More than 41 million Americans across California, Nevada and Arizona are under flood watches on Wednesday amid a rare, high risk for excessive rainfall and flooding.

A slow-moving storm is expected to dump another inch or more of rain on an already saturated Southern California on Friday. The heaviest rain is forecast during the morning hours as the first of two systems moves slowly over the region,

The National Weather Service extended a Flash Flood Warning for parts of Los Angeles and Ventura counties, effective until 6 p.m. Wednesday.

The Valley will see a lull in the wind and rain through midday but one more round of strong winds will move through around dinner time.

Over a month's worth of rain is expected in a few days across parts of Southern California, forecasters warned.