The blizzard that struck northwest Nebraska and the tornadoes that hit northeast Nebraska were part of the same deadly weather system, according to the National Weather Service.
Three family members from Lincoln died on snow-slickened roads in northwest Nebraska. On the eastern side of Nebraska, one person was seriously injured near Wayne and about a dozen others sustained less serious injuries from the tornadoes.
Becky Kern, meteorologist with the weather service in Valley, Neb., said a huge low pressure system moving out of the Rockies ushered in the storms. Warm, humid conditions ahead of the system set the stage for the tornadoes, both on Thursday and Friday, she said.
The tornadoes on Friday in Wayne and Macy were worse than the one on Thursday in Lancaster County because the system was closer, she said.
The storm dumped one to four feet of snow in the area where Nebraska, South Dakota and Wyoming come together, according to AccuWeather Inc. The World-Herald's private weather consultant.
AccuWeather meteorologist Brett Anderson says the intense storms, coupled with wild weather elsewhere in the U.S., were linked to a patten in the jet stream that leads to stalled, atypical weather systems. The jet stream is a river of fast-moving air in the upper atmosphere that serves as a route for storms to ride along, at the same time that it functions as a barrier between conflicting masses of air.
Rather than traveling along a fairly straight west-to-east route, the jet stream last week more closely resembled a rollercoaster, with steep dips south into North America, followed by equally steep climbs northward. This type of path means that storms take longer to move through, he said.
As the storm moved out the Rockies, cold air from the west clashed with the unusually warm, humid air from the east, Anderson said. This, too, contributed to the tornadic weather.
Tornadoes and blizzards are not uncommon in October, but storm systems like the one that swept through last week are rare.
The last time Nebraska had a tornado during October was in 2001, according to University of Nebraska-Lincoln applied climatologist, Ken Dewey, who detailed tornado statistics on the blog, SNR Climate Corner.
Dewey said October tornadoes account for only about 3 percent of the state's twisters, on average.
The last time Nebraska had an EF-4 in October was in 1956, according to the National Weather Service.
For South Dakota, the blizzard was a “megastorm” that earned a place in the record books, according to the Rapid City office of the National Weather Service.
Rapid City received 23.1 inches of snow. Most of that, 19.0 inches, came on one day: Friday. That single day brought more snow than the city has had during the entire month of October, based on records dating to 1888, according to the weather service. The previous monthly record for October was 15.1 inches set in 1919.
For more information: National Weather Service details on Wayne tornado.