textproduct: Indianapolis

KEY MESSAGES

- Heat Advisory through 9PM today

- Greater thunderstorm coverage compared to Saturday, storms may impact afternoon and evening activities

- Damaging winds and heavy downpours will be the main threats

- Trending cooler into next week with daily chances for showers and storms

DISCUSSION (Today through Friday)

Issued at 104 AM EDT Sat Jul 4 2026

Overview.

Scattered thunderstorms are expected to develop across central Indiana this afternoon and evening, with a few storms capable of producing localized damaging winds. Warm and humid conditions will persist through the weekend. A stronger cold front is projected to move through the region mid-to-late next week, bringing more widespread rain chances and a return to seasonal temperatures.

Today Through Sunday.

The convective environment across central Indiana today will feature high thermodynamic instability paired with weak kinematic support. Water vapor imagery and 500mb charts show the sub-tropical ridge axis flattening and shifting slightly south of the Ohio Valley, allowing a weak shortwave impulse and an associated surface trough to move into northern and central Indiana.

In the near-term, we're tracking a complex of sub-severe storms slowly sliding to the southeast across northeastern Illinois and northwestern Indiana. Cloud tops are gradually warming, so expect the thunderstorms to continue to gradually weaken, but at least a few rumbles of thunder and brief heavy rain look likely for much of north central Indiana towards the late overnight.

The next round of convective initiation is expected during peak diurnal heating with highest confidence in storms generally between 19Z and 02Z. CAMs show a wide range of solutions which is typical in weakly-forced environments like this. CAMs also have underdone convective initiation, so will be bumping up POPs quite a bit and trying to focus the highest POPs where any boundaries from the storm complex to the north settles out.

Model soundings show a profile favorable for wet microbursts. MLCAPE values are forecast to reach 3000 to 3500 J/kg, driven by surface dew points in the mid-70s and ambient temperatures in the low 90s. Soundings also exhibit a well-mixed lower troposphere with 0-3 km lapse rates near 7.5 C/km and a layer of mid-level dry air, yielding DCAPE values over 1200 J/kg. With PWAT values around 2.0 inches, heavy precipitation loading is anticipated within storm cores. As these cores descend, negative buoyancy and evaporative cooling will enhance the potential for localized downbursts capable of producing straight-line winds up to 60 mph. Because 0-6 km bulk shear remains under 15 knots, storms will be slow-moving and outflow-dominant, which introduces additional uncertainty regarding storm longevity and the potential for localized heavy rainfall.

Convection coverage should increase towards the late evening hours with the loss of solar heating, but there are some signs that a more organized complex of storms may be moving east out of Illinois which could be enhanced by cold-pooling of afternoon storms. If this occurs, evening firework activities will likely be impacted with highest confidence across western Indiana. Sunday will see additional storms with similar conditions to Saturday, although the instability looks lower which will also lower the severe threat.

Monday Through Friday.

Central Indiana will remain positioned on the southern edge of a progressive northwest flow regime aloft through early next week. This pattern will keep the area susceptible to minor shortwave ripples and the remnants of convective complexes moving out of the Upper Midwest. Scattered, mainly diurnal showers and thunderstorms will remain possible Monday and Tuesday within a humid and minimally capped boundary layer.

Long-range guidance is in good agreement on a more significant pattern change by mid-week. A robust northern stream shortwave trough is forecast to dig into the Great Lakes region on Wednesday, driving a cold front southward through Indiana. This front will provide the necessary lift for more widespread showers and thunderstorms Wednesday afternoon and evening. The severity of the convective threat will depend on the exact timing of the frontal passage and available instability. Behind the front, strong Canadian high pressure will overspread the Midwest for Thursday and Friday. This will usher in a much cooler and drier air mass, bringing temperatures back into the upper 70s and low 80s and lowering dew points into the comfortable 50s by the end of the week.

AVIATION (06Z TAF Issuance)

Issued at 104 AM EDT Sat Jul 4 2026

Impacts:

- Isolated to scattered showers and thunderstorms possible tonight, mainly near KLAF

- Greater chance for storms Saturday afternoon through the early overnight hours, limited confidence on exact timing

Discussion:

A loosely organized band of shower and storms has developed across northern IL/IN. This convection will progress southeastward over the next few hours into central Indiana while gradually weakening between 07z to 12z. Included a PROB30 group for KLAF, but confidence in impacts at the other terminals is too low for a TAF mention.

A brief lull in convection is expected until the mid-late afternoon when another round of showers and storms appears likely. A TEMPO group was included for all sites, but confidence regarding exact timing remains limited. This is due to guidance struggling in these weakly forced environments. Thunderstorms may produce strong gusty winds and brief IFR or worse conditions.

Surface winds overall are expected to be out of the south-southwest and remain light

IND WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 9 PM EDT this evening for INZ021-028>031- 035>049-051>057-060>065-067>072.