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SAN FRANCISCO – Much-needed rain fell on downtown San Francisco and elsewhere in California on Wednesday at the outset of what the parched state hopes is the start to a one-two punch of stormy weather.
The storm was expected to move down the coast, dumping a half-inch to an inch of rain in southern areas late in the day, forecasters said.
A potentially stronger storm moving in late Thursday could bring thunder and dump up to 2 inches of rain in central and southern valleys, 2 to 4 inches in the foothills and up to 6 inches in some mountain spots.
State water officials plan Thursday to survey the anemic mountain snow pack, and will likely find that California's precipitation is badly lagging what's needed to quench the region's thirst.
After 2013 ended as the state's driest year on record, all that predicted rain and snow should be nothing but good news. But there also was a risky side of the downpours.
If the rainfall rate is intense, it could bring flash flooding, "and our ground is so dry ... that we'll probably get more runoff than we're absorbing," said Bonnie Bartling, a National Weather Service weather specialist in Oxnard.
About 25 miles northeast of Los Angeles, the suburbs of Glendora and Azusa were taking precautions well in advance of Friday's predicted heavy rains because they sit at the foot of the steep San Gabriel Mountains where a wildfire last month burned nearly 2,000 acres.
Glendora on Wednesday raised its flooding protocol alert level for a second time, urging that residents near the burn area voluntarily evacuate or prepare essentials such as medications and important papers in case a mandatory evacuation order is given.
Glendora provided thousands of sandbags to residents who streamed into a city yard to fill the bags and drive them away.
Sandbags were also being provided in other foothill communities along mountain ranges east and west of Los Angeles, where other fires have burned in recent years.
The National Weather Service said light-to-moderate rain from the first storm was expected through midday Thursday in Southern California, and that as of late Wednesday morning light rain and sprinkles had fallen only as far south as the border of Ventura and Los Angeles counties, well north of Glendora-Azusa burn area.
The weather service said the second storm will be stronger and move across Southern California from late Thursday through late Saturday, reaching Los Angeles County early Friday morning with rainfall amounts ranging from 3-6 inches in the foothills, and up to 8 inches in localized areas.
"Residents located near burn areas should be alert for the potential of mud and debris flows Friday through Saturday," forecasters said.
The National Weather Service also noted the potential for mud and debris flows from the burn area of the May 2013 Springs Fire, which scorched nearly 38 square miles of the Santa Monica Mountains as it burned from the edges of suburban homes down to the beach about 50 miles west of downtown Los Angeles.
Numerous other wildfires statewide left scarred landscapes over the past year, including a 400-square-mile area devastated by last summer's forest fire in and adjacent to Yosemite National Park in the Sierra Nevada.
A so-called Pineapple Express storm brought rain and snow to California earlier this month, and when it departed, the Sierra Nevada snowpack had grown but was still only 29 percent of normal.
"The big difference between the storm earlier in the month in California and the coming two storms is in the area it will affect," Ken Clark, an Accuweather meteorologist, said in an email. "Much of the rain that occurred with the storms early in the month was in the northern half of the state with only very small amounts getting down into the Los Angeles and San Diego area."
The second of the two storms will bring by far the heaviest of rain to Southern California, he wrote. "In fact as much, or more rain, may fall in parts of Southern California than fall, let's say, around the (San Francisco) Bay Area when all is said and done."
Downtown San Francisco is close to its February average of 3.86 inches of rain to date, but it is 11.62 inches below normal for the rain year that began on July 1.
Downtown Los Angeles has recorded only 0.23 inch of rain this month, 3.05 inches below normal to date. The location has received only 1.23 inches since July 1, a deficit of 9.52 inches.