Between 11 PM CDT on Thursday the 11th and 8 AM on Friday the 12th, two separate strong to severe quasi-linear mesoscale convective systems (MCS) punched south across roughly the northeast one-third of South Central Nebraska, primarily affecting locations east of a line from Ord to Aurora to Geneva. While both systems were similar in character, the second one packed more of a wallop, as a fairly localized area of wind damage occurred in parts of Merrick and Hamilton Counties between 600-630 AM, mainly affecting the Central City, Aurora and Hordville areas. Especially hard-hit by these early morning storms was the Willow Bend Lake area south of Central City, where several large trees were blown down, including one 90-feet tall that clipped the corner of a home. As the winds surged southward, a gust to 70 MPH was measured at the Aurora airport. No reports of wind damage were received as the leading edge of these storms continued southeast through the York and Geneva areas. This early morning MCS first entered the far northern counties of South Central Nebraska around 5 AM.
Several hours prior to the pre-dawn wind damage, an earlier MCS passed through almost the same counties, first affecting locations from Ord to Genoa around 11 PM CDT, and eventually exiting counties along the Highway 81 corridor around 2 AM. Although no severe-criteria winds or hail were reported with this first round, a peak gust of 54 MPH was measured at the Ord airport. In addition to strong winds and generally small hail, both systems dumped locally heavy rainfall. Storm total amounts were commonly 1.25-2.50 inches and locally higher, including 2.98 inches in Nance County west of Fullerton, and 2.68 inches at Wolbach.
Both systems that passed through South Central Nebraska initially organized and strengthened near the Nebraska-South Dakota border, before rolling southeast. The synoptic and mesoscale environment was supportive of regenerative MCS formation. Overnight parameters featured around 40 knots of deep-layer vertical wind shear, and 1000-2000 J/KG most-unstable CAPE, with instability fed by warm-air advection along the nose of a roughly 30 knot low level jet at 850 millibars. In the mid-levels, an active west-northwest flow was in place, containing several low-amplitude shortwaves.

Thunderstorm Wind in MERRICK, NEBRASKA
From 12-AUG-11 05:00:00 to 12-AUG-11 05:05:00 (CST-6)
Location: CENTRAL CITY
Magnitude: 61.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Wind gusts estimated at 70 MPH resulted in tree damage in Central City as well as in the Willow Bend Lake area.  The main tree damage occurred in the Willow Bend Lake area, where large tree limbs were knocked down and a 90 foot tree was uprooted, clipping the corner of the roof of a nearby home.  Boats were also pulled loose from structures on the shore.

Thunderstorm Wind in HAMILTON, NEBRASKA
From 12-AUG-11 05:12:00 to 12-AUG-11 05:12:00 (CST-6)
Location: HORDVILLE
Magnitude: 61.00 EG
Property damage: 65.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Wind gusts estimated at 70 MPH resulted in a few tree limbs of 4 to 6 inches being knocked down and an irrigation pivot being tipped over.

Thunderstorm Wind in HAMILTON, NEBRASKA
From 12-AUG-11 05:12:00 to 12-AUG-11 05:15:00 (CST-6)
Location: AURORA MUNI ARPT
Magnitude: 61.00 MG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: AWOS

Wind gust of 70 MPH was measured at the Aurora AWOS and a tree between 10 and 12 inches in diameter was uprooted in town.

Hail in VALLEY, NEBRASKA
From 11-AUG-11 23:18:00 to 11-AUG-11 23:18:00 (CST-6)
Location: ORD
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager