Predicting tornado activity for the season is not an easy task. “We don’t have a good feel” for how things will develop this year, said meteorologist John Stoppkotte with the National Weather Service in North Platte.
However, don’t use the recent past as an indication, he said: With the lack of low-level moisture, “the number of tornadoes we’ve had over the last couple of years have been few and far between.”
Nebraska has a 30-year average of 49 tornadoes per year, but there were only 26 statewide in 2022.
“We have seen a shift of the weather pattern as of late,” but it is unclear how things will develop, Stoppkotte said. There is “no clear signal” during years that coincide with ending of a La Niña pattern and going toward a neutral pattern such as we have now.”
The La Niña climate pattern, characterized by cool surface waters in the tropical Pacific Ocean, appears to be weakening, which may moderate precipitation patterns in the central part of the U.S.
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Typically, “ingredients for severe weather include ... good low level moisture for storm growth ... some amount of lift in the atmosphere ... and some amount of shear,” Stoppkotte said.
Lift can be created by a front or dryline. A front is a transition zone between air masses of different densities and usually different temperatures. A dryline is a boundary separating moist and dry air masses.
Shear is when the wind changes speed or direction as the air rises, typically in the lowest 3.5 to 5 miles of the atmosphere.
“These elements tend to come together over parts of the Plains and southern states when an active jet stream exists; similar to what we’ve been seeing over the last few weeks,” Stoppkotte said.
During these conditions, instability in the atmosphere can cause rapid cloud formation and growth, along with severe weather.
Some areas of Nebraska are more prone to tornadoes than others.
Lincoln County had 104 confirmed tornadoes during the 72 year period from 1950 through 2021, or 1.4 per year. That does not include all the funnel cloud sightings. Tornado density in Lincoln County for the period was 40.6 per 1,000 square miles.
Hall County, where Grand Island is located, had a tornado density of 136 per 1,000 square miles, the most of any county in the state. The runner-up was Hamilton, the next county to the east, with a density of 120.
If Nebraska has a “tornado alley,” it would be the area in south central Nebraska that includes Kearney, Grand Island, Aurora and Osceola. Going back south, it would take in York and Geneva and continue to the Kansas line. Hebron and Nelson would be part of Nebraska’s tornado alley. The boundary would then extend northwest to include the area around Clay Center, Hastings and Kearney.
North central Nebraska and the northern and central Panhandle had a low tornado density of 13 to 39 per 1,000 square miles. Southwest Nebraska, including Broken Bow, North Platte, Ogallala and Imperial was in the 25 to 40 range. Scotts Bluff County had a tornado density of 83 and the southern Panhandle ranged from 54 to 58.
Garden County, where Oshkosh is located, had the lowest tornado density, at 12 per 1,000 square miles, for the 72 year period. The county level data is available at lincolnweather.unl.edu/nebraska-tornadoes-county-data.
Tornadoes are rare during winter and occur most frequently from April through July. However, March 23, 1913, Easter Sunday, was the worst day for destructive tornadoes in Nebraska’s recorded history, according to NWS data at weather.gov/oax/topten-tornados.
Although tornadoes can occur anytime day or night, two-thirds hit between the hours of 3 and 8 p.m.
The seven very destructive tornadoes that developed on Easter in 1913 hit southeast Nebraska from 5 to 7 p.m.
Four were rated F4, were 400 to 800 yards wide, and traveled more than a combined 155 miles. They caused heavy destruction and killed at least 159 people.
Tornadoes are rated according to their top three-second wind gusts, from EF-0 (65 to 85 miles to per hour) to EF-5 (over 200 mph).
However, “Nobody knows the ‘true’ wind speeds at ground level in most tornadoes,” and “The amount of wind needed to do similar-looking damage can vary greatly, even from block to block or building to building,” according to the NWS website. “Even experienced damage-survey meteorologists and wind engineers can and often do disagree among themselves on a tornado’s strength.”