Southern California is bracing for the first significant rainstorm to hit the region in nearly a year, beginning Monday and with the heaviest rain expected in some burn areas, forecasters said.
Almost four inches of rain is expected in eastern Santa Barbara County and western Ventura County over 12 hours from Monday evening through Tuesday morning, forecasters said. The Thomas fire, which was centered in these two counties, burned more than 281,000 acres in that area last month, making it the largest fire on record in California.
"Unfortunately it's centered almost exactly where the Thomas fire was," said Kathy Hoxsie, a meteorologist with the National Weather Service.
The mountains above the San Gabriel Valley are "kind of a secondary hot spot," Hoxsie said. From 2 1/4 to 3 inches of rain is expected there.
"If we drew a map of where we would least like to have the heaviest rain, we would draw it where the Thomas fire was and maybe where the Sand fire was last year and the La Tuna this year -- that looks to be where we've got a couple of bull's-eyes," Hoxsie said.
When a fire sweeps through an area, it not only burns the vegetation, but also affects the soil, Hoxsie said.
"When you have these burn scars with that kind of crystallized soil, it doesn't soak in the way it should; it runs off," Hoxsie said. "With that kind of heavy rain, if we're talking 4 inches in 12 hours, that will cause some problems anywhere. But the biggest concern is those debris flows, because if we get that high amount of rainfall -- it's a double-headed issue. You can get flash flooding periods, and in addition to that you can get the debris flows."
Thunderstorms in the region are most likely Tuesday.
"The problem with thunderstorms is that they can produce a lot of rain intensely in a small area," Hoxsie said. "That would be another threat to these burn areas."
The lowest-level snow is expected to reach is about 4,000 feet on Tuesday morning, which could affect the Grapevine, Hoxsie said.
"If we get snow down to 4,000 feet, we're going to have problems with transportation getting through on (Interstate) 5 and certainly any of the other areas around where the passes get up close to 4,000 feet," Hoxsie said.
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