The outlook is cloudy with a chance of butterflies

Rob Crilly
Radar captured a vast cloud of butterflies - National Weather Service Boulder

The colourful specks swirled one way and then another, mystifying weather forecasters as they pored over radar images trying to decode the patterns.

But, after some detective work, they finally figured out that pictures showed not a weather front moving through the Denver area but a 70-mile cloud of butterflies.

Paul Schlatter, of the National Weather Service, said he first thought it might be migrating birds.

But the wave was moving north-west with the wind at a time when birds are heading south for the winter.

He appealed to social media users for help in identifying the phenomenon.

He had his answer when members of the public said they had seen Painted Lady butterflies floating in the wind.

Unusually large numbers had descended on Colorado’s Front Range in response to plentiful flowers.

The species is found across the continental US and they migrate to the south-western US and north-western Mexico in the autumn.

 

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