| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2022 | 7.80 | 7.30 | 7.80 | 7.40 | 10.80 | 10.90 | 11.30 | 11.60 | ||||
| 2021 | 1.40 | 1.40 | 1.50 | 2.90 | 3.30 | 3.90 | 3.80 | 4.80 | 4.90 | 6 | 7.10 | 7.50 |
| 2020 | 2.70 | 2.50 | 2.60 | 1.50 | 1 | 1.10 | 1.60 | 0.50 | 1.10 | 1.30 | 0.90 | 1.20 |
| 2019 | 2.50 | 2.50 | 2.40 | 3 | 3 | 2.90 | 2.80 | 2.60 | 2.40 | 2.10 | 2.20 | 2.20 |
| 2018 | 4 | 3.60 | 3.30 | 3.40 | 3.30 | 3.40 | 3.20 | 3.50 | 3.30 | 3.30 | 3.20 | 2.70 |
| 2017 | 2.60 | 3.20 | 3.10 | 3.50 | 3.70 | 3.50 | 3.60 | 3.90 | 3.90 | 4 | 3.90 | 4.10 |
| 2016 | 1.30 | 1.30 | 1.60 | 1.30 | 1.40 | 1.60 | 1.90 | 1.80 | 2 | 2 | 2.20 | 2.50 |
| 2015 | 1.10 | 1 | 0.90 | 0.90 | 1 | 1 | 1 | 1.10 | 0.80 | 0.70 | 1.10 | 1.20 |
| 2014 | 2.80 | 2.70 | 2.50 | 2.50 | 2.40 | 2.60 | 2.50 | 2.40 | 2.30 | 2.30 | 2 | 1.60 |
| 2013 | 3.30 | 3.20 | 3.30 | 2.90 | 3.10 | 3.30 | 3.10 | 3.30 | 3.20 | 2.60 | 2.60 | 2.70 |
| 2012 | 3.90 | 3.70 | 3.60 | 3.50 | 3.10 | 2.80 | 3.20 | 2.90 | 2.60 | 3.20 | 3 | 3.10 |
| 2011 | 5.10 | 5.50 | 5.30 | 5.20 | 5.20 | 5 | 5 | 5.20 | 5.60 | 5.40 | 5.20 | 4.80 |
| 2010 | 3.70 | 3.70 | 4.40 | 5.30 | 5.10 | 5 | 4.80 | 4.70 | 4.60 | 4.50 | 4.70 | 4.80 |
| 2009 | 0.10 | 0 | -0.40 | -1.20 | -1.10 | -1.60 | -1.40 | -1.30 | -1.40 | -0.80 | 0.30 | 2.40 |
| 2008 | 4.10 | 4.10 | 3.80 | 4.20 | 4.30 | 4.60 | 5 | 4.80 | 5 | 4.20 | 3 | 0.90 |
| 2007 | 4.20 | 4.60 | 4.80 | 4.50 | 4.30 | 4.40 | 3.80 | 4.10 | 3.90 | 4.20 | 4.30 | 4 |
| 2006 | 2.40 | 2.40 | 2.40 | 2.60 | 3 | 3.30 | 3.30 | 3.40 | 3.60 | 3.70 | 3.90 | 4.40 |
| 2005 | 3.20 | 3.20 | 3.20 | 3.20 | 2.90 | 2.90 | 2.90 | 2.80 | 2.70 | 2.50 | 2.40 | 2.20 |
| 2004 | 2.60 | 2.50 | 2.60 | 2.50 | 2.80 | 3 | 3 | 3.20 | 3.10 | 3.30 | 3.40 | 3.50 |
| 2003 | 2.90 | 3.20 | 3.10 | 3.10 | 3 | 2.90 | 3.10 | 2.90 | 2.80 | 2.60 | 2.50 | 2.80 |
| 2002 | 1.30 | 1 | 1.30 | 1.50 | 1.10 | 1 | 1.50 | 1.40 | 1.70 | 2.10 | 2.60 | 2.90 |
| 2001 | 2.70 | 2.70 | 2.30 | 1.80 | 2.10 | 1.90 | 1.60 | 2.10 | 1.70 | 1.60 | 0.90 | 0.70 |
| 2000 | 2 | 2.30 | 2.60 | 3 | 3.10 | 3.30 | 3.30 | 3 | 3.30 | 3.10 | 3.20 | 2.90 |
| 1999 | 2.40 | 2.10 | 2.10 | 1.60 | 1.30 | 1.30 | 1.30 | 1.10 | 1.10 | 1.20 | 1.40 | 1.80 |
| 1998 | 3.30 | 3.40 | 3.50 | 4 | 4.20 | 3.70 | 3.50 | 3.30 | 3.20 | 3.10 | 3 | 2.80 |
| 1997 | 2.80 | 2.70 | 2.60 | 2.40 | 2.60 | 2.90 | 3.30 | 3.50 | 3.60 | 3.70 | 3.70 | 3.60 |
| 1996 | 2.90 | 2.70 | 2.70 | 2.40 | 2.20 | 2.10 | 2.20 | 2.10 | 2.10 | 2.70 | 2.70 | 2.50 |
| 1995 | 3.30 | 3.40 | 3.50 | 3.30 | 3.40 | 3.50 | 3.50 | 3.60 | 3.90 | 3.20 | 3.10 | 3.20 |
| 1994 | 2.50 | 2.40 | 2.30 | 2.60 | 2.60 | 2.60 | 2.30 | 2.40 | 2.20 | 2.40 | 2.60 | 2.90 |
| 1993 | 1.70 | 1.80 | 1.90 | 1.30 | 1.30 | 1.20 | 1.40 | 1.70 | 1.80 | 1.40 | 1.40 | 1.90 |
| 1992 | 4.10 | 4.10 | 4 | 4.30 | 4.30 | 3.90 | 3.70 | 3.60 | 3.60 | 3.60 | 3 | 2.60 |
| 1991 | 9 | 8.90 | 8.20 | 6.40 | 5.80 | 5.80 | 5.50 | 4.70 | 4.10 | 3.70 | 4.30 | 4.50 |
| 1990 | 7.70 | 7.50 | 8.10 | 9.40 | 9.70 | 9.80 | 9.80 | 10.60 | 10.90 | 10.90 | 9.70 | 9.30 |
| 1989 | 7.50 | 7.80 | 7.90 | 8 | 8.30 | 8.30 | 8.20 | 7.30 | 7.60 | 7.30 | 7.70 | 7.70 |
| 1988 | 3.30 | 3.30 | 3.50 | 3.90 | 4.20 | 4.60 | 4.80 | 5.70 | 5.90 | 6.40 | 6.40 | 6.80 |
| 1987 | 4 | 3.90 | 4 | 4.20 | 4.20 | 4.20 | 4.40 | 4.40 | 4.20 | 4.50 | 4.10 | 3.70 |
| 1986 | 5.50 | 5.10 | 4.20 | 3 | 2.80 | 2.50 | 2.40 | 2.40 | 3 | 3 | 3.50 | 3.70 |
| 1985 | 5 | 5.40 | 6.10 | 6.90 | 7 | 7 | 6.90 | 6.20 | 5.90 | 5.40 | 5.50 | 5.70 |
| 1984 | 5.10 | 5.10 | 5.20 | 5.20 | 5.10 | 5.10 | 4.50 | 5 | 4.70 | 5 | 4.90 | 4.60 |
| 1983 | 4.90 | 5.30 | 4.60 | 4 | 3.70 | 3.70 | 4.20 | 4.60 | 5.10 | 5 | 4.80 | 5.30 |
| 1982 | 12 | 11 | 10.40 | 9.40 | 9.50 | 9.20 | 8.70 | 8 | 7.30 | 6.80 | 6.30 | 5.40 |
| 1981 | 13 | 12.50 | 12.60 | 12 | 11.70 | 11.30 | 10.90 | 11.50 | 11.40 | 11.70 | 12 | 12 |
| 1980 | 18.40 | 19.10 | 19.80 | 21.80 | 21.90 | 21 | 16.90 | 16.30 | 15.90 | 15.40 | 15.30 | 15.10 |
| 1979 | 9.30 | 9.60 | 9.80 | 10.10 | 10.30 | 11.40 | 15.60 | 15.80 | 16.50 | 17.20 | 17.40 | 17.20 |
| 1978 | 9.90 | 9.50 | 9.10 | 7.90 | 7.70 | 7.40 | 7.80 | 8 | 7.80 | 7.80 | 8.10 | 8.40 |
| 1977 | 16.60 | 16.20 | 16.70 | 17.50 | 17.10 | 17.70 | 17.60 | 16.50 | 15.60 | 14.10 | 13 | 12.10 |
| 1976 | 23.40 | 22.90 | 21.20 | 18.90 | 15.40 | 13.80 | 12.90 | 13.80 | 14.30 | 14.70 | 15 | 15.10 |
| 1975 | 19.90 | 19.90 | 21.20 | 21.70 | 25 | 26.10 | 26.30 | 26.90 | 26.60 | 25.90 | 25.20 | 24.90 |
| 1974 | 12 | 13.30 | 13.50 | 15.20 | 15.90 | 16.60 | 17.20 | 15.90 | 14.90 | 16.30 | 18.40 | 19.20 |
| 1973 | 7.70 | 7.80 | 8.30 | 9.30 | 9.60 | 9.30 | 9.30 | 11.20 | 11.40 | 10.70 | 10.30 | 10.60 |
| 1972 | 8.20 | 8 | 7.50 | 6.30 | 6.10 | 6 | 5.80 | 5.30 | 7 | 7.90 | 7.60 | 7.60 |
| 1971 | 8.50 | 8.60 | 8.80 | 9.40 | 9.80 | 10.40 | 10.10 | 10.20 | 9.90 | 9.20 | 9.20 | 9 |