Rain storm coming to Southern California: flooding, debris flows possible

 Flash flood water blackened by ash and debris from the Holy Fire rushes along Trabuco Creek  in Orange County, California on Thursday, November 29, 2018.  (Photo by Mark Rightmire, Orange County Register/SCNG)

Flash flood water blackened by ash and debris from the Holy Fire rushes along Trabuco Creek in Orange County, California on Thursday, November 29, 2018. (Photo by Mark Rightmire, Orange County Register/SCNG)

A slow-moving storm will drench parts of southern California scarred by a wildfire last summer. Periods of rain, some heavy, are expected to fall from tonight through Thursday across the San Diego metro area as a low pressure system pumps abundant moisture from the Pacific Ocean into the region. The rain will help alleviate the drought which started there months ago, but it could also prove to be too much wet weather at one time, causing floods and debris flows.

Alex Tardy, a meteorologist at the National Weather Service-San Diego office, tells FreighWaves that parts of the city could get flooded if the San Diego River rises far enough above its banks. The river flows just north of downtown San Diego, parallel to I-8, emptying into Mission Bay near SeaWorld. By the time it’s all over, the city could receive almost a month’s worth of rain during the storm’s two day span. The forecast is for one to one and a half inches, while an average December sees around one and three quarters inches, according to NWS records. Other nearby coastal communities from Miramar northward to Oceanside could end up with some flooded streets and homes, too. Drivers should be ready for possible road closures on I-5, I-8, I-805, and state routes 52, 67, 94, 125, and 163.  Check updated road closures on this web site.

Heavy rain will also hit the area where the Holy Fire burned during the summer. The fire was first reported on August 6 in Holy Jim Canyon (from which the fire gets its name), a community of about 40 homes and cabins in the Santa Ana Mountains north of San Diego. The fire jumped the crest of the mountains into neighboring Riverside County and eventually spread across more than 23,000 acres before it was fully contained on September 13.

The fire damaged about 18 buildings and structures and injured three firefighters, but no deaths were reported. Forrest Clark Gordon was arrested for allegedly starting the fire intentionally. The results of a third psychiatric evaluation are pending before he goes back to court.

Tardy says the approaching storm could drop two to three inches of rain on parts of the Santa Ana Mountains which have peaks ranging from five to 10 thousand feet above sea level, covering about 2,100 square miles. What this means for the people in Lake Elsinore, Temescal Valley, and Rancho Santa Margarita in Trabuco Canyon is that mud and more debris left over from the Holy Fire could flow down the mountains into their towns. This would not likely lead to evacuations or long-term disruptions in the supply chain, but it could lead to temporary road and school closures which took place after heavy rain in these areas last week. For truckers, it means they might run into roadblocks on I-15 and SR-241 through these areas.

Check the latest weather alerts on this interactive map to keep track of any Flood Watches and Flood Warnings that may be issued for southern California.

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