The worst of Southern California’s first major rainstorms of the season is expected to hit Sunday morning. Here’s what you need to know:
timing
Forecasters from the Meteorological Service have issued flood warnings for the highest risk hours, from 10am Sunday to 4pm Monday.
Weather service meteorologist Ryan Kittle said Sunday night will be a time of particularly high concern.
This is “a slow-moving storm, so it’s going to be stubborn. It’s here to stay,” said Alex Tardy, a meteorologist with the National Weather Service’s San Diego office. “Monday is going to bring waves of moisture. So I think that’s going to really bring a lot of rain and snow.
forecast
The mountains of Los Angeles and Ventura counties could see 2 to 3 inches of rain, while elsewhere anywhere from half an inch to 1 inch of rain could fall.
Thousand Oaks and Oxnard could see up to three-fifths of an inch of rain by Monday; Redondo Beach, Santa Clarita and Fillmore, 7/10 inches; and Long Beach, four-fifths of an inch. inches; and downtown Los Angeles, more than an inch.
If the storm produces more rainfall than the upper limit, Ontario’s coastal areas of Orange, Riverside, Lake Elsinore, Temecula and San Diego counties could see 1 to 1.5 inches of rain. . Rainfall amounts of 0.7 to 1 inch are possible in San Diego and 1.5 to 2 inches in San Bernardino.
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Flooding issues in burn areas
Flood warnings are issued when weather conditions are favorable for flooding. “This does not mean flooding will occur, but it is possible,” the weather service said.
Forecasters have increased their forecasts for rainfall. The adjusted forecast is the result of a low-pressure system moving down from Canada that appears to be a little further west — farther from the Southern California coast — than originally expected — which will make the storm wetter.
Kittel said this has led to “increasing concerns about mudslides on some of the burn scars.”
Still, considerable uncertainty remains Saturday afternoon, with the outcome depending on the storm’s precise track and speed, said Kristan Lund, a meteorologist with the National Weather Service in Oxnard.
If a low-pressure system moves westward toward the water, it will absorb more moisture, leading to higher rainfall totals, while an inland route to the east means less rainfall, she said. If the storm ends up moving a little slower than expected, she said, it could roll over an area and extend the duration of rain in that area, or lead to increased rainfall across the board.
“These patterns tend to be harder to predict because you really don’t know what it’s going to end up doing until it arrives,” she said.
Forecasters say there is now a 10 to 20 percent chance of severe flash flooding and mudslides capable of damaging roads and homes in the most vulnerable areas that have recently burned, namely Pacific Palisades and the Palisade around Malibu and Franklin Fire areas, the Eaton Fire around Altadena and Pasadena, the Hughes Fire around Castaic Lake and the Bridge Fire in the Angeles National Forest north of Glendora.
Prepare
Advice from the weather service includes avoiding recently burned areas during this period. Use sandbags to protect property. Residents who decide to stay can “stock up on supplies in case the roads are blocked.”
context
The rainfall is expected to break record or near-record drought conditions in Southern California. Much of the region received less than 5 percent of the average cumulative rainfall for this period in the water year, which began on October 1.
Since October 1, downtown Los Angeles has received just 0.16 inches of rain, just 2 percent of the average rainfall for this time of the water year (6.48 inches). The average annual rainfall in downtown Los Angeles is 14.25 inches.
Southern California is now in either an “extreme drought” or a “severe drought,” according to the U.S. Drought Monitor.
