textproduct: Indianapolis

KEY MESSAGES

- Hot temperatures will continue at times into Saturday, especially south. Heat indices around 100 again today southwest.

- Scattered showers and storms today, but severe storms are not expected

- Shower and storm chances persist for much of the time into next week, with temperatures turning cooler next week

FORECAST UPDATE

Issued at 1018 AM EDT Thu Sep 17 2026

Much of the forecast remain the same for today and tonight. Continuing to watch the ongoing MCS over northern Indiana this morning. The cold pool within this system is attempting to push south some, but the greatest shear remains to the north. In return weak showers are pushing into far northern portions of the area, but this should end by noon.

The forecast problem then turns to later tonight as the resulting boundary from earlier convection sinks into central Indiana. Questions remain as to exactly where this boundary will settle and how prolific if will be at initiating convection, with still a wide range in potential QPF outcomes overnight. Current expectation is for scattered convection with pockets of 1-2", but there is some higher end potential given the setup.

DISCUSSION (Today through Wednesday)

Issued at 248 AM EDT Thu Sep 17 2026

Early This Morning...

Showers and thunderstorms have been near and across the far northern forecast area early this morning. These are along a boundary, with forcing from upper energy and 850mb winds helping generate the storms. The upstream trend has been for the overall movement of the storms to shift northeast. Thus, the general threat for heavy rain has diminished for the northeast forecast area.

Will continue with some chance PoPs across the northern forecast area.

Today...

Another piece of upper energy will likely generate another round of convection north of central Indiana early, which will move southeast and impact northern portions of the forecast area this morning. Will go with likely PoPs across the extreme northern forecast area with chance PoPs across much of the remainder of the northern area.

There remains some uncertainty on how large this area of storms will be and how far south it will actually get, with latest HRRR trends being farther north. The 00Z CAM runs keep the heaviest rain north of central Indiana as well, so confidence in the Flood Watch continues to diminish. However, am reluctant to cancel the watch since a complex with heavy rain cannot be ruled out. After collaboration with neighboring offices, will just pull the southernmost county (Henry) out of the watch.

This area of storms will likely push the boundary farther southwest into this afternoon. Not much upper support will be around for convection, but can't rule out isolated convection developing. Will keep some slight chance PoPs for parts of the area.

Severe parameters indicate a very low threat for severe weather, but gusty winds and heavy rain remain possible.

The morning rain and the boundary will keep a temperature gradient across the area, with highs in the mid 80s northeast to mid 90s southwest. Heat indices around 100 will be likely again across the southwest.

Tonight and Friday...

Another round of upper energy interacting with the meandering surface boundary will bring more scattered convection. Will go with chance PoPs many areas. These will carry over into Friday morning before forcing weakens.

The boundary will get pushed farther to the southwest, so by mid- afternoon only the southwest half of the area will see any PoPs. These will be low PoPs with little or no additional forcing around.

With the expected movement of the boundary, cooler air will get into more of the area. Highs on Friday will range from around 80 northeast to the lower 90s southwest.

Saturday and beyond...

Upper and surface waves will cause the boundary to meander across central Indiana into early next week. This will keep chances for showers and thunderstorms around. Confidence on timing and location of the highest PoPs remains low with uncertainties on exact movements of the boundary.

Saturday's highs will rebound as the boundary gets pushed northeast, with lower and middle 90s southwest and mid and upper 80s northeast. However, by Monday, the boundary will be far enough south for highs in the mid 70s north to mid 80s south.

Additional upper waves will keep low chances for rain around mid- week next week. Temperatures will be more seasonable with highs in the 70s to lower 80s.

AVIATION (12Z TAF Issuance)

Issued at 621 AM EDT Thu Sep 17 2026

Impacts:

- Scattered convection may move across KLAF/KIND 13Z-18Z

- MVFR fog early at KLAF with low potential for lower ceilings

- Additional MVFR conditions may develop overnight

Discussion:

Convection currently north of KLAF will move southeast and may impact KLAF and KIND in the 13Z-18Z period. However, confidence in impacts at KIND is lowering. Additional isolated convection is possible this afternoon at all sites, but odds are too low to mention at this time.

MVFR fog may continue at KLAF early, and will have to watch for the potential of nearby stratus sneaking in. These will mix out this morning.

Will have to monitor for additional convection and MVFR conditions after 04Z.

IND WATCHES/WARNINGS/ADVISORIES

Flood Watch until 2 PM EDT this afternoon for INZ031-038-040>042.