EF1 tornado in Dawson County, Nebraska

This tornado was witnessed by many as it formed on the east side of Cozad, where some tree damage and power poles were broken. The nearly 10-mile path weaved to the northeast across a rural landscape. One-half of a large farm machinery shed was complete destroyed and several irrigation pivots were upset, helping delineate the path. Grain bins were destroyed and tree damage was sporadic along the path. The tornado was reported to be rain-wrapped at times. The path become indiscernible as the tornado moved into the hills north of Cozad and the road network became more sparse. The estimated maximum wind speed was 100 MPH.

A long-lived supercell produced 3 weak tornadoes over Dawson county on this Friday evening. Around 2 PM CST, a north-northwest to south-southeast broken line of showers and thunderstorms developed from near Lexington to Alma and into north central Kansas. Between 2 and 430 PM CST, this line moved northeast across south central Nebraska. The strongest storms developed over Gosper and Dawson counties and moved north-northeast across Sherman and Valley counties. These storms produced some low-end severe hail (nickel to quarter size) over eastern Dawson and western Buffalo counties, and downburst winds were strong enough to knock a tree onto a lean-to south of Ord. Storms in the rest of the line rapidly weakened. Meanwhile, a lone supercell had formed over northwest Kansas. This storm moved north-northeast and crossed western Dawson county between 545 and 745 PM CST, producing three tornadoes. Two tornadoes had a maximum damage intensity of EF-1. These tornadoes were near Farnam and Cozad. The third tornado was an EF-0 west of Eddyville. The Cozad tornado was the longest with a 10-mile path. This supercell also produced severe hail from Farnam north to Gothenburg, the largest of which was the size of tennis balls in Farnam.

This was a much-anticipated day for storm chasers as the setup was classic. Deepening low pressure was over northeast Colorado, and by 6 PM CST, the pressure was down to 990 mb. This low was located along a stationary front that extended east-northeast across Nebraska. A dryline extended south from the low and a cold front was approaching from the west. The area was in the warm sector with the triple point over southwest Nebraska. As the evening progressed, the low and cold front moved into central Nebraska, with the front merging with the dryline. The flow aloft was moderately-amplified with a low over Utah, embedded within a longwave trough over the West, while a ridge was over the eastern United States. In the wake of the earlier showers and storms, within the inflow of the supercell, temperatures were in the middle 70s, with dewpoints in the middle 60s. With mid-level lapse rates 7.5-8.0 C/km, this resulted in MLCAPE around 3000 J/kg. Deep layer shear was around 40 kt. Low-level winds were strong and veered significantly with height, resulting in 0-1 km SRH between 250 and 300 m2/s2. The Supercell Composite Parameter was about 18 and the Significant Tornado Parameter was around 4.