The drought update reflects the lack of rain and snow in January.
The December 2014 storms have had a positive effect in some areas of California, but a dry January have expanded the drought in other regions.
The report released Thursday shows that the December storms have benefitted west-central California, reducing the level of severe drought (D2 on the graphic) in Marin, Sonoma, San Francisco, and northernmost San Mateo Counties.
But for the Sacramento Valley and the Sierra Nevada, the worst level of drought ("exceptional") expanded.
"Following a month of subnormal precipitation, exceptional drought (D4 on graphic) has been brought back into part of the Sacramento Valley from Sacramento, Yolo, and western El Dorado Counties northward through Butte County," the report stated. "Reservoirs near and north of this region are still above their levels at the start of the current wet season, but water-year-to-date totals have dropped back to near average and 24-month precipitation totals are among the lowest 2 to 10 percent of historical occurrences."
The exceptional drought also expanded "along and east of the central and southern Sierra Nevada, eastward past the ridge line to include the eastern slopes of the range from Inyo County, California northward through Douglas County, Nevada."
The report said the Sierra Nevada snowpack is "well short of the historic mid-January average in the central and southern parts of the range due to subnormal winter precipitation combined with abnormal warmth."
"Since October 1, 2014, precipitation totals are 3 inches to locally over a foot below normal from the slopes of eastern Fresno and adjacent Inyo Counties northward through eastern Nevada County," the drought summary stated.
The forecast thorough January 18 includes rain for parts of northwest California, but lesser amounts (0.5 - 1 inch) for the San Francisco Bay Area and Sacramento Valley.
And next week is expected to be warm and dry.
The drought monitor said "subnormal precipitation is anticipated throughout the West Coast states and most of Nevada from January 19-23."
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