This has been an unusually mild year in Tornado Alley, which is good news, of course, for the people who live here, but a little frustrating to scientists who planned to chase twisters as part of a $10 million research project.

“You’re out there to do the experiment and you’re geared up every day and ready. And when there isn’t anything happening, that is frustrating,” said Don Burgess, a scientist at the University of Oklahoma. But he was quick to add that he is pleased the relative quiet has meant fewer injuries and less damage.

Nationwide, there were 826 tornadoes this year through June 30, compared with an average of 934 for the same period during the previous three years, according to the National Severe Storms Laboratory in Norman, Okla. Most twisters strike in Tornado Alley, which generally extends from Texas and Oklahoma to Kansas, Nebraska, Iowa and Minnesota.

During a remarkable 17-day lull from mid-May through early June, there were no tornado watches issued anywhere in the United States. And that is typically the height of the season in Tornado Alley.

“It was very, very unusual,” said Joe Schaefer, director of the Storm Prediction Center in Norman, which, like the Severe Storms lab, operates under the National Weather Service.

Meteorologists are attributing the relative calm not to anything dire, like global warming, but to the shifts in the jet stream that happen from time to time. When the jet stream runs south to north in the spring over the central states, there are usually plenty of tornadoes. When it’s more west to east, as it is this year, tornadoes are less common.

The serenity has proved exasperating for people like Burgess and other researchers working on Vortex2, a project funded by the National Science Foundation and the National Oceanic and Atmospheric Administration to study tornadoes in May and June.