textproduct: Indianapolis

KEY MESSAGES

- Heat Advisory extended into Saturday afternoon for the central and southwestern half of central Indiana.

- Isolated to scattered thunderstorms will be possible at times late today through Saturday.

FORECAST UPDATE

Issued at 946 PM EDT Fri Sep 4 2026

Isolated convection has ended across central Indiana with loss of heating. The old outflow boundary in the eastern Indy metro has become more diffuse. Most clouds have dissipated.

Guidance continues to indicate convection developing northwest of the forecast area overnight and moving southeast and either clipping the northeast forecast area or moving into the northern forecast area. This is at least plausible with energy riding around the upper ridge.

Also, some increase in 850mb flow may be just enough to interact with the old outflow boundary/boundaries to generate some convection overnight. Confidence is lower for this trigger though.

Given these, have kept the slight chance to chance PoPs over about the northeast half of central Indiana overnight.

Temperatures this evening have cooled quickly in some rural areas. Have lowered hourly temperature forecasts to account for this. Also nudged down low temperatures some in these areas. Overall a warm and muggy night remains in store for the area.

DISCUSSION (This evening through Friday)

Issued at 152 PM EDT Fri Sep 4 2026

Broad ridging centered over the Plains will amplify while slowly drifting westward. This allows a trough over the northeastern US to push into the Ohio River Valley, bringing an end to the current heat wave. The ridge, temporarily shunted west, returns next week with renewed heat and humidity. The secondary round of heat does not appear to be as prolonged, with another trough arriving late next week along with a reduction in temperatures. Scattered showers and thunderstorms are possible with both troughs, though chances are generally 40 percent or lower due to limited moisture and forcing.

Today through tonight

Temperatures are already into the mid 90s as of 1pm. Highs are once again expected to reach the mid to upper 90s with dew points in the low 70s. A Heat Advisory remains in effect as Heat Risk remains in the extreme category with heat indices around 105 degrees.

A few isolated showers and thunderstorms are possible today but overall the chances are low. Limited large-scale forcing and dryness in the atmosphere will make cumulus growth difficult. ACARS soundings show a very dry atmosphere along with a cap around 700mb. Any attempts at convective initiation will be confined to subtle features like gravity waves or horizontal convective rolls. Overall, convective chances are very low today.

Saturday

The first of the aforementioned cold fronts arrives on Saturday from the northeast. Atmospheric moisture is modeled to increase tomorrow with better lapse rates. With the front acting as an initiating force, our convective chances are a lot better compared to today. Still, large-scale mid/upper-level forcing is displaced to the northeast. Our convective chances are therefore dependent on the front itself.

Two scenarios exist. First, the front initiates convection late tonight or tomorrow morning, which then propagates southwestward into the southwesterly low-level flow ahead of the boundary. This would generally limit severe potential with the primary hazard being heavy rainfall and localized flooding.

Second, the front enters central Indiana dry allowing daytime heating to maximize. Increased instability along the front would help initiate convection during the afternoon, which would propagate southeastward in line with the shear vector. Bulk shear is not excessive, but enough to allow for some storm-scale organization into clusters or small bowing segments. Steeper lapse rates and residual dryness may present a downburst or wind threat.

In the second scenario, maximized heating may necessitate the need to expand the Heat Advisory. High-resolution guidance showing scenario two also shows high temperatures once again in the mid 90s. The only exception are locations to our northeast behind the front, with FROPA some time around noon at the IN/OH line.

SUNDAY AND MONDAY

Northeasterly flow behind the cold front brings a cool and dry air mass into the region. Temperatures fall back to near normal (low 80s for highs and low 60s for lows) along with much lower dew points. These conditions continue into early next week before the ridge begins building back in by late Tuesday into Wednesday.

AVIATION (00Z TAF Issuance)

Issued at 705 PM EDT Fri Sep 4 2026

Impacts:

- Low chances for isolated convection at times tonight - Additional scattered convection on Saturday - Wind shift to northeasterly late Saturday afternoon/evening

Discussion:

Outside of convection, VFR conditions are expected through the period.

An outflow boundary will remain not far east of KIND into this evening, and this may spark a shower or storm. Odds are low enough to leave mention out of KIND TAF. If the boundary were to make it to KIND, a wind shift to the east would occur. For now believe it will stay east of the airport. Will continue to monitor closely.

Isolated convection may be around the area late tonight into Saturday morning, with scattered convection developing Saturday afternoon. At the moment, confidence in coverage and timing is low enough to omit mention from TAFs.

A cold front will shift winds to the northeast late Saturday.

IND WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT Saturday for INZ028>030-035>037-039- 043>048-051>057-060>065-067>072.