Northern California
Mid-Winter Dry Spells
Jan Null, CCM
updated February 2018
On almost as regular basis as the swallows returning to San Juan Capistrano an extended period of dry weather likes to return to Northern and Central California in the middle of winter.

Based on San Francisco's daily rainfall, over the past 67 rainfall seasons (i.e., July 1 to June 30) there has been a "dry" period in December or January averaging 20 days. For practical purposes a "dry period" is defined here 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.

The bottom line is that an extended period of dry weather is the rule and not the exception in the middle of almost every winter as the atmosphere settles into a two to three week period of equilibrium dominated by high pressure.

Season Consecutive        *Dry Days Begin Date *Intervening Days/Amount
1950-51 13 17-Dec  
1951-52 12 6-Dec 1/.08
1952-53 13 21-Jan  
1953-54 13 21-Dec 1/.01
1954-55 16 14-Dec  
1955-56 20 28-Jan  
1956-57 33 6-Dec 2/.03
1957-58 8 6-Dec  
1958-59 12 12-Jan  
1959-60 13 15-Dec  
1960-61 36 19-Dec 1/.02
1961-62 21 22-Dec  
1962-63 42 18-Dec  
1963-64 19 25-Dec 2/.08
1964-65 19 6-Feb  
1965-66 21 7-Jan 1/.02
1966-67 30 11-Dec 1/.01
1967-68 23 19-Jan  
1968-69 13 24-Dec  
1969-70 12 26-Dec  
1970-71 29 17-Jan  
1971-72 21 30-Dec  
1972-73 15 24-Dec  
1973-74 11 20-Jan  
1974-75 22 5-Dec 2/.04
1975-76 25 10-Jan  
1976-77 26 13-Jan  
1977-78 16 20-Jan 1/.02
1978-79 15 19-Dec  
1979-80 26 18-Jan  
1980-81 16 5-Dec  
1981-82 12 6-Jan  
1982-83 22 24-Dec  
1983-84 15 31-Dec  
1984-85 11 27-Dec  
1985-86 21 8-Dec  
1986-87 15 7-Jan  
1987-88 28 30-Jan  
1988-89 11 11-Jan  
1989-90 36 26-Nov  
1990-91 17 20-Dec  
1991-92 17 8-Jan 1/.04
1992-93 14 22-Jan  
1993-94 20 15-Dec 1/.03
1994-95 8 31-Jan  
1995-96 15 31-Dec 1/.02
1996-97 20 27-Jan 2/.07
1997-98 17 15-Dec 2/.03
1998-99 21 21-Dec 2/.02
1999-00 27 14-Dec 1/.03
2000-01 22 16-Dec 1/.03
2001-02 18 3-Jan 1/.02
2002-03 19 24-Jan  
2003-04 11 10-Dec 1/.04
2004-05 17 9-Dec  
2005-06 14 3-Dec 1/.03
2006-07 12 5-Jan  
2007-08 10 11-Jan  
2008-09 18 3-Jan  
2009-10 12 31-Dec 1/.05
2010-11 14 31-Dec  
2011-12 49 1-Dec  
2012-13 16 7-Jan 1/.01
2013-14 36 12-Dec 2/.08
2014-15 56 21-Dec 1/.07
2015-16 9 25-Dec 2/.06
2016-17 10 23-Dec  

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