Unstable weather in Southern California raise flooding, debris slide concerns

LOS ANGELES - Tropical Storm Kay has moved on, but the atmospheric instability it created was still lingering Monday, bringing the threat of more rainfall in the mountains and other areas, raising concerns about localized flooding and debris slides.

A flood watch will be in effect until 10 p.m. in the Los Angeles County mountains and the Antelope Valley, including Lancaster, Acton, Mount Wilson and Palmdale, according to the National Weather Service.

The NWS also issued a series of flood advisories Monday afternoon as storm systems developed over the area, particularly in the eastern reaches of the county such as Big Pines and Llano, and in the Bobcat Fire burn area in the eastern San Gabriel Mountains.

Forecasters said any storms that develop could produce "heavy downpours with rainfall rates exceeding one inch per hour."

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Record rainfall was reported in Palmdale and Sandberg on Sunday. Palmdale Airport recorded 0.46 inches of rain, breaking a record for the date of 0.23 inches set in 1976. Sandberg recorded 0.32 inches of rain, breaking a record of 0.31 inches set in 1976.

NWS forecasters warned that excessive runoff could result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Mud and debris flows are possible around recent burn areas.

Downpours on Sunday night led to mudslides in the Lake Hughes area that inundated dozens of vehicles and trapped as many as 50 people who had to be rescued by county fire crews. Some roads in the area were still blocked on Monday afternoon.

"Thunderstorm activity is expectedly quite heavy across the mountains and Antelope Valley today (Monday) with ample moisture and instability lingering after Kay's departure," according to the NWS. "Storms are also very slow moving so any storms that do develop tend to stay put for quite some time increasing the threat of flooding. Storms may not be confined to the mountains as there is some instability at lower elevations."

Forecasters said the unstable weather will continue through the evening.

Conditions were expected to return to normal by Tuesday.

"This pattern will give way to a cooler and more typical marine layer pattern starting Tuesday and continuing into the weekend," according to the NWS. "Temperatures will drop to below normal levels for Wednesday and Thursday, with a small warm up possible thereafter."