Flood watch declared for Orange County ahead of significant rainfall

It may not be a white Christmas in Southern California, but it’ll definitely be a wet one, according to a flood warning issued by the National Weather Service Wednesday morning.

Rain is expected to begin late Thursday evening — the heaviest of it occurring after Thursday midnight — and continue through Friday morning with light showers expected through noon.

The storm is the result of an atmospheric river in the Gulf of Alaska, which meteorologist Casey Oswant explained is a type of rain-producing weather system that typically draws moisture from the tropics.

“Because this is an atmospheric river, we’re going to tend to get more rainfall just because the air mass is warmer and warmer air can hold more moisture,” Oswant said. “In some of the colder winter storms that we’ve gotten where we’re not pulling up any tropical moisture and it comes from the north like Canada or the Gulf of Alaska, we tend to get just less rainfall overall.”

Rain is expected to fall at around 1½ to 2 inches in Orange County, but closer to 2½ to 3 inches near the Santa Ana Mountains — not an insignificant amount for Southern California.

“If you look at the East Coast, Midwest or even the Pacific Northwest, they might just shrug it off,” Oswant said.

“But for us, it is a decent amount of rain and it’s all going to fall in a confined period of about less than 24 hours or so. It’s a lot of rain in a relatively short chunk of time. We just want people to prepare and to know there is a potential for flooding, especially in the burn scars of Orange County — the Bond burn scar [in Santiago Canyon] particularly.”

“We want people to make sure they’re on alert and prepared to evacuate if county officials deem it necessary,” Oswant said.

The flood watch is in effect across coastal and inland Orange County, but also includes San Bernardino, Riverside, San Diego counties and the Inland Empire and those living near the burn scars of the Bond, Apple and El Dorado fires. Officials say flash flooding is possible.

Residents are encouraged to monitor weather forecasts and be alert for potential flood warnings and those in flood-prone areas should be prepared to take action in the event of a flood.

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