textproduct: Indianapolis

KEY MESSAGES

- Showers and thunderstorms today, with isolated severe storms capable of damaging winds this afternoon and evening

- Strong post-frontal northwest winds will gust between 30 and 40 mph on Friday

- Widespread frost and localized freeze conditions are likely Saturday night into Sunday morning

DISCUSSION (Today through Wednesday)

Issued at 131 AM EDT Thu Oct 15 2026

Today through Friday.

As of early this morning, the front that brought rain to central Indiana is south of the forecast area, but as the next low pressure system moves in from the Central Plains later this morning, that front is expected to push back to the north. Ahead of the boundary, poleward moisture advection characterized by an 850 mb low-level jet of 40-50 kt will lift surface dew points into the low-to-mid 60s, creating a short window in the mid to late afternoon hours where MLCAPE could reach 750 to 1250 J/kg along and south of the I-70 corridor by early afternoon. Kinematic fields are quite robust, with 500 mb mid-level flow around 50-60 kt yielding effective bulk shear of 45-55 kt. This deep-layer shear will favor organized multi-cell clusters and linear segments capable of bowing along with an increasing threat for a few discrete supercells late this afternoon into the evening.

Low-level 0-1 km storm-relative helicity values of 100-150 m2/s2 will support an isolated brief spin-up along the warm front, but that threat will be conditional on the front location and extent of daytime warming. Thus the dominant convective hazard will be damaging straight-line downdraft winds up to 60 mph via momentum transport with the tornado threat being secondary. HREF ensemble members (HRRR, FV3, and ARW) depict initial convective development across west-central Indiana between 16Z and 18Z, progressing across the Indianapolis metro area between 19Z and 22Z, and exiting eastern counties by 01Z-02Z. QPF will average between 0.50 and 1.25 inches; localized training could produce minor nuisance ponding in poor drainage areas, but the progressive motion of the system will mitigate widespread flash flood concerns.

The cold front will push southeast of the forecast area by 03Z, bringing an end to heavier precipitation with lingering light rain through the night. Cold air advection will ensue overnight as 850 mb temperatures plummet from +12C to near +1C by Friday afternoon. The tight pressure gradient between the departing surface low over eastern Canada and a Canadian high building into the Plains will generate efficient boundary-layer momentum transfer. Diurnal mixing into the 850-800 mb layer will tap into 35-40 kt ambient flow, supporting sustained northwest winds of 18-25 mph with frequent gusts of 35-40 mph Friday afternoon. Cyclonic flow and steep low- level lapse rates will foster an extensive stratocumulus deck, particularly across the northern two-thirds of the CWA. Highs on Friday will remain suppressed, ranging from the upper 50s north to the lower 60s south. Winds Friday night should keep frost formation limited even as temperatures drop into the mid to upper 30s, but sheltered areas could see some frost ahead of a widespread frost Saturday night.

Saturday Through Wednesday.

A broad longwave trough will anchor across the eastern CONUS on Saturday as a strong surface anticyclone shifts from the Upper Mississippi Valley southeastward across the Ohio Valley through Sunday. The core of the cold pool will sit overhead Saturday, keeping 850 mb temperatures around 0C to +2C. Despite clearing skies and subsidence, daytime highs on Saturday will struggle to reach out of the mid 50s, 10-15 degrees below normal.

Saturday night into Sunday morning represents the primary frost and low-end freeze window of the period. The surface high center will settle directly over central Indiana by 09Z Sunday, decoupling the boundary layer and yielding calm winds, clear skies, and a very dry ambient air mass with dew points in the upper 20s to low 30s. Strong radiational cooling will cause overnight minimum temperatures to drop into the lower to mid-30s across the entire forecast area, with rural drainage basins and traditional cold spots likely dropping near freezing. Widespread frost is expected across central Indiana, and freeze conditions are probable in sheltered rural areas. Frost and freeze headlines will likely be required as confidence remains high across deterministic GFS, ECMWF, and their respective ensemble suites.

The anticyclone will drift eastward toward the Mid-Atlantic on Sunday, allowing insolation to rebound highs into the upper 50s and lower 60s. Lows Sunday night will remain cool, in the upper 30s to lower 40s, with patchy frost confined to far eastern rural valleys before low-level winds back to the south.

For Monday through Wednesday, the synoptic pattern transitions as upper-level ridging builds over the eastern states and a deep trough carves out over the western CONUS. Steady south-southwesterly return flow will drive a significant warm air advection regime across the Ohio Valley. 850 mb temperatures will moderate to +10C to +13C, pushing daytime highs into the lower 70s on Monday and mid-70s on Tuesday. Overnight lows will moderate into the upper 40s to mid-50s.

Medium-range guidance indicates an ejecting northern-stream shortwave trough will drag an associated surface cold front toward the Lower Great Lakes and Ohio Valley Tuesday night into Wednesday. Moisture convergence ahead of this boundary will raise precipitable water values back above 1.25 inches, supporting chance to likely PoPs for rain showers and isolated embedded thunderstorms late Tuesday night through Wednesday afternoon. Displaced upper-level dynamic support and marginal instability currently suggest a low probability of severe weather with this mid-week frontal passage. Temperatures on Wednesday will run in the upper 60s to lower 70s ahead of the front.

AVIATION (06Z TAF Issuance)

Issued at 131 AM EDT Thu Oct 15 2026

Impacts:

- MVFR to IFR cigs are expected for much of this TAF period - Showers and storms likely this afternoon, confidence highest at HUF and BMG - Additional showers tonight - Wind shifts through the period

Discussion:

MVFR to briefly IFR cigs will continue through the overnight hours ahead of the next round of rain during the afternoon hours today. Confidence is highest in the 17Z to 00Z timeframe towards BMG and HUF where both brief gusty winds and lightning are possible. Elsewhere and throughout the remainder of the TAF period, lightning potential looks low. Vsbys should remain VFR outside of stronger showers and storms. Winds will vary through the period, northeasterly tonight, southerly tomorrow afternoon, and westerly during the evening. Outside of convection, westerly winds will occasionally gust up to 20kt tomorrow evening.

IND WATCHES/WARNINGS/ADVISORIES

None.