After what had been a quiet few weeks, conditions rapidly changed on Thursday, August 18th, 2011. A favorable setup for severe thunderstorm activity, developed in the mid-section of the country. Very warm and humid air lifted northward into the region, while cooler air lingered in the western Great Lakes. The battleground between these two types of air mass, established itself from Nebraska to western Iowa, northern Kansas, and northern Missouri.
Severe thunderstorms developed during the evening and overnight hours of Thursday August 18th and 19th, 2011. Scattered supercell thunderstorms developed over eastern Nebraska and western Iowa, producing very large hail and heavy rain. This system quickly became organized and pushed from north to south down the Missouri river. Winds were estimated between 60 and 80 mph, as damage was reported across extreme eastern Kansas.

Thunderstorm Wind in LEAVENWORTH, KANSAS
From 18-AUG-11 22:06:00 to 18-AUG-11 22:06:00 (CST-6)
Location: TONGANOXIE
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm wind gusts were estimated up to 65 mph. Tree limbs were reported down.

Thunderstorm Wind in JOHNSON, KANSAS
From 18-AUG-11 22:23:00 to 18-AUG-11 22:23:00 (CST-6)
Location: OLATHE
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The ASOS in Gardner measured a thunderstorm wind gust at 59 mph.

Thunderstorm Wind in JOHNSON, KANSAS
From 18-AUG-11 22:32:00 to 18-AUG-11 22:32:00 (CST-6)
Location: OLATHE
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm wind gusts were estimated up to 60 mph.

Thunderstorm Wind in LEAVENWORTH, KANSAS
From 18-AUG-11 22:33:00 to 18-AUG-11 22:33:00 (CST-6)
Location: LORING
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm wind gusts were estimated up to 60 mph.

Thunderstorm Wind in JOHNSON, KANSAS
From 18-AUG-11 22:43:00 to 18-AUG-11 22:43:00 (CST-6)
Location: DE SOTO
Magnitude: 63.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Thunderstorm wind gust was measured at 72 mph.

Thunderstorm Wind in JOHNSON, KANSAS
From 18-AUG-11 22:34:00 to 18-AUG-11 22:34:00 (CST-6)
Location: OLATHE
Magnitude: 59.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The ASOS at Gardner measured a thunderstorm wind gust to 68 mph.

Thunderstorm Wind in JOHNSON, KANSAS
From 18-AUG-11 22:44:00 to 18-AUG-11 22:44:00 (CST-6)
Location: OCHELTREE
Magnitude: 75.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm wind gust was measured at 86 mph.

Thunderstorm Wind in JOHNSON, KANSAS
From 18-AUG-11 22:49:00 to 18-AUG-11 22:49:00 (CST-6)
Location: (OJC)JOHNSON CO EXEC
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Thunderstorm wind gusts were estimated up to 60 mph.

Hail in LEAVENWORTH, KANSAS
From 18-AUG-11 21:56:00 to 18-AUG-11 21:56:00 (CST-6)
Location: LEAVENWORTH
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in MIAMI, KANSAS
From 18-AUG-11 23:37:00 to 18-AUG-11 23:37:00 (CST-6)
Location: LOUISBURG
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Four to five inch tree limbs were reported down. Thunderstorm wind gusts were estimated up to 60 mph.

Thunderstorm Wind in LINN, KANSAS
From 19-AUG-11 00:05:00 to 19-AUG-11 00:05:00 (CST-6)
Location: BLUE MOUND
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Four to five inch tree limbs were reported down. Thunderstorm wind gusts were estimated up to 60 mph.

Thunderstorm Wind in DONIPHAN, KANSAS
From 18-AUG-11 21:23:00 to 18-AUG-11 21:23:00 (CST-6)
Location: WATHENA
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Thunderstorm wind gusts were estimated up to 70 mph.