A powerful winter storm was bearing down Wednesday on California and forecasters warned of heavy snowfall in the northern mountains while predictions of widespread rainfall elsewhere raised concern about flash flooding near wildfire burn scars.

Santa Barbara County issued a recommended evacuation warning for south coast communities including Montecito, where a storm dropped an enormous amount of rain In the early morning hours of Jan. 9.

Flash floods carrying huge boulders blasted through Montecito, destroying or damaging hundreds of homes. Twenty-one people were killed and two remain missing.

The county is following a rigorous new system of alerts that emphasizes evacuations well in advance of storms rather than suggesting residents can use their discretion.

Officials hoped to decide Thursday whether to issue a mandatory evacuation order before the system intensifies in the southern half of the state early Friday.

People cannot be forced to leave their homes under a mandatory evacuation order, but authorities said they should not be expected to be rescued while the storm is occurring.

"Our intention is to make sure that you have a plan, that you are prepared, and that you are safe," said Sheriff Bill Brown. "Just because the skies are blue right now doesn't mean there isn't a threat."

People with mobility issues or those with large animals should get out now, officials said. There were no estimates on how many people may have left the area.

Montecito and neighboring communities on the coastal foothills of the Santa Ynez Mountains lie below slopes burned bare by the largest wildfire in recorded California history as well as other fires in recent years.

Evacuation fatigue for some residents is a factor. Some evacuated multiple times during the wildfires, and then again when the mudslides hit.

Geologists estimate that the scorched earth won't grow vegetation for three to five years, meaning every time a major storm moves into the area, residents may be asked or ordered to evacuate.

"It's kind of our way of life until the land grows back," Grimmesey said.

The latest storm was expected to begin in the far northern portion of the state Wednesday afternoon then ramp up on Thursday, when a blizzard warning goes into effect in much of the Sierra Nevada.

The National Weather Service said northern mountains were expected to receive 3 feet (0.9 meter) to 5 feet (1.5 meters) of snow, and up to 7 feet (2.1 meters) in localized areas.

The dump would be a boon to the Sierra snowpack, which is vital to the state's water supply but is only about a quarter its normal size for this time of winter.

Forecasters, however, focused on a host of hazards for anyone trying to drive through the mountains.

"Travel is highly discouraged," the Sacramento weather office said flatly.

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Associated Press writer Christopher Weber contributed to this report.