Downtown Los Angeles may get half of the 3.6 inches of rain it received in all of 2013 from the upcoming storm systems, according to AccuWeather officials.
The two storm systems are expected to move into Southern California starting Wednesday and will last through the start of the weekend.
The rainfall would bring little relief amid a state of emergency drought that was issued by Gov. Jerry Brown more than a month ago. Los Angeles County officials are asking residents and businesses to shut irrigation systems off.
"We all need to do our part to help conserve water, so the very best and most effective thing anyone of us can do to take immediate advantage of the coming rain is to simply shut our sprinkler systems off," said Supervisor Don Knabe. "Your yard won't need to be watered until later next week, at the very least."
Meteorologists say the second storm, scheduled to arrive Friday, will bring the most rain and they expect about 2 to 4 inches, perhaps more in some areas of Southern California.
Both systems combined will produce the heaviest rainfall seen since March 2011.
Weather officials say snow will materialize in areas at and above 5,000 feet. Some resorts could see about 1 to 2 feet of fresh snow.
"It's been almost three years since we've had rain like this," said Bill Patzert, a climatologist for the Jet Propulsion Laboratory in La Cañada-Flintridge. "This is not a February or March miracle, but any rain is sweet, because everything is so dry."
While the rain is badly needed, it would take several seasons of above-normal rainfall to bust the drought gripping California.
Eleven of the last 15 years have seen below-normal rainfall, making dry weather the norm over an extraordinarily long period, he said. Even if L.A. got a strong 2 inches of rain, the city would still be only about 30% to 40% of normal for this time of year.
Stuart Seto, a weather specialist for the National Weather Service in Oxnard, said the storm expected to hits the region Friday could linger through Monday. He said the heaviest rain should fall Friday morning through the afternoon.
In the meantime, firefighters, public works and law enforcement officials are girding for the inevitable problems that good, hearty rains cause after a long, parched spell, especially in the recent burn areas.