Northern and Central California
Mid-Winter Dry Spells
 Jan Null, CCM
 updated March 4, 2022
On almost as regular a 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 72 rainfall seasons (i.e., July 1 to June 30), since 1950, there has been a "dry" period in December or January averaging 21 days. For practical purposes a "dry period" here is defined as consecutive dry days with no rain, or consecutive days broken by non-consecutive days of very light (* i.e., ≤ 0.08 inches) rain]. 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.

The shortest dry spell was 8 days in 1994-95, an El Niņo event!  The longest dry spell was 57 days in 2013-2014, which ended with 12.54 inches, during an ENSO-neutral year. Of the 10 longest (i.e., ≥ 32 days), six were "neutral years; and eight of the 10 ended the rainfall season below normal.

Even the very wet El Niņo seasons of 1982-83 and 1997-98 had intervening dry spells and 24 and 18 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.

Longest Consecutive San Francisco Mid-Winter Dry (i.e., days ≤ 0.08") Periods
Rank Season Dry Days Began Ended Season Total ENSO Type
1 2013-2014 57 12/7/2013 2/1/2014 12.54  
2 2021-2022 54 1/8/2022 3/2/2022   Moderate La Niņa
3 1952-1953 49 1/21/1953 3/9/1953 21.10 Weak El Niņo
4 2014-2015 48 12/20/2014 2/5/2015 18.19 Weak El Niņo
5 1960-1961 43 12/11/1960 1/22/1961 13.87  
6 1962-1963 42 12/18/1962 1/28/1963 22.15  
7 1966-1967 41 12/10/1966 1/19/1967 29.41  
8 2019-2020 38 1/29/2020 3/6/2020 11.70  
9 1956-1957 37 12/6/1956 1/11/1957 15.04  
10 1970-1971 32 1/17/1971 2/17/1971 18.79 Moderate La Niņa
11 1999-2000 32 12/10/1999 1/10/2000 24.89 Strong La Niņa
12 2017-2018 32 1/25/2018 2/25/2018 17.53 Weak La Niņa
13 1987-1988 28 1/30/1988 2/26/1988 17.74 Strong El Niņo
14 1953-1954 27 12/7/1953 1/2/1954 14.27 Weak El Niņo
15 1971-1972 26 12/27/1971 1/21/1972 11.06 Weak La Niņa
16 1976-1977 26 1/13/1977 2/7/1977 11.08 Weak El Niņo
17 1979-1980 26 1/18/1980 2/12/1980 24.57 Weak El Niņo
18 1961-1962 25 12/18/1961 1/11/1962 17.65  
19 1975-1976 25 1/10/1976 2/3/1976 8.05 Strong La Niņa
20 1998-1999 25 12/21/1998 1/14/1999 23.49 Strong La Niņa
21 1982-1983 24 12/23/1982 1/15/1983 38.17 Very Strong El Niņo
22 2000-2001 24 12/15/2000 1/7/2001 19.47 Weak La Niņa
23 1963-1964 23 12/21/1963 1/12/1964 12.32 Moderate El Niņo
24 1974-1975 23 12/4/1974 12/26/1974 18.33 Weak La Niņa
25 1990-1991 23 1/10/1991 2/1/1991 14.08  
26 1955-1956 22 1/28/1955 2/18/1956 27.17 Moderate La Niņa
27 1967-1968 22 12/19/1967 1/9/1968 14.46  
28 1985-1986 21 12/8/1985 12/28/1985 28.68  
29 1996-1997 21 1/27/1997 2/16/1997 22.63  
30 1954-1955 20 12/10/1954 12/29/1954 15.74 Weak La Niņa
31 1984-1985 20 1/8/1985 1/27/1985 20.01 Weak La Niņa
32 1991-1992 20 1/8/1992 1/27/1992 19.20 Strong El Niņo
33 1993-1994 20 12/15/1993 1/3/1994 15.22  
34 2002-2003 20 1/23/2003 2/11/2003 23.87 Moderate El Niņo
35 1997-1998 18 12/15/1997 1/1/1998 47.22 Very Strong El Niņo
36 2001-2002 18 1/3/2002 1/20/2002 25.03  
37 2008-2009 18 1/3/2009 1/20/2009 18.11 Weak La Niņa
38 2004-2005 17 12/9/2004 12/25/2004 31.87 Weak El Niņo
39 2020-2021 17 1/5/2021 1/21/2021 8.97 Moderate La Niņa
40 1964-1965 16 12/2/1964 12/17/1964 22.29 Weak La Niņa
41 1972-1973 16 12/23/1972 1/7/1973 34.36 Strong El Niņo
42 1977-1978 16 1/20/1978 2/4/1978 27.86 Weak El Niņo
43 1980-1981 16 12/5/1980 12/20/1980 14.63  
44 1995-1996 16 12/30/1995 1/14/1996 24.89 Moderate La Niņa
45 2010-2011 16 1/14/2011 1/29/2011 28.87 Strong La Niņa
46 2012-2013 16 1/7/2013 1/22/2013 16.61  
47 1981-1982 15 1/29/1982 2/12/1982 36.63  
48 1983-1984 15 12/31/1983 1/14/1984 22.47 Weak La Niņa
49 1986-1987 15 1/7/1987 1/21/1987 13.86 Moderate El Niņo
50 2005-2006 15 12/2/2005 12/16/2005 34.42 Weak La Niņa
51 1973-1974 14 1/17/1974 1/30/1974 27.96 Strong La Niņa
52 1992-1993 14 1/22/1993 2/4/1993 26.66  
53 2003-2004 14 1/10/2004 1/23/2004 20.54  
54 1950-1951 13 12/20/1950 1/1/1951 24.00  
55 1951-1952 13 12/5/1951 12/17/1951 32.56 Moderate El Niņo
56 1959-1960 13 12/25/1959 1/6/1960 15.47  
57 1968-1969 13 12/29/1968 1/10/1969 25.09 Moderate El Niņo
58 1969-1970 13 12/26/1969 1/7/1970 20.80 Weak El Niņo
59 1978-1979 13 1/31/1979 2/12/1979 18.70  
60 1989-1990 13 1/17/1990 1/29/1990 14.32  
61 2009-2010 13 12/30/2009 1/11/2010 24.09 Moderate El Niņo
62 2011-2012 13 1/24/2012 2/5/2012 15.64 Moderate La Niņa
63 1965-1966 12 12/12/1965 12/23/1965 16.33 Strong El Niņo
64 1988-1989 12 1/11/1989 1/22/1989 17.43 Strong La Niņa
65 1958-1959 11 1/13/1959 1/23/1959 10.46 Weak El Niņo
66 2006-2007 11 1/5/2007 1/15/2007 16.89 Weak El Niņo
67 2018-2019 11 12/25/2018 1/4/2019 25.72 Weak El Niņo
68 1957-1958 10 12/22/1957 12/31/1957 36.48 Strong El Niņo
69 2007-2008 10 1/11/2008 1/20/2008 17.35 Strong La Niņa
70 2015-2016 10 12/25/2015 1/3/2016 23.26 Very Strong El Niņo
71 2016-2017 9 1/24/2017 2/1/2017 32.34 Weak La Niņa
72 1994-1995 8 1/31/1995 2/7/1995 34.02 Moderate El Niņo

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