From the National Weather Service in Oxnard

Flash flooding possible on Tuesday in and around the recent burn areas of Los Angeles and Ventura counties; Strong and moist southerly flow associated with a storm system just off the coast will bring moderate to heavy rainfall to the area for most of Tuesday. Rainfall of this intensity and duration has the potential to bring dangerous flash flooding with damaging mud and debris flows to the recent burn areas.

A flash flood watch means that conditions may develop that lead to flash flooding. Flash flooding is a very dangerous situation. Flash flooding and debris flows will be a particular threat in and below the recently burned areas. Southern California residents in or below the recently burned areas are urged to take the steps necessary to protect their property. Persons in the watch area should remain alert and follow directions of emergency preparedness officials.

Significant rain expected for much of southwestern California from tuesday into Wednesday: A strong upper level low pressure system over the eastern pacific ocean will continue to develop tonight, then slowly approach the west coast through Tuesday. This storm has the potential to bring a period of heavy rainfall to much of southwest California Tuesday into Tuesday evening. There is a chance that rain could develop across much of the region as soon as late tonight. Strengthening south to southwesterly flow aloft ahead of this storm will tap into a rich subtropical moisture source well off the coast of Mexico, increasing the potential for heavy rainfall.

The potential exists for 1 to 2 inches of rain in coastal and valley areas, with 2 to 5 inches in the foothills and mountains. The one main concern remains the amount of low level easterly flow that could develop on Tuesday morning which could help to diminish some of the rainfall amounts. However, it appears that rain will become more widespread and heavier as the day progresses on Tuesday and possibly linger across Los Angeles County on Tuesday evening.

There remains a potential of a 2 to 3 hour burst of heavy rainfall with this system on Tuesday, where rainfall rates around one half inch per hour will be possible. Rainfall rates of this intensity could bring the threat of flash flooding and mud and debris flows to locations in and around recent burn areas. A flash flood watch has been issued for the recent burn areas from Tuesday morning through Tuesday evening. Additional rock and mudslides will also be possible in non-burn areas...especially along highway 1 and canyon roads in the Santa Monica mountains.

Other potential impacts from this storm system include gusty southeast to south winds Tuesday, especially across higher terrain where gusts over 50 mph will be possible. The subtropical nature of this moisture will likely keep snow levels very high, generally above 7500 feet through at least Tuesday night. Scattered showers behind the main front will likely linger into Wednesday or Wednesday night and snow levels would lower some at that time. Residents across the southland, especially those who live near the recent burn areas, such as the Colby and Springs burn areas should monitor the latest National Weather Service forecasts and statements about this potentially significant storm system. Listen to NOAA weather radio or your favorite local media outlet for the latest updates on this storm system.