textproduct: Indianapolis

KEY MESSAGES

- Scattered storms late this afternoon and evening with damaging winds and localized flooding as the primary concerns

- Dry Sunday and Monday but upper level smoke will spread over the area

- Growing concern for numerous strong to severe thunderstorms Monday night with all hazards possible

- Strong to Severe storms possible again Tuesday afternoon/evening

- Noticeably cooler and less humid for the middle to latter part of next week behind a cold front

DISCUSSION (This Evening through Saturday)

Issued at 241 PM EDT Sat Jul 18 2026

Convection has been a bit more plentiful than originally thought over the last couple hours across southeast counties in the vicinity of a remnant outflow boundary. Majority of the activity is already shifting out of the forecast area with dry conditions elsewhere. 18Z temperatures were in the upper 80s and lower 90s over much of the area.

A cold front will move south across central Indiana this evening bringing a risk for severe weather as a robust convective line pushes through. A drier and slightly cooler airmass will overspread the region for Sunday and Monday as high pressure passes through the Great Lakes. Return flow will pull moisture back north into the Ohio Valley Monday night ahead of a second stronger cold front with increasing signals for a convective cluster producing heavy rainfall and severe weather to move across the area Monday night into Tuesday. In the wake of this feature...noticeably cooler and less humid air will advect into the region for the middle and latter part of next week.

Rest of This Afternoon through Sunday Night

Strongly unstable airmass present over the forecast area this afternoon. Convective temps near 90 have already been reached with isolated convection over parts of central Indiana. Focus however is on rapidly developing convection over the lower Great Lakes in advance of the aforementioned cold front. With sufficient deep layer shear in the vicinity of the front expect further expansion of convection as the line drifts south through the late afternoon and early evening. Damaging winds remain the primary concern as DCAPEs are progged to peak from 1000-1200 j/kg. Dry adiabatic flow persists below 700mb into the evening but mid level lapse rates are not as impressive...which would likely trend the convective regime towards a loosely organized multicellular mode with scattered pockets of damaging winds versus more widespread coverage. A Severe Thunderstorm Watch has already been hoisted over northern Indiana with an expectation that additional watches will be issued later on into parts of the forecast area.

Expect storms to arrive over far northern portions of the forecast area between 20 and 22Z then progress south across the region through the evening and into the early overnight. Besides the wind risk...torrential downpours and the potential for localized flash flooding will exist despite storm motions likely to be at 25 to 30 mph. PWATs south of the boundary will hover near 2 inches with freezing levels in the 15-16kft range aiding in highly efficient rainfall rates. Areas particularly susceptible are locations that received heavy rainfall on Friday afternoon and evening... particularly across Tipton and northern Hamilton Counties.

Rain will move out of the area after 06Z with clouds gradually diminishing as drier air advects in from the north. The passage of high pressure to the north will provide a 36-42 hour window of dry weather for the region along with a slightly cooler and less humid airmass. The northerly flow that will come with the high will however introduce another issue and that is a return of the wildfire smoke in the upper levels of the atmosphere from the fires in Canada. While overall levels are not likely to be as significant as they were Thursday and Friday to our northeast but at the same time...the smoke aloft should progress further to the southwest and across much of the forecast area later on Sunday and into Monday and give a hazier look to the sky. Air Quality Alerts are in effect for all but far southern portions of central Indiana for both days to account for the smoke impacts. Return flow on the back side of the high by Monday afternoon will push the smoke back north.

The retrogression of the upper ridge back into the Rockies and central Plains will place the region on the periphery of the ridge early next week and in a susceptible location for convective impacts. The presence of the high in the area through late day Monday will mitigate those concerns initially but once it departs...focus shifts to a potent upper wave riding over the top of the ridge. This feature will dive southeast across the Great Lakes Monday night in tandem with a surface low over James Bay and an associated cold front extending back into the upper Midwest. Strong signals continue to breed confidence in an MCS developing over the upper Mississippi Valley late Monday and diving southeast towards the region Monday night. While there remain differences with respect to the actual evolution and track of a convective cluster...the presence of a surface wave along the boundary will promote an enhancement of speed and directional shear in addition to higher SRH values. The greatest risk from an MCS moving into the region will likely be damaging winds especially should a mature cold pool develop. The increase in shear and SRH however would put all severe risks in play. The orientation and strength of the low level jet in tandem with a rapid influx of deep moisture and PWATS near 2 inches supports heavy rainfall and flooding concerns as well. Rainfall rates yet again should also be efficient with the freezing level near 15kft. As is typical with mature MCSs...expect prolific lightning rates as well.

Tuesday and Tuesday Night...

There exists substantial agreement in the deterministic models regarding the late Monday night into early Tuesday morning MCS moving into central Indiana associated with a fairly strong shortwave trough /by mid summer standards/ moving through the Great Lakes region. In the wake of the morning convective cluster significant uncertainty exists regarding the degree of destabilization. GFS is advertising 2000-3000 J/KG of SBCAPE by afternoon. Given the kinematic environment, if this instability verified, then central Indiana would be under a significant severe threat Tuesday afternoon. Day 4 slight risk includes much of central Indiana with this scenario in mind. It is likely that the true degree of severe weather threat will not be known for at least another 1-2 days given the aforementioned uncertainties in morning convection and stability influences. The primary cold front associated with the shortwave is expected to move through the region during the evening...ending any threat for convection/precip.

Wednesday through Thursday...

In the wake of the Tuesday evening cold front, high pressure over the northern plains will shift southward into the mid MS valley and Great Lakes through Thursday. 850 mb temps average around 12-13C both Wednesday and Thursday so highs in the mid-upper 70s and lows in the 50s for portions of central Indiana look very likely during the period. Definitely a change from the recent hot/humid weather.

Friday and Saturday...

As high pressure moves slowly east and weakens Friday, expect return S-SW flow to aid in highs warming back to near normal into the 80s. WAA and broad NW mid-upper level flow will lead to some potential for showers/TS to develop by early next weekend. Given the time of year and innocuous at best predictability of mid-upper level forcing features, very low PoPs will be forecast for now.

AVIATION (00Z TAF Issuance)

Issued at 656 PM EDT Sat Jul 18 2026

Impacts:

- TSRA impacts at the terminals for a 1-3 hour period this evening

- Patchy fog possible at LAF, perhaps other sites

Discussion:

A broken line of thunderstorms is progressing to the south/southeast across central Indiana. LAF has seen plentiful rainfall and TS impacts for the last hour or two, and will continue to have some potential for the first hour or so of the period, with other sites also seeing impacts for a brief period this evening. Will carry VCTS and a TEMPO group at each site for the necessary period. Conditions will likely drop to IFR at times, but recover fairly quickly once storms pass.

Those sites receiving the most rainfall, LAF among them, will have potential for fog late tonight. Will carry a TEMPO MVFR/BCFG group at LAF. Will not do this at the other sites for now given significant uncertainty on clearing of mid and high cloud, but this is certainly a possibility as well.

VFR conditions are expected tomorrow with fair weather and northeasterly winds below 10KT.

IND WATCHES/WARNINGS/ADVISORIES

None.