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| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1962 | 17.5 | 20.6 | 25.7 | 25.9 | 23.8 | 18.7 | 13.4 | 9.6 | 19.4 ] | ||||
| 1963 | 4.0 | 4.8 | 9.3 | 14.7 | 18.8 | 21.8 | 26.0 | 26.7 | 23.0 | 17.7 | 13.8 | 9.9 | 15.9 |
| 1964 | 8.8 | 6.6 | 10.0 | 17.3 | 19.0 | 21.4 | 26.6 | 27.1 | 24.5 | 19.3 | 13.7 | 9.2 | 17.0 |
| 1965 | 6.7 | 7.4 | 8.4 | 12.8 | 17.8 | 20.5 | 25.9 | 26.2 | 21.3 | 17.6 | 15.4 | 8.6 | 15.7 |
| 1966 | 6.9 | 8.9 | 12.1 | 14.5 | 17.9 | 21.0 | 25.4 | 28.2 | 23.2 | 18.4 | 13.1 | 8.1 | 16.5 |
| 1967 | 5.9 | 6.6 | 10.0 | 14.8 | 18.8 | 22.5 | 26.3 | 27.6 | 24.0 | 18.6 | 14.6 | 6.3 | 16.3 |
| 1968 | 6.5 | 4.0 | 9.8 | 14.1 | 17.5 | 20.5 | 24.2 | 26.1 | 23.4 | 18.2 | 13.5 | 11.4 | 15.8 |
| 1969 | 7.9 | 7.9 | 8.9 | 14.5 | 18.2 | 20.3 | 24.7 | 27.2 | 24.5 | 18.0 | 12.6 | 7.8 | 16.0 |
| 1970 | 5.3 | 8.1 | 7.1 | 13.4 | 17.7 | 20.0 | 25.1 | 27.1 | 25.0 | 20.0 | 13.3 | 9.4 | 16.0 |
| 1971 | 6.6 | 7.5 | 9.5 | 14.3 | 17.5 | 21.3 | 26.9 | 26.0 | 23.2 | 17.9 | 14.4 | 9.8 | 16.2 |
| 1972 | 9.6 | 8.2 | 10.6 | 13.9 | 17.9 | 21.3 | 25.7 | 26.1 | 22.3 | 17.9 | 13.8 | 9.3 | 16.4 |
| 1973 | 9.1 | 8.8 | 10.2 | 15.6 | 18.4 | 21.2 | 26.4 | 26.9 | 22.1 | 18.2 | 12.3 | 7.1 | 16.4 |
| 1974 | 6.8 | 6.8 | 9.7 | 14.2 | 18.3 | 20.2 | 24.2 | 26.2 | 22.2 | 18.8 | 13.3 | 9.5 | 15.9 |
| 1975 | 6.7 | 7.0 | 9.9 | 14.4 | 17.4 | 21.1 | 25.9 | 26.7 | 24.8 | 20.0 | 14.5 | 8.8 | 16.4 |
| 1976 | 6.1 | 9.6 | 9.7 | 14.4 | 17.5 | 20.2 | 23.3 | 26.4 | 21.3 | 17.8 | 11.8 | 8.7 | 15.6 |
| 1977 | 4.1 | 5.0 | 11.1 | 15.0 | 17.7 | 21.2 | 26.6 | 25.5 | 23.7 | 19.8 | 14.8 | 10.6 | 16.3 |
| 1978 | 7.6 | 6.7 | 9.7 | 13.9 | 18.2 | 22.3 | 27.1 | 26.9 | 23.8 | 18.4 | 14.3 | 9.7 | 16.6 |
| 1979 | 8.3 | 8.9 | 10.0 | 13.8 | 17.3 | 22.1 | 24.9 | 26.5 | 23.7 | 18.6 | 13.0 | 10.5 | 16.5 |
| 1980 | 7.0 | 5.7 | 10.4 | 13.8 | 17.8 | 22.2 | 25.2 | 24.8 | 22.0 | 18.4 | 13.9 | 7.0 | 15.7 |
| 1981 | 5.0 | 6.6 | 10.3 | 14.4 | 17.5 | 22.0 | 27.2 | 26.6 | 22.8 | 17.9 | 12.7 | 8.7 | 16.0 |
| 1982 | 6.7 | 7.9 | 11.2 | 14.1 | 19.5 | 21.3 | 23.9 | 26.1 | 22.4 | 19.0 | 15.1 | 9.1 | 16.4 |
| 1983 | 7.4 | 6.7 | 10.7 | 15.4 | 18.5 | 21.4 | 25.5 | 26.7 | 24.6 | 19.4 | 12.9 | 8.3 | 16.5 |
| 1984 | 4.8 | 5.0 | 8.3 | 14.7 | 17.6 | 22.3 | 26.3 | 27.2 | 23.2 | 18.5 | 15.5 | 9.2 | 16.1 |
| 1985 | 5.7 | 8.1 | 10.8 | 14.4 | 19.1 | 21.9 | 26.6 | 27.6 | 25.1 | 19.7 | 13.5 | 8.0 | 16.7 |
| 1986 | 5.4 | 5.6 | 9.8 | 14.9 | 18.3 | 22.1 | 25.7 | 26.8 | 23.3 | 17.3 | 13.2 | 10.6 | 16.1 |
| 1987 | 7.7 | 8.4 | 10.4 | 14.2 | 18.2 | 21.5 | 25.5 | 26.5 | 22.7 | 20.2 | 15.2 | 9.6 | 16.7 |
| 1988 | 8.5 | 7.3 | 9.8 | 14.2 | 18.9 | 21.9 | 26.4 | 26.2 | 23.4 | 19.2 | 12.9 | 9.2 | 16.5 |
| 1989 | 10.0 | 9.5 | 10.8 | 15.6 | 18.2 | 20.9 | 25.1 | 26.7 | 24.0 | 18.2 | 14.1 | 9.8 | 16.9 |
| 1990 | 7.3 | 10.8 | 11.7 | 14.4 | 18.4 | 22.8 | 27.2 | 28.1 | 24.8 | 19.1 | 15.5 | 9.4 | 17.5 |
| 1991 | 7.9 | 6.9 | 11.1 | 14.7 | 17.6 | 22.2 | 26.5 | 25.6 | 23.7 | 18.3 | 13.4 | 10.7 | 16.6 |
| 1992 | 8.5 | 7.9 | 11.4 | 15.1 | 18.2 | 20.5 | 25.0 | 26.1 | 24.3 | 18.4 | 13.5 | 10.8 | 16.6 |
| 1993 | 7.8 | 8.5 | 9.9 | 13.8 | 17.9 | 21.8 | 24.3 | 25.2 | 22.3 | 18.2 | 15.3 | 9.4 | 16.2 |
| 1994 | 7.6 | 8.0 | 9.1 | 15.5 | 19.2 | 21.3 | 28.0 | 28.0 | 23.7 | 19.5 | 15.9 | 11.0 | 17.2 |
| 1995 | 7.3 | 7.6 | 10.3 | 13.6 | 17.6 | 20.7 | 25.8 | 27.9 | 23.3 | 19.3 | 12.3 | 8.0 | 16.1 |
| 1996 | 7.3 | 6.6 | 10.1 | 12.3 | 18.4 | 22.9 | 26.1 | 27.3 | 23.5 | 19.2 | 15.0 | 9.6 | 16.5 |
| 1997 | 7.1 | 8.4 | 11.5 | 15.1 | 19.1 | 22.5 | 25.8 | 27.0 | 23.0 | 18.4 | 15.4 | 10.4 | 17.0 |
| 1998 | 7.6 | 10.3 | 10.9 | 17.2 | 20.3 | 22.3 | 26.9 | 28.2 | 25.2 | 20.7 | 14.8 | 10.9 | 17.9 |
| 1999 | 7.8 | 7.7 | 12.0 | 14.7 | 18.1 | 22.0 | 24.1 | 26.5 | 25.4 | 19.9 | 14.2 | 8.9 | 16.8 |
| 2000 | 8.2 | 6.3 | 10.6 | 14.1 | 18.3 | 21.9 | 26.7 | 27.4 | 23.8 | 20.0 | 14.9 | 10.0 | 16.9 |
| 2001 | 7.4 | 8.4 | 10.7 | 14.8 | 18.8 | 22.5 | 26.9 | 27.4 | 23.7 | 20.1 | 13.7 | 9.4 | 17.0 |
| 2002 | 8.7 | 8.6 | 12.2 | 15.7 | 19.2 | 22.5 | 26.0 | 26.4 | 23.7 | 18.3 | 12.1 | 10.3 | 17.0 |
| 2003 | 6.7 | 8.9 | 10.4 | 15.7 | 19.0 | 21.9 | 25.3 | 26.6 | 24.8 | 18.6 | 16.7 | 9.8 | 17.0 |
| 2004 | 6.8 | 8.9 | 10.9 | 15.3 | 19.1 | 23.0 | 27.0 | 27.5 | 24.5 | 19.3 | 14.7 | 11.1 | 17.3 |
| 2005 | 7.0 | 6.9 | 9.3 | 15.2 | 18.5 | 22.9 | 26.7 | 27.2 | 25.3 | 20.2 | 14.7 | 6.9 | 16.7 |
| 2006 | 7.9 | 8.2 | 10.3 | 14.3 | 18.4 | 22.3 | 26.6 | 27.6 | 23.5 | 20.4 | 15.8 | 10.3 | 17.1 |
| 2007 | 8.6 | 10.1 | 11.6 | 14.8 | 19.3 | 22.6 | 25.9 | 28.1 | 26.2 | 20.8 | 14.5 | 10.9 | 17.8 |
| 2008 | 8.6 | 6.8 | 10.9 | 14.9 | 18.5 | 21.6 | 27.5 | 27.3 | 24.6 | 19.9 | 14.5 | 9.6 | 17.1 |
| 2009 | 7.4 | 10.7 | 12.0 | 15.0 | 19.0 | 22.4 | 26.1 | 27.0 ) | 24.0 | 19.7 | 13.9 | 9.5 | 17.2 |
| 2010 | 7.3 | 9.9 | 11.4 | 13.6 | 18.5 | 22.3 | 26.4 | 28.4 | 25.4 | 20.0 | 13.5 | 9.7 | 17.2 |
| 2011 | 4.6 | 9.0 | 8.8 | 14.1 | 18.7 | 22.3 | 26.6 | 27.2 | 24.4 | 19.5 | 16.9 | 9.3 | 16.8 |
| 2012 | 7.4 | 7.0 | 11.0 | 15.2 | 19.5 | 22.0 | 26.6 | 28.1 | 23.5 | 19.5 | 13.3 | 8.4 | 16.8 |
| 2013 | 6.8 | 8.4 | 11.9 | 14.4 ) | 19.4 | 22.8 | 28.2 | 28.8 | 24.6 | 21.4 ] | 13.5 | 8.8 | 17.1 ] |
| 2014 | 7.9 | 8.7 | 11.6 | 14.8 | 18.7 | 21.2 | 25.4 | 26.0 | 23.3 | 19.5 | 14.7 | 7.9 | 16.6 |
| 2015 | 8.3 | 7.8 | 10.7 | 15.4 | 19.0 | 21.0 | 24.7 | 26.1 | 22.8 | 18.6 | 16.2 | 11.2 | 16.8 |
| 2016 | 7.7 | 8.1 | 11.5 | 16.1 | 19.3 | 22.4 | 26.7 | 27.9 | 24.5 | 21.3 | 14.9 | 11.0 | 17.6 |
| 2017 | 8.1 | 8.4 | 10.1 | 16.1 | 19.2 | 21.8 | 27.7 | 27.9 | 23.2 | 20.1 | 13.9 | 8.0 | 17.0 |
| 2018 | 6.3 | 6.3 | 11.9 | 16.4 | 19.5 | 22.2 | 27.2 | 28.4 | 24.3 | 18.6 | 14.6 | 10.7 | 17.2 |
| 2019 | 8.4 | 9.5 | 11.7 | 14.9 | 19.4 | 21.8 | 24.9 | 27.0 | 24.7 | 20.3 | 15.1 | 11.0 | 17.4 |
| 2020 | 10.3 | 10.0 | 12.0 | 13.6 | 19.5 | 23.4 | 24.8 | 28.2 | 23.3 | 19.3 | 15.2 | 9.0 | 17.4 |
| 2021 | 7.7 | 10.1 | 13.6 | 15.9 | 19.1 | 22.6 | 26.9 | 26.8 | 24.6 | 20.3 | 13.8 | 9.7 | 17.6 |
| 2022 | 7.4 | 6.9 | 12.4 | 15.8 | 19.3 | 22.9 | 27.1 | 28.2 | 24.5 ) | 19.2 | 16.2 | 8.5 | 17.4 |
| 2023 | 8.1 | 9.6 | 12.9 | 16.0 | 19.0 | 23.0 | 27.1 | 28.0 | 25.8 | 19.3 | 14.7 | 10.6 | 17.8 |
| 2024 | 9.0 | 10.9 | 11.6 | 16.9 | 18.0 ] | 12.1 ] |
Remarks
The red lines, if any, indicate data inhomogeneity caused by changes in instrumentation, observation methods and/or site location.