As Hurricane Harvey’s aftermath dumped rain on the Houston area in August, the staff at the National Weather Service (NWS) knew they were watching history. And as the rain totals were tallied, the agency added not one, but two new colors to its rainfall map: purple for 20 to 30 inches and light pink for over 30 inches. “It’s difficult to predict what has never happened,” says Greg Carbin, who leads the NWS Forecast Operations Branch in College Park, Maryland. “I hope we don’t have to use it again.” The total? Nearly 52 inches in a week in Cedar Bayou, Texas, a record in the continental U.S.