May 18, 2011 6:48 PM by Greg Boyce
DENVER (AP) - Officials say marble-sized hail has been falling northwest of Denver. The National Weather Service said the hail was 2 to 3 inches deep on the ground in Thornton Wednesday and no bigger than three-quarters of an inch in diameter. But it was so widespread that plows were used to clear the roads in the north suburbs.
The thunderstorm also spawned a tornado warning, which expired without any reports of touchdowns in the Denver area. The warning covered parts of Adams and Broomfield counties. TV viewers provided photos showing funnel clouds starting to form but hovering far above the ground.
Authorities say a cold front Wednesday morning brought in cooler air combined with moisture, helping create funnel action in the atmosphere.