After days of relentless rain, Southern California was awaiting the most intense storm system yet, with evacuations ordered, rescue crews on standby and residents anxiously eyeing already saturated mountainsides denuded by wildfires.
Steady rain began falling late Tuesday and was expected to intensify into early Wednesday.
Bill Patzert, a climatologist at the Jet Propulsion Laboratory in La Cañada Flintridge, told the Los Angeles Times that the weather system bearing down on California was expected to produce dramatic results.
"When you get the very cold air mixing in with the very warm air, it can be quite volatile," he said. Wednesday was "definitely going to be the main event," Patzert told the newspaper.
Forecasters' focus clearly was on Southern California where the monster storm was expected to bring torrential rain, thunderstorms, flooding, hail and possible tornadoes and water spouts. They warned of possible rainfall rates of .75 inch to 1 inch an hour and thunderstorm rates of 2 inches an hour in the region.
"It's going to be a three-ring circus," said National Weather Service spokesman Bill Hoffer. "There's going to be a six-hour time frame in the early morning when it's really going to be dumping on us."
Forecasters expected two to four inches to soak Southern California, including Los Angeles and San Diego, overnight Tuesday and into Wednesday, .
Officials on Tuesday ordered evacuation of 232 homes in La Canada Flintridge and La Crescenta, foothill suburbs of Los Angeles below steep hillsides that burned in 2009 and where mudslides inundated homes and backyards in February.
Walt Kalepsch said his backyard filled up with mud and debris last winter, but he planned to stay the night with his wife and daughter.
"If it gets really terrible, we'll leave. But we've been evacuated so many times, it's like the city's crying wolf," he said. "During the rest of the year, it's absolutely gorgeous. It was just one big wildfire that changed everything."
As the "Pineapple Express" system swept Pacific Ocean moisture across Nevada, Arizona and Utah, Gov. Arnold Schwarzenegger declared a state of emergency in six counties.
The huge and powerful low pressure system off the West Coast pushed precipitation right into the Great Basin.
"It takes a lot of energy to push that moisture over the mountains," said NWS meteorologist Dave Bruno. "This kind of storm could march right across the country and create a lot of bad weather along the way. It could affect the Southern Plains on Thursday and Friday. If it sticks together it'll hit Florida by Saturday."
With rain falling up and down the state, Sierra Nevada ski resorts boasted of record-breaking December snowfall, with the storms bringing a total of 10½ to 15½ feet to Mammoth Mountain.
Rescuers had to pluck some stranded motorists from rain-swollen creeks. Shoppers dodged puddles while buying last-minute Christmas gifts. Disney resorts canceled a plan to shower visitors with artificial snow.
In Orange County, four hikers missing overnight in a flooded canyon in the Cleveland National Forest were rescued Tuesday morning by helicopter after their car was trapped along swollen Trabuco Creek. Rescuers used a bulldozer to retrieve five other people who became stranded by the creek.
Downtown Los Angeles has received more than a third of its annual average rainfall in less than a week.
Parts of the San Gabriel Mountains got more than 18 inches of rain since Friday, with coastal cities like Santa Monica and Long Beach getting more than six inches, the National Weather Service said.
Mudslides are a significant risk for three years after a wildfire and are especially likely anytime the rainfall rate reaches or exceeds one inch per hour, said Susan Cannon, a research geologist with the U.S. Geological Survey.
That's a likely scenario Wednesday in the area burned by last year's Station Fire, which charred 250 square miles above the suburbs tucked below the San Gabriel Mountains.
"It means that once the heaviest rains start, it should be a very active time up there," Cannon said.
For all the perils of the torrential rains, there was a silver lining: The water is expected to help ease the effects of years of drought.
Thursday is expected to be dry, with sunshine. Light rain is forecast for Christmas Day in parts of California.
Water content in the snow pack in California's mountains was at 197 percent of normal and 169 percent of the average measurement for April 1 — traditionally the date when the snow's water content is at its peak, said Ted Thomas, spokesman for the California Department of Water Resources.
As the snow melts, that water will run off into reservoirs that feed the state's extensive agriculture and city water systems.