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Graphical Climatology of Downtown San Francisco: Daily Temperatures and Rainfall, by Year (1921 – Present)
By Charles Fisk*, Newbury Park, CA.
Latest update: 21 Feb 2013
Note: Website is in process of redesign. No updates except Precip. until completed.
The following is a graphical climatology of Downtown San Francisco, California temperatures and precipitation, from 1921 through 2012. Included are summary overview charts followed by 92 year-to-year graphs depicting daily temperatures, temperature anomalies, and precipitation. The 1921 to 2012 period of record includes observations from four different Downtown locations.
Data for 1921-2009 were accessed from the NOAA National Climatic Data Center (NCDC) on-line site http://lwf.ncdc.noaa.gov/oa/climate/climatedata.html . Data utilized to construct some of the Climogram products were accessed from the International Station Meteorological Climate Summary Version 4.0 (1996). Current year’s data can be accessed from the NWS-Monterey website at http://www.wrh.noaa.gov/mtr/ and the above NCDC online link.
CLIMATE OVERVIEW GRAPHS
SAN FRANCISCO MEAN AND RECORD DAILY MAX/MIN TEMPERATURES BY MONTH new
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR
SAN FRANCISCO RAINFALL
DOWNTOWN SAN FRANCISCO SEASON-TO-DATE 2012-13 RAINFALL **
DOWNTOWN SAN FRANCISCO AVERAGE MONTHLY RAINFALL
DOWNTOWN SAN FRANCISCO WATER YEAR RAINFALL (1849-50 THRU 2011-12 SEASONS)
CLIMOGRAMS FOR SAN FRANCISCO INT’L AIRPORT:
OTHER SUMMARY CLIMATE GRAPHS:
DOWNTOWN SAN FRANCISCO ANNUAL MEAN TEMPERATURES, BY YEAR (1871-2012) **
DOWNTOWN SAN FRANCISCO AVERAGE DAILY TEMPERATURE RANGES, BY CALENDAR DAY
YEAR-TO-YEAR GRAPHS – INTERPRETATION
The uppermost chart for a given year’s page (accessed by the links below) are “floating-bars” of the year’s daily maxima and minima temperatures. Superimposed on the bars are two line traces, the upper one connecting 1921 to present mean daily maxima, the lower one mean daily minima. The bars depict the varying diurnal, synoptic, long-wave, seasonal, and sea-surface temperature anomaly influences on San Francisco temperature over time, and subjectively, some years’ features can be quite interesting to look at.
The second chart down shows the day-to-day mean temperature anomalies (daily mean temperature less the corresponding long-term climatological mean). Vertical lines extending upward from the zero line indicate above average means for the day (colored red), those extending downward indicate below average daily means (colored blue). In general, the most extreme departures for Downtown San Francisco are positive, reflecting to a large extent the occurrence of warming offshore flow episodes. In the entire 1921-present series, greatest positive departure for any given calendar day is +25 F for 14 June 2000, the most negative departure -22 F for 11 December 1932.
YEAR-TO-YEAR GRAPHS – COMPLETE SET OF LINKS
1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
The third chart down shows the second chart’s anomalies in deseasonalized (“standardized”) form. This adjusts for the fact that individual calendar days have higher or lower inherent year-to-year variability in mean temperature. For example, Downtown San Francisco calendar day mean temperature standard deviations for the 1921-2009 period ranged from 5.77 F (24 June) to 2.86 F (1 December). To create a common relative anomaly scale for each day, the anomalies are divided by their corresponding calendar day standard deviations to generate “standardized departures” or “z-scores”. Those scores of plus or minus 3.0 occur just 1.9% of the time; nearly all of these (96%) positively signed, reflecting extreme warming offshore flow events. Greatest positive standardized departure in the record is +5.7 for 17 July 1988, greatest negative –4.9 for 11 December 1932.
The bottom chart depicts daily precipitation totals, as high as 5.54 inches (5 November 1994).
LINKS TO YEARLY GRAPHS OF PARTICULAR INTEREST, WITH ACCOMPANYING NOTES
1925 – Wettest May in all history (4.02”).
1926 – As influenced by a strong El Nino, warmest March, April, and May since the start of the official history (in 1871). Also warmest year to date.
1931 – Steady above normal warmth over first half of year. Second warmest year to date
1932 – Sharp December cold snap over the 8th-14th. Coldest week long period (38.9 F) of 1921-present era. Max/min temperature only 35/27 F on 11th. Daily min (27 F) on 11th coldest such temperature recorded in Downtown San Francisco history.
1934 – Warmest year up this time (58.9 F) until tied by 1983.
1937 – Coldest January in all history. First 52 days of the year each below average in mean temperature. .
1938 – Nineteen consecutive measurable rain-days over late January to mid-February.
1939 – Warmest September on record up to this time. September 17th-23rd the warmest week long period (79.3 F) in all history down to present.
1940 – Lowest average day-to-day variability in maximum temperature (3.3 F) of any year in history.
1940-41 – Strong El Nino episode. Wettest July-June water year (35.05”) since 1889-90.
1941 – Lowest average daily temperature range (10.6 F) of 1921-present period.
1949 – Very cool January and February help produce coldest winter in all history (Dec. ’48 – Feb ’49).
1951– Coolest Summer (Jun.-Aug.) since 1911 and coolest Summer through the present.
1955 – Coolest year (55.2 F) since 1901 and through the present.
1957-58 – Strong El Nino. Wettest July-June water year (36.48”) since 1889-90.
1958 – Scattered four to six week much above normal temperature spells over the year. Heavy rains during late Winter/early Spring. March and April with 13.69” rain, wettest March-April since1884. Mildest December in all history.
1962 – Coolest July since 1901 and coolest September since 1910 and through the present. Second wettest October (5.51”) in history. Rainstorms interrupt 1962 World Series.
1964 – Coolest Spring (March-May) since 1911.
1967 – Irregular anomaly pattern in temperature and rainfall over course of year. Coldest April in all history, wettest June (1.42”) since 1884.
1969 – Second lowest annual maximum temperature (82 F) in history. Lowest 78 F in 1878.
1970 – Highly irregular temperature anomaly pattern over course of the year – Mix of short and long-term warm/cold spells.
1971 – In an otherwise cool year, warmest day in Downtown San Francisco history (101 F/ 72 F) on14 September.
1972 – Severe cold snap in early December. Coldest December since 1908.
1975-76 – Driest rain year (July-June) in all history (7.16”).
1976-77 – A second droughty rain year in a row. Fourth driest in history (10.02”). Two-year rain deficit about 25”.
1982-83 –Great El Nino. Water year precipitation (38.17”) most since 1889-90.
1983 – Annual mean temperature ties 1934 for warmest in history up to this time. Eight of the next fifteen years including 1983, equal to or warmer than 1934 (temperature history). Wettest March (9.04”) and warmest Summer up to this time.
1984 –Highest average day-to-day variability in maximum temperature (5.0 F) of any year in history. September warmest calendar month in all history (69.4 F).
1985 – Summer mean temperature eclipses 1983 record.
1986 – Warmest January and February in all history, third warmest March. Warmest year to date by 1.2 F
1988 – 103 F on 17 July; highest temperature ever recorded in Downtown San Francisco.
1989 – Five-day summer-like spell in early April. All days 87 F or higher.
1990 – Intense cold spell in late December, but 1990 still as warm in the mean as 1934 and 1983. Highest average daily temperature range (15.7 F) of 1921-present period.
1992 – Warmest year in all history (60.8 F). Also warmest Spring and Fall
1993 –Warmest Summer in all history.
1994 – Coldest and 2nd wettest November (11.49”) in all history.
1995 – Warmest July in all history.
1996 – Second warmest year in all history (60.3 F).
1997 – Third warmest year in all history (60.1 F).
1997-98 – The other great El Nino of the 20th century. Wettest rain year (47.22”) since 1861-62, second wettest in all history. Wettest February (14.89”) in history.
1999 – La Nina year. Coolest year since 1975 and coolest Spring since 1911.
2000 – 103 F on 14 June, ties July 1988 mark for highest temperature ever recorded in Downtown San Francisco.
2003 – Scattered abbreviated much above normal temperature spells.
2004 – Another year of abbreviated much above normal temperature spells.
2005 – Annual maximum temperature (82 F) ties 1969’s mark for second lowest since 1878.
2006 – Coldest March since 1911 and 4th wettest March (8.74”) in all history . Unusual heat in July.
* Member, American Meteorological Society