textproduct: Indianapolis

KEY MESSAGES

- Heat Advisory in effect for all of central Indiana through late today with peak afternoon heat index values up to 108 degrees

- 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.

MESOSCALE UPDATE

Issued at 327 PM EDT Fri Sep 4 2026

Scattered convection crossing the eastern Midwest from northwest to southeast is impacting north central to east central portions of the central Indiana CWA. Fueled by over 3500 J/kg of SBCAPE, following what is presently Indianapolis' hottest day in over 4 years...mainly non-rotating cells both near Muncie and approaching Rushville have downburst potential. Mid-level lapse rates are not overly impressive but given ground truth 44 mph gust in southern Randolph County from what has become a quasi-MCS cluster now in western Ohio...recognize isolated 50-65 mph are possible, especially in Rush County cell.

Additionally, northern rotating storm approaching Logansport area from the NW is on course to impact Carroll County. Outflow boundary presently aligned from SE Howard County to NE Henry County...slowly progressing to the southwest...will be a potential area of further convective development through at least 21Z. So far flash flooding concerns have been mitigated by storm motion around 20-25 mph, with eastern Randolph County most susceptible at the moment, should additional downpours effect this 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 (18Z TAF Issuance)

Issued at 152 PM EDT Fri Sep 4 2026

Impacts:

- Low chance of an isolated shower or thunderstorm today - Better chances for showers and storms on Saturday - Wind shift to northeasterly Saturday afternoon/evening

Discussion:

Mainly VFR conditions expected through the TAF period as a cold front approaches from the northeast. Aside from a low (less than 15 percent) chance of a shower/storm today, quiet and hot weather is expected.

Shower and storm chances as the front arrives on Saturday. The best chance of storms is across the northeastern portion of central Indiana from IND to BMG. Activity should be scattered in nature, so a VCSH group was added to IND for now until timing can be refined. MVFR or worse conditions possible in any thunderstorm along with gusty winds.

The front sweeps through late Saturday afternoon or early evening. A wind shift to northeasterly is anticipated. Speeds around 10kt with gusts to as high as 20kt likely.

IND WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT this evening for INZ021-031-038- 040>042-049.

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