The Weather Prediction Center is warning of a potentially life-threatening and dangerous flood event expected to unfold in parts of central and Southern California today.
The center has issued a rare Level 4 of 4 risk of excessive rainfall for Los Angeles, Santa Barbara and Oxnard, on Sunday. A more widespread Level 3 risk exists for much of coastal California, including San Francisco, where the National Weather Service has also issued its first-ever hurricane force wind warning for the region.
In central and Southern California, widespread rainfall totals of 3 to 6 inches are expected – more than a month’s worth of rain for most. Los Angeles averages just 2.99 inches of rain in February, their wettest month of the year on average. In the mountains and foothills of Southern California, the weather service is forecasting up to a foot of rain.
The National Weather Service in Los Angeles warns the multi-day rain event could be dangerous and life-threatening. It could cause extensive road flooding and significant debris flow over areas that have previously burned in wildfires, possibly causing mudslides in higher terrain. Creeks and streams will rise.
Putting this rare warning into context: It’s hard to emphasize how big of a deal and how rare a Level 4 “high risk” alert is. They are issued on fewer than 4% of days per year on average, but are responsible for more than 80% of all flood-related damage and 39% of all flood-related deaths.
This event is part of an atmospheric river: a moisture plume pumping off the Pacific Ocean, feeding off warmer than average waters.
Dr. Daniel Swain, a climate scientist known for work on Western extremes, notes that heavy rain events like the one unfolding are becoming 10% more intense thanks to more fuel from a warmer climate.