textproduct: Indianapolis

KEY MESSAGES

- Thunderstorms this afternoon and early evening. Some Severe.

- Flood Watch through Wednesday across much of central Indiana, Heat Advisory across the southwest

- Additional storms daily through the rest of the week, flooding will be the main threat

DISCUSSION (This evening through Tuesday)

Issued at 233 PM EDT Tue Aug 11 2026

Surface analysis this afternoon continues to show a weak trough of low pressure stretching from northern IL across northern Indiana into OH. This area remains the focus for convective development. GOES19 shows a large thunderstorm cluster over northern Indiana, progressing to the southeast. Thunderstorms were found stretching from a LAF to Noblesville-Anderson-Muncie areas, and was sagging southward. Best instability across area remained southwest of the storms where SPC CAPE showed values over 4500 J/KG. Latest ACARS soundings show deep CAPE available. Aloft water vapor shows a short wave within the NW flow aloft over eastern IL triggering our convective cluster as the NW flow continue to stream from MT and WY to Indiana.

This afternoon and tonight...

Convection across the northern parts of the forecast area is expected to continue for the next several hours as the upper wave continues to progress east. Thunderstorms will try to sag southward somewhat, where the better instability will be located. Thus will continue to keep high pops in place in this along and south of the storms through the afternoon into the evening. Additional TSRA due to daytime heating will be possible across southwestern central Indiana and lower pops will still be needed there.

HRRR shows this wave exiting by early evening, and a worked over atmosphere should allow storms to end leading to a mainly dry evening and overnight period. Some fog will be possible near LAF due to the high dew points remaining across the area along with the lingering surface boundary. Look for overnight lows in the lower 70s and the highest pops during the evening hours.

Wednesday...

The persistent NW flow aloft is expected to remain in place on Wednesday, perhaps becoming a bit more northwesterly as yet another short wave is expected to pass across Central Indiana within the flow. Again the very warm and humid air mass will be in place allowing for plenty of moisture and pwats once again are near values 1.81 inches. Again ample CAPE will be in play also. Thus high pops will once again be used on Wednesday as this wave will pass, mainly in the afternoon. With a good amount of daytime heating available through the morning hours, high temperatures should again reach the upper 80s to around 90.

Wednesday Night through Thursday Night...

Through this time period there is very little change in the overall weather pattern. The same NW flow aloft is expected to be in place with several embedded waves within that flow poised to pass during this time period. The very warm, humid and unstable airmass will also remain. All of this will add up to continued chances for showers and thunderstorms, mainly capable of producing very heavy rain and damaging wings through the period. Continued pops will be used through the period.

Friday through Sunday Night....

More hot and humid weather is expected through the weekend along with daily chances for showers and thunderstorms. Models suggest ridging aloft over the plains will be building across Central Indiana through the weekend. A few ridge riding waves within a ring of fire type pattern will be capable of producing occasional showers and storms. Further support will come from the lower levels. Here, a frontal boundary will be lingering across Central Indiana on Friday before pushing north as a warm front on Saturday ahead of low pressure over the plains. The low will push east of Indiana on Sunday, likely dragging a cold front across Central Indiana. Forecast soundings through Sunday show plentiful moisture available through the column. All of this will again necessitate pops through the weekend. The warm air mass will result in high temperatures in the upper 80s to around 90.

Monday and Tuesday...

In the wake of the front on Monday, dry air and subsidence is shown to arrive as high pressure from the Great Lakes builds across Central Indiana. Forecast soundings show a dry column and for the first time in what seems like a long time show zero CAPE. Aloft, ridging is expected to return over the Rockies resulting in NW flow streaming across the plains into Indiana. At the moment it appears that little to no forcing will be available, this we should able to use a dry forecast at that time given the the expected surface high pressure.

AVIATION (00Z TAF Issuance)

Issued at 728 PM EDT Tue Aug 11 2026

Impacts:

- Uncertainty on storm timing through tomorrow; periodic storms expected - Low confidence threat of fog for LAF and HUF late tonight

Discussion:

Organized thunderstorm complex is south of TAF sites as of this writing, with stratiform trailing rain for a few more hours. Concerns are for redevelopment of thunderstorms in Illinois within warm advection regime atop residual outflow tonight, and this is particularly difficult to time. We have attempted to highlight most likely window for thunderstorms but this will likely need to be refined through amendments as trends continue to be monitored.

Depending on thunderstorms and residual clouds, there remains a conditional setup for fog at/near LAF and HUF, though confidence is lower than previous forecasts.

Depending on the expansiveness of storms later tonight and tomorrow morning, afternoon redevelopment is likely. Again, timing and coverage is in question so we have a broader prob30 for now. Expect adjustments to timing and we cannot completely rule out storms at any TAF sites at any time during the 30 hour forecast period.

IND WATCHES/WARNINGS/ADVISORIES

Flood Watch through Wednesday evening for INZ021-028>031-035>049- 054>057-063>065-072.