The New Orleans area saw more rain than typically falls in all of April over a few hours on Monday

The New Orleans area saw more rain than typically falls in all of April over a few hours on Monday, causing dangerous flooding. There's just a 1-2% chance of this kind of rainfall happening in any given year, according to NOAA data, but unlike many storms in New Orleans, Monday's was not a result of tropical storms. CNN's Derek Van Dam brings you the latest