textproduct: Indianapolis

KEY MESSAGES

- Slightly elevated fire weather danger today and Friday due to low relative humidity and dry ground conditions

- Widespread rain and cooler temperatures expected Saturday night into Sunday from tropical moisture remnants

DISCUSSION (Today through Wednesday)

Issued at 134 AM EDT Thu Oct 8 2026

Today Through Friday.

An upper-level shortwave trough tracking across the Upper Great Lakes has pushed dry surface boundary south across central Indiana over the last few hours with the wind direction now generally westerly to northwesterly across the forecast area. Diurnal heating will deepen the boundary layer to around 4kft, but weaker winds at the top of the boundary layer will keep wind gusts more towards 15mph this afternoon and evening. Very dry mid-level air entraining into the boundary layer will cause minimum relative humidity values to drop into the 20 to 30 percent range during the afternoon. Combined with 10-hour fuel moisture values near 10 to 12 percent from antecedent dry conditions, slightly elevated fire weather danger is expected but the lighter winds will limit any higher-end impacts. High temperatures will top out in the upper 70s. High pressure building in behind the trough tonight will yield clear skies and light winds, favoring strong radiational cooling with overnight lows dropping into the upper 40s to low 50s.

On Friday, surface high pressure shifts eastward across the eastern Great Lakes, establishing a light easterly to southeasterly low- level flow regime across the Ohio Valley. Model soundings from the GFS and ECMWF show persistent subsidence aloft keeping column moisture low, with PWATs under 0.60 inches. Mostly clear skies will allow afternoon highs to reach the mid 70s. Southeasterly return flow increases slightly Friday night as the surface high exits toward the Mid-Atlantic. Increasing upper-level cloudiness ahead of the approaching tropical system will keep Friday night lows slightly warmer, ranging from the upper 40s in the east to lower 50s in the west.

Saturday Through Wednesday.

Primary focus for the long term period centers on the interaction between a Central Plains mid-level trough and tropical moisture associated with the remnants of Hurricane Isaias. Deterministic and ensemble guidance, including the GFS, ECMWF, GEFS, and EPS, demonstrate solid consensus in the remnants traveling north into the Ohio Valley bringing abundant tropical moisture both near the surface and aloft. High temperatures Saturday will reach the mid 70s under thickening cloud cover.

Precipitation will develop rapidly late Saturday evening and peak overnight into Sunday morning as strong isentropic lift is maximized beneath the right-rear quadrant of an accelerating Great Lakes jet streak. Dynamic cooling and widespread rainfall will keep Sunday high temperatures suppressed in the upper 60s, while elevated surface dewpoints hold Sunday night lows in the upper 50s. Ensemble probabilities for 24-hour rainfall exceeding 0.75 inches exceed 70 percent across central and southern Indiana, supporting the potential for a 1.0 to 1.5 inch rainfall event if the track remains near to what the NHC is currently forecasting. There are some signs that the track may shift a bit to the southeast which will keep the axis of heavier rain focused closer to the Ohio River, but we continue to monitor the trends.

Rain will taper off from west to east Sunday evening as the tropical moisture core shifts toward the Mid-Atlantic and a mid-level dry slot moves in behind the exiting trough axis. Transient mid-level ridging and surface high pressure build in on Monday, allowing warm southwesterly flow to push high temperatures back into the upper 70s under mostly sunny skies.

By Tuesday and Wednesday, a deeper northern stream trough is forecast to amplify over the Great Lakes region, sweeping a strong cold front across central Indiana Tuesday. Cold air advection behind the boundary will bring temperatures closer to normal by Wednesday. Confidence on any precipitation with this frontal passage remains fairly low with only modest forcing with the system.

AVIATION (12Z TAF Issuance)

Issued at 605 AM EDT Thu Oct 8 2026

Impacts:

-Northwesterly gusts up to 20kt this afternoon

Discussion:

VFR conditions expected through the TAF period with clear skies and northwesterly winds. There will be a few gusts up to 20kt at IND and LAF this afternoon, mainly from 18Z to 00Z before winds drop to near calm after sunset.

IND WATCHES/WARNINGS/ADVISORIES

None.