These swathes of water vapor from the tropics can be hundreds of miles wide and thousands of miles long, and bring with them enormous quantities of water; the one that arrived in early January dropped more than 30 inches of rain statewide. In Montecito, which had just been ravaged by December’s Thomas Fire, half an inch of rain fell in a matter of minutes and caused deadly flooding and mudslides.
In the Bay Area, atmospheric rivers already cause more than half of the major floods, and more than 70 percent of those in the North Bay. But predicting when and where flood waters will rise is difficult. While the National Weather Service has radars that track storms regionally, the current system was designed with Midwest thunderstorms in mind and often misses the rain that falls in the coastal hills of northern California. To upgrade flood prediction in the Bay Area, a team of water agencies and weather researchers is installing a new radar system that is customized to the region. “It will tell us how much, when, and where it will rain with greater precision,” says Carl Morrison, executive director of the Bay Area Flood Protection Agencies Association. The project is funded by a $19.8 million grant from the state Department of Water Resources; the first of five regional radars has been installed in San Jose. RM