpoints will continue to expand. Minimum temperatures by early Saturday are expected to range from 65F in Carroll County to 68F inside I-465 and across most southern zones.

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 (00Z TAF Issuance)

Issued at 653 PM EDT Mon Sep 14 2026

Impacts:

- VFR expected this TAF period

Discussion:

VFR Conditions will be expected this TAF period. High pressure centered east of our area will continue to slowly exit east overnight. A strengthing surface pressure gradient will allow winds to remain around 5-10 knts overnight. This with low dew points across the area will prevent fog formation. Thus only a few passing high clouds as seen on GOES19 will be expected. Cigs should remain unlimited.

On Tuesday, the surface high will continue to drift east as a cold front approaches from the northwest. Forecast soundings through the day continue to show a very dry layer within the lower levels and this should prevent CU for much of the day, leading to VFR conditions. Some chances for rain will be possible at IND after 00Z Wed as the cold front arrives and saturation is noted within the mid levels.

IND WATCHES/WARNINGS/ADVISORIES

None.