Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1957 -15.6 -21.1 -30.0 -35.6 -36.1 -33.3 -41.1 -28.9 -30.6 -26.7 -20.6 -12.2 1958 -15.0 -15.0 -28.3 -30.6 -27.2 -41.1 -41.1 -42.2 -40.0 -30.0 -21.7 -17.2 1959 -17.2 -18.3 -25.0 -23.3 -33.3 -32.8 -33.9 -38.9 -35.6 -33.9 -22.8 -14.4 1960 -15.6 -23.9 -31.7 -30.0 -32.8 -30.6 -33.9 -40.6 -33.9 -27.2 -24.4 -14.4 1961 -13.1 -20.0 -29.7 -24.1 -36.2 -34.8 -35.7 -37.2 -33.2 -37.6 -22.3 -16.3 1962 -15.7 -23.9 -28.8 -36.2 -29.3 -40.3 -36.0 -34.7 -43.7 -33.2 -22.0 -15.6 1963 -15.3 -21.3 -31.0 -30.1 -34.0 -28.6 -39.9 -35.2 -36.8 -27.6 -19.4 -17.2 1964 -17.3 -22.6 -25.3 -30.3 -31.1 -31.9 -32.1 -40.4 -35.0 -31.4 -19.8 -13.8 1965 -14.4 -19.5 -28.8 -27.3 -37.0 -34.7 -30.2 -33.1 -39.0 -28.4 -19.1 -13.4 1966 -15.3 -18.6 -25.9 -26.7 -33.6 -29.2 -34.7 -40.3 -34.1 -31.7 -20.1 -13.7 1967 -13.5 -15.6 -26.7 -33.3 -28.0 -32.0 -38.2 -31.4 -38.0 -34.4 -23.2 -14.5 1968 -13.9 -16.8 -24.6 -29.2 -36.5 -41.6 -36.6 -38.7 -42.7 -28.3 -21.6 -15.1 1969 -15.6 -23.6 -24.3 -33.2 -31.1 -38.1 -30.8 -37.3 -33.8 -31.2 -23.5 -14.3 1970 -11.8 -19.0 -21.6 -26.1 -35.0 -30.1 -33.9 -33.8 -35.3 -27.6 -21.4 -14.0 1971 -12.6 -20.7 -26.7 -29.8 -29.4 -35.4 -39.6 -37.4 -34.5 -30.6 -22.7 -14.7 1972 -16.0 -17.8 -24.3 -28.8 -30.3 -30.4 -33.7 -32.8 -33.9 -26.4 -19.8 -14.7 1973 -13.8 -23.7 -29.9 -31.5 -28.2 -32.0 -34.2 -35.0 -33.8 -27.0 -18.2 -14.0 1974 -11.8 -20.3 -25.7 -29.7 -30.6 -32.1 -38.8 -35.2 -40.4 -29.7 -15.9 -12.7 1975 -14.2 -20.0 -27.3 -29.0 -32.2 -32.2 -34.6 -39.7 -35.4 -30.3 -20.2 -14.9 1976 -12.4 -20.4 -24.2 -32.3 -34.8 -35.5 -35.1 -40.5 -40.6 -36.1 -19.5 -13.3 1977 -12.5 -23.2 -26.3 -31.5 -36.0 -33.5 -34.8 -37.1 -39.9 -30.5 -19.4 -14.7 1978 -16.4 -22.1 -23.8 -30.7 -32.6 -34.4 -38.2 -43.8 -37.6 -30.4 -19.5 -14.9 1979 -13.6 -21.8 -27.6 -35.4 -29.6 -32.0 -37.9 -40.9 -32.0 -29.0 -20.6 -12.5 1980 -12.5 -16.0 -24.8 -21.9 -26.0 -35.0 -25.8 -28.9 -34.5 -27.6 -22.4 -14.8 1981 -15.1 -23.1 -23.9 -31.4 -32.1 -30.0 -35.8 -43.0 -35.2 -28.9 -23.1 -14.7 1982 -13.7 -20.0 -29.9 -38.8 -35.8 -30.5 -36.6 -31.8 -36.3 -30.0 -21.7 -13.1 1983 -15.1 -26.5 -27.9 -28.4 -29.5 -39.6 -40.0 -42.5 -34.1 -31.1 -22.9 -15.7 1984 -15.3 -19.5 -21.6 -27.6 -29.7 -28.9 -40.1 -39.2 -36.8 -25.3 -20.2 -12.8 1985 -13.6 -23.0 -27.3 -28.5 -29.4 -30.3 -41.4 -39.1 -33.4 -29.1 -16.3 -15.7 1986 -14.8 -19.8 -27.8 -27.6 -27.0 -36.9 -36.4 -40.6 -44.7 -29.8 -20.8 -14.3 1987 -13.8 -19.1 -32.9 -32.9 -31.3 -28.8 -28.3 -32.1 -34.2 -28.4 -23.5 -14.0 1988 -13.6 -20.7 -29.0 -26.2 -32.0 -34.4 -30.5 -25.9 -28.6 -25.8 -20.1 -12.8 1989 -13.2 -18.8 -24.8 -24.6 -35.8 -38.5 -35.4 -30.6 -35.2 -27.2 -20.2 -13.6 1990 -12.5 -20.1 -32.3 -29.7 -27.6 -38.6 -36.5 -40.3 -30.4 -32.8 -22.5 -13.5 1991 -15.2 -15.8 -29.1 -28.4 -30.1 -32.1 -35.6 -37.6 -31.2 -25.9 -20.4 -11.0 1992 -14.6 -22.5 -22.8 -28.7 -24.0 -32.4 -29.6 -34.1 -33.8 -23.9 -20.7 -12.8 1993 -12.6 -18.1 -27.6 -29.2 -32.1 -29.0 -26.2 -30.6 -34.2 -28.5 -20.6 -13.9 1994 -15.1 -21.9 -29.6 -25.9 -29.9 -31.7 -33.0 -38.9 -36.5 -25.4 -16.9 -11.8 1995 -14.1 -16.8 -29.4 -29.2 -35.7 -26.5 -35.1 -34.6 -32.5 -31.1 -21.4 -13.9 1996 -13.8 -20.8 -26.7 -22.4 -38.0 -30.9 -38.2 -32.0 -34.9 -29.8 -19.2 -12.5 1997 -13.0 -20.1 -26.8 -33.0 -34.0 -28.6 -34.6 -38.8 -33.4 -23.8 -18.2 -10.5 1998 -13.5 -15.6 -27.1 -33.0 -24.0 -25.8 -40.1 -34.6 -35.7 -32.0 -22.5 -14.5 1999 -12.7 -22.1 -26.2 -33.6 -32.8 -34.4 -31.0 -37.8 -28.6 -24.5 -18.6 -14.3 2000 -16.9 -19.1 -21.9 -33.8 -29.3 -30.0 -29.3 -34.1 -30.8 -24.8 -16.7 -15.3 2001 -14.5 -18.0 -22.9 -25.9 -27.8 -28.8 -32.7 -41.4 -33.6 -30.1 -21.4 -15.1 2002 -13.4 -20.2 -19.9 -30.8 -26.8 -30.2 -36.6 -33.9 -24.5 -27.1 -15.9 -14.3 2003 -12.2 -19.9 -22.5 -28.3 -31.5 -33.1 -36.0 -36.3 -33.8 -26.6 -20.7 -13.1 2004 -13.7 -21.0 -28.1 -29.7 -34.2 -32.2 -40.4 -41.5 -37.5 -30.2 -19.4 -14.2 2005 -9.7 -23.0 -28.3 -31.8 -30.3 -30.1 -30.7 -36.6 -26.0 -25.2 -17.9 -12.6 2006 -11.7 -15.3 -28.9 -35.8 -37.2 -31.7 -36.5 -29.6 -33.7 -26.1 -19.2 -14.4 2007 -10.4 -19.7 -22.5 -25.9 -27.0 -29.4 -29.5 -37.0 -32.5 -31.5 -18.3 -14.1 2008 -12.3 -19.8 -23.0 -29.3 -32.0 -30.1 -34.9 -41.2 -27.9 -25.0 -22.4 -15.9 2009 -14.4 -20.9 -24.5 -28.2 -32.9 -34.1 -26.9 -33.5 -35.9 -30.8 -16.8 -12.2 2010 -14.1 -18.5 -22.2 -29.8 -35.7 -35.9 -40.4 -31.4 -33.4 -28.2 -22.5 -14.9 2011 -15.3 -21.8 -26.0 -30.3 -31.6 -33.8 -23.4 -29.2 -38.4 -26.2 -20.1 -14.8 2012 -15.4 -18.9 -24.1 -29.8 -26.7 -37.3 -37.0 -36.4 -33.7 -27.1 -22.0 -11.7