Jim Kalina, a meteorologist for the National Weather Service, said the service received 10 separate reports of tornadoes in eastern Colorado on Thursday afternoon.

Kalina said that survey parties from the weather service will go into the field Friday to determine exactly how many tornadoes there were and how strong they were.

He said that some of the 10 sightings may have been the same tornado. Kalina emphasized that at this point, the weather service has not determined the strength of the tornadoes.

©The National Weather Service
The National Weather Service's Doppler radar caught an image of the Weld County tornado at 11:44 a.m. on May 22, 2008.

He called the outbreak "somewhat unusual."

Typically, around Memorial Day is when the most tornadoes in Colorado occur, he said. But what was unusual here, he said, was the violence of Thursday's outbreak.

"We don't usually see them destroying a couple of towns and a tornado that is three-quarters of a mile wide," said Kalina. "That is unusual for here."