Weather forecasters sometimes warn of storms that unleash such unusual rain they are described as 100-year or even 500-year floods. Here’s what to know about how scientists determine how extreme ...

“Most 100-year-olds probably can’t get up out of bed for 20 minutes,” added Aramis Pettinato, 25, of Staten Island, “and she’s doing a show for an hour and a half, singing and hitting ...

A 500-year flood means such an event has a 1 in 500 chance, or 0.2%, of occurring in a year. Another concept scientists use is how frequently an event of a certain intensity is expected.