Did Colorado just see its largest hailstone on record?

A storm chaser reported a 4.5 inch diameter hail stone on Sunday evening near Otis, and that would tie the largest hailstone ever recorded in the state of Colorado, according to the Colorado Climate Center,.

There’s a catch: The 4.5 inch-sized hail report was not documented with a photo, making it difficult to verify as having tied a state record, according to the National Weather Service (NWS) office in Boulder.

“Someone that told us that there were (4.5 inch hailstones), but there’s nothing there to verify it. It’s word of mouth,” said Frank Cooper, a meteorologist with NWS Boulder. “There’s no measuring device. It’s just (the storm chaser’s) hand. It’s hard to verify if it was four-and-a-half inches or not, unless we have a measurement of it right next to it.”

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A storm chaser near Otis — in northern Washington County — reported the 4.5 inch (grapefruit-size) hailstone to NWS Boulder on Sunday evening as a line of powerful storms moved through northeast Colorado. That led to an official report of 4.5 inch hail that NWS Boulder passed along to the Storm Prediction Center (SPC), the official governing body for severe weather.

But the lack of visual proof, according to the Colorado Climate Center and its list of rules for verifying a record, will make it a challenge to add to the lengthy list of 4.5 inch hailstones in Colorado. There are 20 documented instances of 4.5 inch hail in Colorado, the most recent of which fell in Adams County in 2011.

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“Always carry a ruler so we can break the record next time it happens,” said meteorologist Becky Bolinger, Colorado’s assistant state climatologist.

Meteorologist Chris Spears of CBS Denver first spotted the possible record on Monday.

The largest worldwide hailstone ever recorded was eight inches and nearly two pounds, falling in Vivian, South Dakota in July 2010. Colorado and the Plains are prone to seeing large hail due to a unique combination of high elevation and an overall susceptibility to severe weather.