DENVER—Northern Colorado’s mostly agricultural Weld County is known as a prolific tornado spawning ground—but its twisters are usually small, short-lived and in the county’s sparsely populated eastern plains.
Thursday’s deadly tornado was different, targeting a 35-mile-long string of farm towns from Platteville to Windsor and beyond as it moved through the western part of the county.
Normally, Weld County’s tornadoes “lightly touch down in the wide, open spaces,” said state Rep. Jim Reisberg, D-Greeley, who watched the large storm develop near his home. “This is the first big one I’ve seen.”
While destructive tornadoes are generally known to roar through the Midwest, Weld County had the highest number of reported tornadoes of any county in the United States in the 50 years between 1950 and 2000, with 213 twisters reported, according to the National Weather Service.
About seven tornadoes are typically reported in the county each year.
“Weld County does have a history of being a high-frequency tornado climate,” said Nolan Doesken, a state climatologist and a researcher at Colorado State University.
Doesken said a typical Weld County tornado starts south of U.S 34, south of Greeley and Windsor, and moves east toward open ground. It doesn’t last long and might show up only as a funnel in the clouds or swirls of dust on the ground.
Doesken called the area the “Denver cyclone convergence zone.” Southeasterly winds bring moisture that forms the eastward-moving storms.
The western part of Weld County is the least tornado-prone portion, Doesken said. That’s where Thursday’s tornado touched down, and its path was unusual, moving southeast to northwest. The storm system eventually moved into Wyoming.
“Often the cloud base is high, but in this case the cloud base was very low,” Doesken said.
Doesken relied on friends and family for descriptions of conditions surrounding Thursday’s tornado. He was at the University of Georgia Thursday, where he was speaking about the Community Collaborative Rain, Hail and Snow Network, a volunteer network of weather observers run out of the Colorado Climate Center at Colorado State University.
