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Warm and dry conditions Thursday across California will give way to distinctly cooler and wet weather heading into the weekend, the National Weather Service said.

Showers, rain, mountain snow and gusty winds were predicted for many areas as a low pressure system moves down from the Pacific Northwest into California on Friday, followed by a second system during the weekend, forecasters said.

A winter storm watch starting in the Sierra Nevada on Friday warns of possible heavy snow above 5,000 feet (1,524 meters) with accumulations of 6 inches to 12 inches (15.2 to 30.48 centimeters), with localized amounts up to 15 inches (38.1 centimeters) .

Significant snowfall was also forecast for Southern California mountains. State highway officials advised motorists that chain controls will be in effect at higher elevations, and there could be delays because of rock falls or debris flows from burn scars.

The forecast of an abrupt change change in the weather follows a long, hot summer and early fall marked by disastrous wildfires feeding on a parched landscape.

About 9,000 fires have scorched more than 4.1 million acres (16,970 square kilometers) in California so far this year. More than 10,400 structures have been destroyed or damaged, and there have been 31 fire-related fatalities.

Several thousand firefighters continue working to complete containment of more than 20 big fires.

The U.S. Drought Monitor reported Thursday that more than 84% of the state — the northern and eastern regions — is now experiencing moderate to extreme drought or abnormal dryness.

Since Jan. 1, San Francisco has had just over 4 inches (10.1 centimeters) of rain, a deficit more than 10 inches to date.

The coastal counties from Monterey south to San Diego remain free of drought indicators, according to the monitor. But there has been little rain.

Since Jan. 1, downtown Los Angeles has had 7.8 inches (19.8 centimeters) of rain, nearly 4 inches (10.1 centimeters) less than normal.

California is expected to be warmer and drier than normal this winter, according to a National Oceanic and Atmospheric Administration outlook released last month.