textproduct: Indianapolis

KEY MESSAGES

- Marginally severe storms through daybreak along with potential additional flooding

- Flood Watch continues through today with additional strong to severe storms through the day, mainly during the afternoon

- Damaging winds will be the main threat today outside of flooding

- Storm chances continue through the rest of the week, severe weather threat looks lower

MESOSCALE UPDATE

Issued at 1041 AM EDT Wed Aug 12 2026

Mesoscale forcing is maximized from near Kokomo southeastward through Anderson, Muncie and New Castle where a subtle midlevel thermal/moisture gradient exist. Recent radar trends have shown and increase in convection in this area. With mean flow parallel to this, deep warm cloud layer, and anomalous moisture, training heavy rain-producing convective elements will likely continue in the near term resulting in significant flash flooding potential in this corridor.

DISCUSSION (Today through Tuesday)

Issued at 133 AM EDT Wed Aug 12 2026

Overview.

Active weather continues into today with additional rounds of showers and thunderstorms. A few storms could produce localized heavy rain and strong gusty winds this afternoon and evening with best chances across southwest Indiana. A front associated with the system will gradually move south into early Thursday with additional marginally severe storms through Friday. Rain chances generally look lower for the weekend with the jet stream further north into the Great Lakes.

Rest of Tonight.

The main focus through the remainder of the overnight hours will be additional thunderstorm development across eastern Indiana with the LLJ ramping up. Storm coverage has been gradually increasing over the last 2 hours with heavy rain being the main threat along with occasional pulses leading to small hail. General expectations are for these storms to grow upscale and move to the southeast with additional flooding from Madison County south to Decatur county. With the storms not backbuilding as much as they were initially, flash flooding should remain isolated with broader areal flooding being the main threat.

Wednesday Through Thursday.

Indiana remains locked into northwesterly flow with broad ridging across the Central Plains and broad troughing across the Great Lakes. Shortwaves within the upper level flow will continue to bring periods of showers and storms with upper-level forcing along the exit region of a 50-60 kt mid-level jet streak aloft. A weak surface front currently across northern Indiana is expected to slowly move south through the day but generally will only have minimal impacts on storm coverage timing as much of the forcing is being driven by the jet level forcing aloft.

WAA and boundary layer heating will yield MLCAPE values ranging between 2500-3500 J/kg again today, supported by steep lapse rates exceeding 7.5 C/km above the boundary layer. While 0-6 km bulk shear vector magnitudes are modest at 25-35 kt, orientation roughly 45 degrees to the initiating boundary favors mixed mode convective structures, including multicellular clusters and bowing segments. HREF 2-5 km UH probability sweeps show maximum signal concentrated across central and southern Indiana between 21Z and 03Z with storms moving in from the west. Elevated DCAPE values above 1000 J/kg suggest damaging wind gusts will be the primary severe hazard, with steep mid-level lapse rates occasionally supporting isolated severe hail. PWATs nearing 1.8 to 2.0 inches, well above the 90th percentile, will support efficient warm-rain processes and localized torrential rainfall. Ahead of the stronger storms, initiation is likely across northern Indiana during the early morning hours today, but CAMs continue to struggle with properly diagnosing the current boundaries and impacts from the front, so confidence is lower on any impacts through the morning hours.

Additional flooding looks likely, especially in areas that saw heavy rain during the overnight hours. LPMMs show pockets of 2-3 inches beyond what already fell, but confidence is very low in where this may occur with broader model spread on the location of the axis of heaviest rain. Thus, will keep the Flood Watch through 04Z and reevaluate later today.

Convection will clear the southern CWA border late tonight as the surface cold front gradually drifts into closer to the Ohio River. Forecast confidence is fairly low into Thursday with more significant model divergence on the broader synoptic pattern and how the residual front may impact conditions. North of the front, temperatures will be much cooler with highs in the upper 70s to near 80 with minimal instability, while areas to the south of the front are likely to end up near 90. The severe threat generally should be on the warmer side with any convection to the north remaining elevated.

Friday Through Tuesday.

The broad synoptic regime during the extended period will feature a transition from post-frontal surface high pressure to mid-level ridge amplification across the Central Mississippi and Ohio Valleys. The 00Z GEFS and EPS are in have decent agreement through 00Z Monday, with the ridge over the Plains strengthening and pushing the jet stream further north into the Great Lakes. Daytime highs will climb from the lower 80s on Friday to the upper 80s and low 90s by Sunday as return southerly flow returns. Rain chances generally should remain limited to just the northern counties, but even that looks low.

By Monday into Tuesday, ensemble guidance indicates a northern stream trough traversing the Canadian Prairies into the Great Lakes region, acting to flatten the mid-level ridge and push a surface cold front toward the lower Great Lakes. Guidance exhibits typical timing disparities regarding frontal passage dynamics, with the ECMWF and EPS ensemble mean slightly slower than the GFS and GEFS composite. Low-level moisture return along a re-establishing 30 kt LLJ will bring PWATs back toward 1.5-1.7 inches. Chance POPs have been maintained for Monday afternoon through Tuesday to account for scattered frontal convection driven by weak height falls and low- level convergence.

AVIATION (12Z TAF Issuance)

Issued at 706 AM EDT Wed Aug 12 2026

Impacts:

- Isolated showers or a stray storm cannot be ruled out near IND this morning along with MVFR ceilings

- Additional convection later today, confidence highest towards mid afternoon

- Fog development expected tonight, especially near LAF/HUF

Discussion:

Brief fog development will be possible through 13Z near LAF/HUF. Isolated showers or a stray storm cannot be ruled out near IND this morning along with MVFR ceilings. Additional storms are likely later today followed up by more widespread strong to severe storms in the afternoon and evening, mainly towards BMG/IND/HUF. Brief MVFR or worse conditions are possible with any thunderstorms. Outside of convection, winds will generally be south or southwesterly at 5-10kts through the TAF period.

Fog development is expected by late tonight, especially near HUF/LAF.

The LAF ASOS is currently out of service, so no AMDs are scheduled beyond typical TAF issuances due to low confidence on present weather.

IND WATCHES/WARNINGS/ADVISORIES

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