Cue "It's Not Unusual" (by Tom Jones), because an extended period of dry weather in the middle of winter isn't unusual for northern and central California. And given, the current medium range models the next chance of significant rain may be another week and a half off.
Based on San Francisco's daily rainfall, over the past 69 rainfall seasons (i.e., July 1 to June 30) there has been a "dry" period in December or January averaging 19 days. For practical purposes a "dry period" here is defined as consecutive dry days with no rain, or consecutive days broken by no more than two non-consecutive intervening days of very light (* i.e., ≤ 0.08 inches) rain].
The shortest dry spell was 8 days which occurred twice, in 1957-58 and again in 1994-95. Both of these seasons were during El Niño events! The longest dry spell was 56 days in 2014-2015, when there was 18.19 inches. All of these dry periods began in December or January with the exception of the 1964-65 period which was 19 days but did not begin until February 6th.
Even the very wet El Niño seasons of 1982-83 and 1997-98 had intervening dry spells and 22 and 17 days respectively.
