textproduct: Indianapolis

KEY MESSAGES

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

- Scattered showers and storms, with locally heavy rain possible, will diminish this morning

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

FORECAST UPDATE

Issued at 907 AM EDT Fri Sep 18 2026

The convection overnight has reinforced a synoptic boundary pushing in from the NE. This boundary is currently just to the NE of central Indiana, but should settle to the SW of Indianapolis by early this afternoon creating a dichotomy of temperatures across the region (low 80s to the NE, low 90s to the SW). As this synoptic boundary pushes to the SW the PBL will become increasingly saturated, leading to patchy fog over NE central Indiana throughout the morning.

A lingering mesoscale boundary is still present over SW portions of the area, of which has been a catalyst for morning convection. This will continue the chances for isolated showers and storms over this area this afternoon and evening.

DISCUSSION (Today through Thursday)

Issued at 247 AM EDT Fri Sep 18 2026

Early This Morning...

Thunderstorms from late evening Thursday sent another outflow boundary into the far southern forecast area. So far early this morning, only isolated to widely scattered showers and thunderstorms have developed in the wake of this boundary.

Given the latest trends in radar and in short term guidance, will keep PoPs no higher than the chance category. As the main surface boundary continues to sink south, the highest PoPs will gradually shift south. CAPE has been diminished, so not expecting any severe storms. Gusty winds will remain possible, especially south where what CAPE is left is highest.

Advected Layered Precipitable Water data from satellite shows moisture being brought into the area from the Gulf as usual but also from both the southwestern USA in the monsoon areas. Values near 2 inches are across the area currently. Thus, the threat for locally heavy rain continues. With this threat, am hesitant to cancel the Flood Watch, even though training of heavy rain looks less likely.

Today and Tonight...

The main surface boundary will continue to sink south across the area. Little upper support will be around to work with the boundary. Thus odds of convection are low. Will only have some patchy slight chance PoPs around in the south for most of the day, but can't rule out an isolated shower elsewhere. The Flood Watch will likely be canceled early.

A good temperature gradient will exist today, with highs in the 70s northeast to around 90 in the far southwest. Heat indices in the far south will be near 100 again today.

Much of tonight looks dry with forcing remaining away from the area.

Saturday into Tuesday...

An unsettled pattern will continue for much of this period as various upper and surface waves move through, causing the front to meander north and south across central Indiana. Moisture still looks to be plentiful, so locally heavy rain will remain a threat for all or parts of the area through Monday.

On Saturday, there looks to be a low end severe threat where isolated severe storms could produce damaging winds.

Highs this weekend will vary from around 80 far north to around 90 far south.

Cooler air will work in for Monday and Tuesday with highs falling to around 70 to the lower 70s by Tuesday.

Wednesday and beyond...

Surface high pressure will nudge into the area mid to late week next week and may keep this period dry. Will have to watch for an inverted trough just to the east, which could bring a few showers if it ends up being farther west than expected. Temperatures will be much closer to normal with highs in the 70s and lows in the 50s.

AVIATION (12Z TAF Issuance)

Issued at 611 AM EDT Fri Sep 18 2026

Impacts:

- Scattered convection ending early - IFR at KLAF, MVFR at KIND, Low VFR elsewhere this morning - VFR returns to the northern sites this afternoon

Discussion:

By valid time, only a few showers should be lingering near the southern TAF sites. These will exit early in the period. Cannot rule out an isolated shower again this afternoon at KBMG, but odds are too low to include.

An area of MVFR/IFR ceilings will continue to push south as the surface front moves south. MVFR should at least reach KIND by 13Z, but there remains a lot of uncertainty on whether it makes it to the southern sites. IFR will likely continue at KLAF.

Ceilings will lift to VFR during the afternoon.

IND WATCHES/WARNINGS/ADVISORIES

Flood Watch until 10 AM EDT this morning for INZ054>057-063>065- 072.