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
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 19211922192319241925192619271928192919301931193219331934193519361937193819391940194119421943194419451946194719481949195019511952195319541955195619571958195919601961196219631964196519661967196819691970197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012
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
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.
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