Powerful Storm System to Bring Potentially Heavy Rain to Southern California Thursday and Friday

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A "strong" storm system is forecast to sweep through Southern California on Thursday and Friday, bringing potentially heavy rain to parts of the region and prompting the National Weather Service to warn of possible flash flooding in recent burn areas.

In this file photo, San Dimas Public Works Supervisor Terry Gregory clears a clogged drain last January as heavy rains caused flooding and mud flows in San Dimas, Glendora and Azusa. (Credit: Robert Gauthier / Los Angeles Times)

In this file photo, San Dimas Public Works Supervisor Terry Gregory clears a clogged drain last January as heavy rains caused flooding and mud flows in San Dimas, Glendora and Azusa. (Credit: Robert Gauthier / Los Angeles Times)

Light precipitation is expected to reach the area by Thursday afternoon before developing into moderate to heavy rain in the evening hours, forecasters said.

Periods of moderate to heavy rain could fall in parts of Los Angeles County and surrounding areas from Thursday night into Friday morning, according to the weather service. Scattered showers are likely on Friday after the precipitation tapers off.

Heavier rains near recent burn scar areas could lead to flash flooding in those parts. As a result, as flash flood watch has been issued for those areas and will be in effect between Thursday night and Friday morning, according to the weather service.

Areas under the flood watch include the Santa Monica and San Bernardino mountains, and the San Fernando, Santa Clarita and San Gabriel valleys.

The steady rain could also disrupt the evening commute Thursday evening and rush hour on Friday morning, as possible "ponding of water" forms on freeways in low lying areas, forecasters said. Rain-slickened roads could also be problematic for motorists.

Rainfall totals are expected to be between 1/2 to 1 1/2 inch for the coasts and valleys, with 1 to 3 inches in the foothills and southwest-facing mountain slopes. Heavier amounts are possible in the mountains and foothills.

In addition to rain, snow levels are also expected to plummet to mountain-pass levels by Friday afternoon.  The levels will drop rapidly between 4,000 to 5,000 feet by early evening, falling to as low as 3,500 feet on Friday night.

The 5 Freeway near the Grapevine could be impacted by the snow on Friday night.

Gusty winds are also forecast to hit the area, bringing the potential for tree damage and power outages. The strongest winds are forecast to hit Friday afternoon, according to the weather service.

Deserts and mountains will likely experience wind speeds of 20 to 50 mph, with powerful gusts of up to 75 mph at the mountain ridge tops and 60 mph in desert areas.

Along the coast, winds of 10 to 25 mph are forecasts, with expected gusts topping out at around 30 mph.

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