textproduct: Indianapolis

KEY MESSAGES

- Dense Fog Advisory generally near and north of the I-70 corridor through 9AM

- Heavy rain and localized flash flooding remain the primary concern today, especially across north central Indiana into the overnight

- A few severe thunderstorms are possible today with damaging wind gusts as a storm complex moves in from the west

- Additional storm chances continue Friday into Saturday

- Warmer and more humid conditions return Saturday before drier and cooler weather settles in Sunday through early next week

FORECAST UPDATE

Issued at 334 AM EDT Thu Aug 13 2026

As dew point depressions have dropped to near 0 across very saturated soils, dense fog has begun to form across much of the I-70 corridor and points to the north. Subtle WAA over the quasi- stationary front over southern Indiana is helping to increase coverage even as high clouds stream in overhead. Expect to see coverage continue to increase through daybreak before daytime heating brings an end to the fog.

A Dense Fog Advisory will be in place through 9AM to account for the ongoing and expected fog.

DISCUSSION (Today through Wednesday)

Issued at 116 AM EDT Thu Aug 13 2026

Overview.

Warm and humid weather continues today across central Indiana with additional showers and thunderstorms. Heavy rainfall will lead to a continued threat for flash flooding, particularly across north central Indiana towards the overnight where slow moving storms are likely to bring additional very heavy rain. A few storms could also produce strong to damaging wind gusts during the afternoon and evening hours. Rain chances persist into Friday and Saturday as a frontal system moves through the region. Temperatures will briefly warm into the upper 80s and lower 90s on Saturday and Sunday before a cold front pushes through. Behind this front, high pressure will bring a stretch of drier, less humid, and pleasant weather from Monday through Wednesday.

Thursday and Friday.

Central Indiana remains positioned along the northeastern periphery of a broad upper-level ridge centered over the South- Central US, maintaining NW flow aloft with embedded shortwaves traversing the region. At the surface, a quasi-stationary convective outflow boundary rests across southern Central Indiana. Latest ACARs soundings show an unseasonably moist atmospheric profile with PWAT values ranging from 2.00 to 2.25 inches, exceeding the 90th percentile for mid-August. High moisture convergence along the boundary combined with deep warm-cloud layer depths greater than 4000 meters will drive high precipitation efficiency and warm rain processes. HREF probability-matched mean guidance highlights isolated 2 to 4 inch QPF amounts where cell training occurs. Given antecedent low FFG values from recent convective rounds, a Flood Watch remains in effect across most of central Indiana

Thermodynamically, diurnal heating will yield SBCAPE values of 1500 to 2500 J/kg, though poor mid-level lapse rates of 5.5 to 6.0 C/km will limit the higher end threat for severe weather. However, effective bulk shear of 30 to 35 kts coupled with DCAPE values near 800 to 1000 J/kg will support organized cell clusters and short bowing segments. Damaging straight-line winds driven by convective downdrafts remain the primary severe threat through Thursday evening. The main threat looks to be during the late evening and early overnight hours when another quasi-stationary complex of showers and storms looks to impact central Indiana with the potential additional flash flooding. The exact location of this axis remains uncertain, but confidence is highest in a northwest to southeast band from approximately along to slightly north of the I- 74 corridor. Broadly, much of central Indiana is likely to see 1-2.5 inches but within this axis there will be the potential for pockets of 3-6 inches.

On Friday, another subtle shortwave moving through the Upper Midwest will induce low-level warm air advection and a strengthening LLJ of 25-35kts. The surface front that has helped to drive rain chances will become subtle enough to no longer be a factor in precipitation with any showers and storms instead being driven by the shortwave aloft. Overall, chances are fairly low outside of any residual boundaries from Thursdays convection.

Saturday through Wednesday.

Models have been trending to a weaker ridge over the Central Plains which will keep the pattern active over the Ohio Valley as the jet stream won't be shunted to the north further into the Great Lakes. Southwesterly boundary-layer advection will help push surface temperatures into the upper 80s and lower 90s. High dewpoints in the mid-70s will yield heat indices approaching 100 degrees across southern counties. A northern stream upper-level trough over Canada will sweep a surface cold front across the Great Lakes and Ohio Valley Sunday into Monday. Convective initiation is expected along the front as MLCAPE reaches 1500 to 2000 J/kg amid 30 to 40 kts of 0- 6 km bulk shear. Multicell lines capable of strong wind gusts and brief heavy rain will accompany the cold frontal passage.

As the surface cold front exits to the south, allowing a ~1020 mb surface high pressure system to build southward from the Canadian Prairies into the Great Lakes. Advection of air from the northwest will help to bring drier and slightly cooler air into the area late Monday through Wednesday with broadly quiet weather.

AVIATION (12Z TAF Issuance)

Issued at 631 AM EDT Thu Aug 13 2026

Impacts:

- MVFR/IFR conditions possible in fog and stratus through daybreak

- More widespread TSRA possible Thursday afternoon, potential for heavy rain during the overnight towards LAF

Discussion:

Some partial clearing of clouds, lessening wind, and wet ground from recent rains will lead to fog/stratus development through daybreak. Expect most of it to occur from 09Z to 12Z. IFR and worse is likely at KLAF, with MVFR and potentially worse elsewhere. Fog will mix out by 14Z.

Rain coverage through daybreak will likely remain limited to just HUF with lower chances at IND and BMG. Rain coverage then should be fairly low through the day before a complex of storms moves in from the west during the afternoon. Training storms then are likely tonight towards LAF with the potential for an extended period of MVFR to IFR vsbys.

IND WATCHES/WARNINGS/ADVISORIES

Flood Watch through Friday morning for INZ021-028>031-035>049- 051>057-060>065-069>072.

Dense Fog Advisory until 9 AM EDT this morning for INZ021- 028>031-035>049-051>057.