A string of storms that marched across California this month provided enough rain to boost reservoir levels and slightly improve drought conditions after three consecutive dry years.
The state still likely needs several consecutive wet winters, but the latest U.S. Drought Monitor report offers reason for "cautious" optimism with several months left in California's wet season. This month's storms brought precipitation to most of California, pushing the Sacramento River to its highest level since Dec. 31, 2005.
Consecutive days of rain and snow led to a decrease in the percentage of the state under the Monitor's most severe drought category, called exceptional drought (D4). Last week, 55 percent of California was in the exceptional drought category. The latest report shows 32 percent of state in the D4 category.
Nearly 95 percent of the state remains under severe drought, according to the Monitor.
California's critically low water reservoirs remain well below historical average for mid-December, but Drought Monitor researchers noted "good capacity increases" of 6 to 10 percentage points in northern and central California's major reservoirs.
"It takes years to get into a drought of this severity, and it will likely take many more big storms, and years, to crawl out of it," said Jay Famiglietti, a researcher at the Jet Propulsion Laboratory.
A study of satellite data released by NASA's Jet Propulsion Laboratory earlier this week found that at the peak of the drought earlier this year, water storage in the Sacramento and San Joaquin river basins was 11 trillion gallons below normal seasonal levels.
"With several more months still left in the wet season, it is possible that additional storms similar to the ones that just occurred will continue to chip away at the long-term hydrological drought, and the addition of lower temperatures would help build the snow pack," according to the report.
Rainfall has been trending above normal in many places so far during the 2014-2015 rain season that began July 1. As of Wednesday, downtown Los Angeles had collected 4.47 inches, more than 1.4 inches more than normal to date. A year earlier, it had collected just 0.86 inch to date. Downtown San Francisco had tallied 13.40 inches, or nearly 6.5 inches more than normal to date.
But drought improvement will depend largely on this season's precipitation in the Sierra Nevada Mountain range. Springtime runoff from the melting Sierra Nevada mountain range snowpack supplies water for an estimated 25 million Californians. In November, the southern Sierra had received just 47 percent of its normal rain and snow so far, and the northern Sierra 79 percent.
The report noted that temperatures remained above normal, so more rain than snow was reported at higher elevations.
The tropical Pacfic Ocean phenomenon known as El Nino also could have a say in California's drought situation. The chance of El Nino weather conditions, which can potentially usher moisture into California, developing this winter for the Northern Hemisphere increased to 65 percent in December.
That figure represents an increase from last month's estimate of 58 percent.
Gov. Jerry Brown in January declared a drought emergency, and asked Californians to cut residential water use by 20 percent -- a mark that has not been met, according to recent estimates. Farmers in the Central Valley have fallowed fields and mandatory water restrictions are in effect as California faces a fourth-consecutive dry year.