7-tornado day a rarity in Virginia according to NWS

Collisions of cold and warm air produced seven tornadoes Monday, including Virginia’s strongest in nearly 15 years.

Tornadoes in April are typical. What happened Monday was not.

“Any time we see an outbreak of three or more tornadoes in one day, I think, from my perspective, it’s unusual,” said Brian Hurley, a National Weather Service meteorologist in Wakefield.

More tornadoes will come, but no one can guess when or where, experts say. By varying estimates, Virginia gets seven to 20 tornadoes a year.

Rick Curry, a Weather Service forecaster, explained the origin of Monday’s tornadoes this way:

A cold front moved east across Virginia. That cold air collided with, and lifted, warm air that already was here.

As that warm air rose, winds in the mid- and upper atmosphere pushed it, causing it to spin — like pushing a ball on one side.

That spinning wind worked its way down to the ground, producing a tornado.

“All those things have to be in the right area at the right time,” Curry said. Not every storm Monday produced a tornado.

Six tornadoes were considered moderate or low-level twisters — 110 mph or less. They were located in Colonial Heights, Brunswick County, Halifax County, Isle of Wight County, Surry County and along the Gloucester County-Mathews County line. The seventh, in Suffolk, appears to have been Virginia’s most powerful tornado since one struck the Petersburg-Colonial Heights area in 1993, killing four. The 1993 tornado produced winds up to 225 mph.

Evidence indicates the Suffolk tornado produced winds up to about 160 mph, the Weather Service said. No one was killed.

Modern tornado records began in Virginia 58 years ago, said Jerry Stenger, research coordinator for the University of Virginia’s climatology office. Since then, tornadoes have killed 28 people in the state — roughly one every two years.

“Fortunately, the vast majority of tornadoes that we see are very weak,” he said.

The record for Virginia tornadoes in a year was 87 in 2004, most of them lower-strength twisters, experts say.

The tornado-creating conditions that Curry described are typical for this time of year, Stenger said. In summer, Virginia’s tornadoes more often are spun off from localized thunderstorms or dying tropical storms.

The remnants of Hurricane Ivan spawned 40 tornadoes Sept. 7, 2004, Virginia’s one-day record, state statistics show.

July is Virginia’s most active month for tornadoes.

More tornadoes will come, but no one can guess when or where, experts say.

Staff writer Bill Geroux contributed to this report.