The gradient between a ridge over the Appalachians and a trough just west of the region, quickly ejecting to the north-northeast...resulted in a robust low level jet (LLJ) of 45-60 mph at the 850 mb level.�� Strong wind shear between the LLJ and southerly surface flow of about 15 mph combined with modest yet adequate instability, to produce multiple lines of thunderstorms from the late afternoon into the evening.�� The strongest embedded cells brought the LLJ's winds, as well as isolated large hail to the surface over northwestern central Indiana. An initial line of thunderstorms produced the majority of the damage with a bookend vortex causing the most intense damage within Attica.  A brief and stronger updraft caused 1 inch hail to fall in Montgomery county. Later, a convective line of showers with weak rotation caused additional tree damage in Clinton and Carroll counties.

Thunderstorm Wind in TIPPECANOE, INDIANA
From 11-OCT-21 16:26:00 to 11-OCT-21 16:26:00 (EST-5)
Location: PURDUE UNIVERSITY
Magnitude: 52.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A 60 mph thunderstorm wind gust was measured at WLFI. Nearby several medium to large tree limbs were snapped.

Thunderstorm Wind in TIPPECANOE, INDIANA
From 11-OCT-21 16:21:00 to 11-OCT-21 16:21:00 (EST-5)
Location: MONTMORENCIE
Magnitude: 60.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A 24 by 20 foot metal pole barn was blown down by thunderstorm wind gusts.

Thunderstorm Wind in TIPPECANOE, INDIANA
From 11-OCT-21 16:34:00 to 11-OCT-21 16:34:00 (EST-5)
Location: DAYTON
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Numerous trees blown down by thunderstorm wind gusts across the town.

Thunderstorm Wind in TIPPECANOE, INDIANA
From 11-OCT-21 16:30:00 to 11-OCT-21 16:30:00 (EST-5)
Location: LAFAYETTE ARETZ ARPT
Magnitude: 50.00 EG
Property damage: 0.50K
Crop damage: 0.00K
Reported by: Public

A 10 inch tree limb was snapped by thunderstorm wind gusts.

Thunderstorm Wind in CARROLL, INDIANA
From 11-OCT-21 17:08:00 to 11-OCT-21 17:08:00 (EST-5)
Location: YOEMAN
Magnitude: 52.00 EG
Property damage: 4.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Tree damage caused by thunderstorm wing gusts along the White and Carroll county line. There was some additional tree damage slightly to the east.

Thunderstorm Wind in CLINTON, INDIANA
From 11-OCT-21 20:24:00 to 11-OCT-21 20:24:00 (EST-5)
Location: FRANKFORT
Magnitude: 50.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: 911 Call Center

A tree of unknown size along with numerous medium to large tree limbs downed by thunderstorm wind gusts within the city limits.

Thunderstorm Wind in CARROLL, INDIANA
From 11-OCT-21 20:40:00 to 11-OCT-21 20:40:00 (EST-5)
Location: LEXINGTON
Magnitude: 52.00 EG
Property damage: 4.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Ten trees were downed across the eastern portions of the county by thunderstorm wind gusts with no specific location noted.

Thunderstorm Wind in FOUNTAIN, INDIANA
From 11-OCT-21 16:07:00 to 11-OCT-21 16:07:00 (EST-5)
Location: ATTICA
Magnitude: 56.00 EG
Property damage: 500.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Significant tree damage across the town of Attica due to strong straight line winds associated with a bookend vortex.  3 houses had damage from trees falling on them with one minor injury in one of the residences.  Near the golf course on the south side of the town, a free standing radio antenna was bent over with a noticeable amount of rust at the base.  Elsewhere, the high school lost a portion of the roof which led to water damage in the school.

Thunderstorm Wind in PARKE, INDIANA
From 11-OCT-21 15:59:00 to 11-OCT-21 15:59:00 (EST-5)
Location: ROCKVILLE
Magnitude: 52.00 MG
Reported by: Mesonet

A 60 mph thunderstorm wind gust was measured with a personal weather station.

Thunderstorm Wind in VIGO, INDIANA
From 11-OCT-21 15:39:00 to 11-OCT-21 15:39:00 (EST-5)
Location: SHEPHARDSVILLE
Magnitude: 56.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A 65 mph thunderstorm wind gust was estimated at this location. Nearby a 50 to 60 foot tree was blown down.

Hail in MONTGOMERY, INDIANA
From 11-OCT-21 16:17:00 to 11-OCT-21 16:17:00 (EST-5)
Location: NEW MARKET
Magnitude: 1.00 
Reported by: NWS Employee

Hail was reported to be slightly larger than a quarter.