textproduct: Indianapolis

KEY MESSAGES

- Hot and humid through at least mid week, with daily chances for showers and storms through the forecast period

- Multiple rounds of severe storms will be possible at times from this evening into Wednesday night with damaging winds, heavy rainfall, and flash flooding the primary threats

DISCUSSION (Today through Saturday)

Issued at 231 AM EDT Sun Aug 9 2026

THIS MORNING THROUGH TONIGHT...

A continued very humid airmass beneath a shallow but extremely stout nocturnal inversion this morning should allow for the development of areas of fog across much of the area, with patchy dense fog possible. Any fog that develops will mix out quickly in typical diurnal fashion in the hour or so after sunrise.

Much of today is likely to be quiet, though an isolated shower or storm cannot be completely ruled out. Modest destabilization will occur this afternoon, but a moderately strong cap centered at or just above 800 mb and a lack of significant forcing for ascent should keep a lid on precip until late in the day at the earliest.

Convection is likely to develop this morning along the nose of a modest low level jet over the upper Midwest, and then propagating ESE along with the aforementioned jet and a slowly retreating surface boundary over the lower Great Lakes. This convective system will likely serve as the focus for a potential severe threat late today into tonight, particularly across the northern half or so of Indiana. Intensification of this system is likely as it moves into a diurnally destabilizing airmass through the day, and additional development is likely along its southern flank as the cold pool encounters the aforementioned instability, which may be substantial. Sufficient deep layer shear will be present to support storm organization, with damaging winds the primary threat, though some modest veering may also support a low tornado threat.

Additionally, heavy rain and localized flooding will continue to be a threat owing to a seasonably moist airmass and efficient rain rates thanks to seasonably high freezing levels and deep warm rain processes, on ground that, in spots, has received substantial rain in the past week or so.

The window for a severe threat is broad owing to uncertainties regarding exact storm evolution, but should encompass the evening hours and into the overnight tonight.

Highs today will again rise into the upper 80s and low 90s across the area, particularly as little relief from convection is expected until late in the day at the earliest. As a result, heat index values will peak in the mid 90s to around 100 degrees, producing at least a low heat stress threat, particularly for vulnerable populations. Continued high humidity will limit lows to the low to mid 70s tonight, offering little respite from the heat.

MONDAY THROUGH WEDNESDAY NIGHT...

Heat and humidity, along with multiple rounds of possibly severe storms, will remain a concern through Wednesday night. While the general pattern of ridge-riding convection is apparent and fairly seasonally classic, so is the presence of high and growing uncertainty with each passing episode of convection, as the prior episodes and their shifting outflows, MCVs, etc., will influence the development of subsequent rounds of storms, and predictability of these features is modest at best, particularly with time.

It appears that the aforementioned boundary, which will meander across areas north of the region until it moves into the area mid week, along with subtle upper level disturbances and broad forcing for ascent from the jet will combine with the heat and humidity south of the boundary to spark renewed convection somewhere north or northwest of the area Monday afternoon which will then ESE into the strong instability through the evening hours. Again, damaging winds and heavy rain/flooding will be the primary threats, but an isolated tornado cannot be ruled out.

This scenario appears likely to repeat Tuesday, with renewed convective development occurring near or upstream and pushing into the area during the afternoon and into the overnight, and again on Wednesday, though the origin of the convection will likely be closer each day as the effective surface boundary sags into the region and is reinforced by prior convective cold pools.

The WPC excessive rainfall contains all or part of central Indiana through day 5, which is quite reasonable given the aforementioned factors supporting heavy rainfall and the potential for multiple rounds of significant rainfall. HREF local probability matched means through only 00Z Tuesday show peak rainfall totals to our north as high as 4-7 inches, demonstrating the capacity for organized convection to produce very heavy rainfall, and the background setting for heavy rain will not change significantly through Wednesday night.

Heat will continue to be a concern for all or part of the area through at least Tuesday and perhaps into Wednesday, depending upon storm and cloud coverage, with afternoon heat indices as high as the low to mid 100s, especially Monday.

THURSDAY ONWARD...

Temperatures will moderate significantly late in the week and into next weekend as the front sags south of the area, though showers and thunderstorms will remain in the forecast through the weekend as the boundary will remain near the region, and amplifying mid and upper level flow will keep northwest flow in place across the area. Hydrologic concerns could persist into the latter part of the week as well, with some signal for additional rounds of possibly training convection along the boundary, but the already significant uncertainty with respect to convection will only rapidly grow with time.

AVIATION (06Z TAF Issuance)

Issued at 120 AM EDT Sun Aug 9 2026

Impacts:

- MVFR fog likely at the outlying sites, IFR possible

- Low chance for showers/storms late in the period all but BMG

Discussion:

Light winds and very humid low levels will set the stage for fog potential again tonight, with MVFR fog likely in the outlying areas. periods of IFR will be possible, mainly at LAF, though it cannot be entirely ruled out at HUF/BMG as well. Any fog will quickly mix out after sunrise.

Expect broken VFR cumulus to develop during the daytime hours. An isolated shower or storm cannot be ruled out, but the airmass should remain capped.

Upstream convection may begin to impinge upon central Indiana Sunday evening, and will carry VCSH at all but BMG for this potential, though uncertainty is high.

Winds will be calm to light and variable overnight, becoming south/southwesterly around 8-10KT gusting to 14-19KT depending upon the site Sunday afternoon. Gusts will die down in typical diurnal fashion in the evening.

IND WATCHES/WARNINGS/ADVISORIES

None.