textproduct: Indianapolis

KEY MESSAGES

- Cooler temperatures through Tuesday night with highs in the low- mid 70s and lows in the 50s

- Showers and thunderstorms possible Tuesday, marginal risk of severe weather

- Showers and thunderstorms likely on Wednesday with a much greater risk of severe weather

FORECAST UPDATE

Issued at 904 AM EDT Mon Jun 15 2026

Surface analysis late this morning shows a surface ridge of high pressure stretching across the Central Plains into Indiana and Ohio. Light winds and pleasant dew points in the 50s were present. GOES19 shows some high clouds pushing into eastern parts of Indiana, but overall skies were mostly sunny. Aloft, water vapor showed a deep and broad area of low pressure over Hudson Bay. This feature was providing cyclonic flow across most of Canada, the Great Lakes and Indiana. Furthermore, this strong flow was keeping intrusions of hot and humid tropical air out of the Ohio valley.

The surface ridge is expected to remain across Central Indiana this afternoon. ACARS soundings this morning show a dry column. Water vapor shows subsidence upstream of Indiana. Convective temperatures will not be reached. Thus will continue with a mostly sunny afternoon and pleasant high temperatures in the middle to upper 70s.

DISCUSSION (Today through Sunday)

Issued at 303 AM EDT Mon Jun 15 2026

Broad troughing remains over the northern CONUS this week with multiple waves embedded within a quasi-zonal jet stream that rounds its base. The first wave may bring scattered showers and thunderstorms on Tuesday. On Wednesday, another potent wave arrives with the potential for thunderstorms and severe weather. Broad troughing persists through the week and into the weekend. Temperatures this week are expected to remain near to below normal due to the persistent troughing.

TUESDAY SEVERE WEATHER POTENTIAL

As mentioned above, embedded waves are rounding the base of the trough and one of these is expected to arrive on Tuesday afternoon. The wave helps induce cyclogenesis to our north over Wisconsin, which should allow winds to become southerly in response. Given how recently we had an air mass change (yesterday), it appears that rich moisture may not have enough time to return northward. Winds don't become southerly until tonight. However, this may be offset by steep to very steep lapse rates and sufficient synoptic-scale forcing. Model soundings show modest instability between 500-1500 J/Kg MLCAPE, lapse rates between 6-8 C/Km. Model hodographs are long and mostly straight, though some curvature exists in the lowest 3km.

A cold front extending southward from the low should act as a trigger for convection. Wind shear vectors are off parallel, so a discrete to semi-discrete storm mode is expected. With steep lapse rates and ample shear, supercells are possible, especially further northwest closer to the low itself. Most storms should not grow into supercells, but multicell clusters. Storms should weaken with eastward extent as instability diminishes.

In terms of hazards, all hazards are possible in supercells. Within the multicell clusters, strong winds and large hail will be the primary hazards. Overall, the threat appears on the low end as storm coverage is the biggest question. The best large-scale forcing looks to be just to our north, which may focus the severe threat across northern Illinois and Indiana compared to central Indiana.

WEDNESDAY SEVERE WEATHER POTENTIAL

Regarding Wednesday's severe weather potential, global models show a low amplitude shortwave rounding the base of the broader trough on Wednesday. This also enables cyclogenesis over the upper Midwest, with the resulting surface low tracking east into the Great Lakes. A potent low-level jet then develops in response to the deepening low, allowing for strong warm air and moisture advection northward. Additionally, the upper-level jet stream remains overhead. Model hodographs are long and curved, with a southeasterly mean shear vector.

A few scenarios exist regarding convective evolution. First, the strong warm moist advection may be sufficient to initiate convection Tuesday night far upstream over Iowa. This could consolidate into an MCS and propagate southeastward into the strong low-level jet and warm moist advection, aided by southeasterly shear. Damaging winds and localized flooding would be the primary hazards in such a scenario.

Second, there is no early convection and or the atmosphere recovers from earlier storms (strong low-level jet may easily allow this to happen even if there is morning convection, simply by advecting the rain cooled air mass northward). Atmospheric instability is maximized by continued strong warm moist advection and solar insolation. Thunderstorms initiate along the surface cold front over Illinois and propagate southeastward. Shear vectors perpendicular to the advancing front may allow for discrete mode initially, with potential for supercells. All hazards are possible in this circumstance. Eventually, convection would grow upscale becoming primarily a wind threat.

There are a lot of moving parts with this, and predictability is currently low to medium. Guidance still needs to properly resolve the initiating wave and surface low. Additionally, the potential for early convection is always a wild card and can substantially alter the pre-storm environment. Given the potential for a strong low, potent low-level jet and shear, severe weather appears probable. Stay tuned for updates as guidance comes into better agreement and additional details can be discerned.

AVIATION (12Z TAF Issuance)

Issued at 624 AM EDT Mon Jun 15 2026

Impacts:

- Chance of thunderstorms Tuesday afternoon after 17z.

Discussion:

VFR conditions are expected through the period.

Light northwesterly flow continues following Sunday's cold front. Some VFR ceilings around 5000 to 6000 feet remain, but are expected to gradually diminish through the morning.

As mentioned above, winds are light out of the northwest. Winds pick up a bit after sunrise gradually becoming more westerly as the high slides eastward. By nightfall, a light southwest breeze under 5kt will take hold.

A mid-level system passing to our north will drag another cold front through Indiana Tuesday afternoon. Guidance is showing scattered showers and thunderstorms along this front, which looks to arrive early in the afternoon. A Prob30 group has been added for the IND TAF to cover this possibility. All the other terminals have a similar chance of storms but it is currently outside their respective TAF periods.

IND WATCHES/WARNINGS/ADVISORIES

None.