So Cal/SW AZ, Flash Flood Potential Sep 21-22, 2015

A tropical low pressure system off of the Baja tip is moving northward and will be pumping a lot of moisture up with it. Monday evening and through Tuesday there is expected to be isolated heavy downpours on and off in the AZ and CA southern desert region. These areas are prone to flash flooding, even on the interstates so use caution, especially art night traveling across the area following heavy downpours

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3118