The Southland will see its first major rainfall of the season on Wednesday, raising some fears of slides over denuded burn areas, including in the Cleveland National Forest in Orange County near the site of the recent Holy Fire, forecasters said.

The remnants of Hurricane Rosa — now a tropical depression — will not be much of a factor in the Southland’s impending rain episode, NWS meteorologist Dave Bruno said. Instead, the rain will be largely a product of an upper-level low-pressure system that originated in the central Pacific and was expected to move onshore late Tuesday, according to a National Weather Service forecast.

Although not a monster, the approaching weather system is unusually strong for this time of the year, Bruno said, adding that the lion’s share of the precipitation will crop up Wednesday between noon and midnight.

The approaching system is raising some fears of mud slides and debris flows over areas previously denuded by wildfire — including near the site of the Holy Fire in Orange County and, in L.A. County, the La Tuna Fire near Burbank and the Creek Fire north of Sylmar — but those concerns are not particularly acute because mostly light rain is expected, according to Bruno. However, the risk of slides will increase considerably if thunderstorms appear since they can generate heavy downpours.

A slight chance of thunderstorms was forecast for late Tuesday and Wednesday.

Showers are expected to continue Wednesday evening, followed by a small chance of showers after midnight.

Clearer skies are expected Thursday.

In Orange County, a 30 percent chance of showers will exist after midnight Tuesday, followed by a chance of showers Wednesday morning and a 70 percent chance of it in the afternoon, along with a slight chance of thunderstorms. Showers are likely Wednesday evening, when the chance of measurable precipitation will be 60 percent, along with a slight chance of thunderstorm.

A slight chance of showers will persist in Orange County on Thursday morning before mostly sunny skies prevail in the afternoon, forecasters said.

Wednesday’s highs were expected to be in the upper 60s to mid-70s near downtown Los Angeles, and in the mid-70s in the valleys and inland Orange County.

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