NP Index is the area-weighted sea level pressure over the region 30N-65N, 160E-140W.
Monthly NP values (-1000 mb) Jan 1899 - March 1999
J F M A M J J A S O N D
1899 9.9 9.3 9.8 14.8 14.6 16.8 17.8 18.0 13.9 14.5 2.7 7.4
1900 6.6 6.3 5.1 13.1 12.5 12.5 15.9 16.5 14.9 13.8 12.1 4.3
1901 8.9 12.1 12.5 21.2 16.5 14.5 16.5 16.7 13.5 11.8 10.3 9.1
1902 6.0 5.1 16.9 15.1 15.5 13.9 16.8 15.8 15.3 13.1 12.1 15.6
1903 10.2 11.6 18.0 19.1 15.0 12.9 18.3 16.4 15.8 14.1 10.6 9.2
1904 11.9 16.9 17.0 15.7 14.7 17.4 16.7 19.0 16.2 14.5 9.5 9.6
1905 8.9 5.8 8.6 11.1 16.1 16.7 17.9 15.4 15.7 15.1 9.1 7.6
1906 13.7 8.5 12.5 13.0 16.0 14.0 17.3 13.1 14.6 10.6 11.8 14.4
1907 14.6 10.3 19.5 15.7 14.2 15.1 17.1 17.8 16.9 14.0 12.3 7.1
1908 8.6 11.7 19.4 15.9 15.2 16.4 16.3 17.3 15.6 11.8 6.5 7.4
1909 14.3 10.0 14.8 18.5 15.1 15.7 17.3 16.3 14.9 11.6 14.6 13.0
1910 15.6 7.9 8.3 14.2 13.1 16.2 17.9 18.6 15.2 12.9 11.0 8.6
1911 18.4 10.9 14.9 16.9 14.8 14.0 18.2 19.8 16.2 10.3 11.3 9.8
1912 4.7 5.3 16.1 12.8 13.7 15.3 17.3 15.1 13.3 13.8 8.5 8.6
1913 10.4 9.0 10.5 15.2 13.8 13.2 19.0 17.0 13.6 13.4 12.0 3.6
1914 8.9 4.1 16.8 13.6 16.9 14.9 16.5 16.6 16.8 9.9 11.6 11.2
1915 10.1 11.4 8.0 11.0 12.5 19.4 19.3 16.2 15.1 14.2 12.4 10.6
1916 18.0 10.9 12.3 14.6 18.2 16.5 18.2 16.1 15.9 16.6 15.0 8.2
1917 13.0 7.9 16.7 15.0 15.4 18.1 20.1 16.9 15.9 15.1 11.4 6.8
1918 5.1 11.3 17.0 16.9 17.2 15.7 15.5 17.2 14.1 12.2 10.7 8.1
1919 7.9 5.0 11.1 12.0 12.2 16.8 20.2 16.9 15.5 16.2 13.3 7.6
1920 12.0 10.7 16.3 17.8 17.2 13.9 16.5 16.0 14.2 12.3 11.5 7.8
1921 12.3 3.8 13.6 17.1 16.2 12.1 20.5 16.5 15.5 13.5 7.4 10.6
1922 9.2 16.4 11.4 16.9 15.2 16.7 21.5 16.5 16.9 12.3 11.8 3.3
1923 12.4 11.4 15.4 12.2 15.8 14.0 18.0 15.5 14.9 9.0 7.8 10.9
1924 5.6 6.3 11.5 17.7 14.0 16.5 17.7 16.5 13.0 14.6 8.1 7.9
1925 9.4 4.8 11.4 16.1 11.9 15.7 17.5 18.5 14.9 9.7 9.9 5.5
1926 1.4 2.8 6.1 8.8 12.9 13.7 17.5 15.4 14.8 8.0 6.4 8.9
1927 9.2 0.3 15.0 18.1 17.5 13.3 19.4 15.7 11.8 12.4 11.2 10.5
1928 5.8 5.6 9.5 13.5 13.9 15.0 17.2 17.3 16.0 12.4 6.9 4.1
1929 5.5 7.2 14.6 14.6 13.5 13.1 17.9 16.0 12.1 9.4 11.6 11.0
1930 8.4 6.7 16.9 13.0 13.9 14.6 17.2 17.6 16.2 11.2 12.2 4.0
1931 -1.3 6.4 9.8 13.4 14.1 13.7 16.8 16.5 16.2 13.2 12.7 12.1
1932 12.5 12.3 6.2 11.9 14.5 15.5 17.9 17.4 15.1 12.0 12.0 6.4
1933 12.5 11.3 11.2 14.9 16.1 15.7 19.1 15.7 14.3 11.9 12.5 9.8
1934 4.7 -1.4 7.8 13.3 14.1 16.1 19.3 17.7 13.3 12.1 9.2 8.0
1935 5.9 8.2 13.2 15.8 14.6 13.5 17.9 18.1 13.6 15.9 13.5 1.4
1936 3.2 4.9 14.5 13.1 12.8 14.2 17.7 17.7 15.2 9.6 10.4 12.2
1937 17.4 13.4 11.2 15.4 12.4 12.5 17.4 18.1 15.6 8.5 11.2 6.8
1938 8.4 7.2 11.1 9.9 14.1 14.2 18.7 19.4 13.1 8.7 11.7 5.2
1939 7.6 8.8 13.7 15.3 15.4 16.3 17.1 16.2 14.9 13.9 10.0 0.9
1940 -1.3 1.7 7.0 8.6 14.9 14.7 16.2 16.3 12.8 10.7 10.7 3.1
1941 1.0 2.4 9.5 10.1 15.6 12.7 16.0 15.9 14.0 13.2 12.2 6.8
1942 1.2 6.5 13.7 11.9 14.7 15.0 16.5 14.7 13.4 13.3 15.5 12.3
1943 7.8 10.3 15.8 10.2 15.2 15.0 16.4 17.2 13.9 10.6 6.0 6.0
1944 1.8 10.7 14.5 12.3 13.9 15.2 17.6 17.8 16.8 14.3 7.8 *****
1945 0.4 5.0 11.1 18.4 12.5 16.2 16.2 18.6 14.5 12.9 16.1 4.1
1946 6.7 6.3 13.4 14.6 14.3 15.6 16.5 17.1 14.3 14.2 14.6 13.3
1947 12.8 1.9 10.7 13.0 12.1 14.4 16.9 18.2 16.6 10.5 7.2 9.7
1948 9.1 14.0 16.7 20.7 16.0 15.4 17.2 17.8 15.5 10.8 10.6 14.2
1949 12.0 10.9 6.9 13.5 15.5 16.6 18.8 17.0 13.1 12.4 8.1 10.5
1950 14.9 10.4 8.1 15.5 15.5 15.5 16.2 12.8 12.6 10.8 16.4 8.0
1951 8.3 11.2 15.7 11.9 12.7 14.2 17.9 16.2 12.4 11.5 9.5 13.8
1952 10.4 7.7 14.1 13.7 15.8 14.5 18.4 17.0 14.4 12.4 8.9 3.8
1953 2.5 8.2 14.6 10.4 13.4 17.1 18.2 16.7 15.7 10.5 5.9 8.1
1954 10.8 7.4 16.8 17.5 13.7 13.4 18.1 16.8 15.0 10.7 5.6 11.8
1955 7.1 15.4 16.2 16.6 14.9 15.6 17.0 18.2 16.2 13.1 13.0 11.5
1956 10.2 12.9 14.0 14.2 13.6 15.3 18.8 15.0 13.9 16.2 11.0 7.6
1957 13.8 11.3 7.9 14.9 11.9 12.8 18.6 16.3 11.7 10.7 8.6 12.4
1958 1.0 2.7 14.5 12.5 13.8 14.5 16.4 16.6 14.0 14.6 11.2 5.7
1959 8.4 13.4 12.8 16.1 15.0 14.8 18.4 17.1 12.2 10.4 9.2 10.2
1960 5.9 7.6 13.4 14.8 14.9 16.6 17.0 17.0 16.1 11.9 12.1 5.5
1961 -0.4 6.8 10.3 18.1 15.0 16.4 18.3 15.8 15.8 15.7 12.5 9.8
1962 10.1 7.7 13.3 18.5 18.2 16.8 18.3 17.1 15.6 10.9 8.5 6.7
1963 2.5 2.3 17.4 17.5 15.8 16.3 18.5 16.3 10.7 12.3 11.3 3.2
1964 6.3 10.0 14.6 19.5 20.8 13.8 16.5 16.0 15.0 14.3 12.2 10.7
1965 5.7 10.0 10.9 16.0 16.3 14.2 17.4 15.7 15.0 12.0 13.9 13.3
1966 4.2 12.8 12.2 15.6 16.2 14.0 17.6 16.3 10.3 14.3 15.4 6.7
1967 8.0 8.8 15.8 21.0 18.4 14.4 19.0 14.0 10.2 10.3 12.6 10.0
1968 10.1 0.1 12.3 17.3 16.2 16.2 15.9 15.2 15.9 10.7 6.4 13.6
1969 12.4 8.9 12.9 12.3 12.7 13.2 19.0 16.9 12.2 10.6 10.4 1.8
1970 6.0 2.6 7.9 17.1 16.9 14.6 16.1 16.8 14.3 14.5 14.3 11.9
1971 12.4 7.6 11.2 14.7 14.2 14.5 16.3 15.3 15.3 15.2 11.7 14.2
1972 12.7 10.7 9.8 19.8 14.8 15.5 18.0 14.6 14.8 14.9 9.7 10.7
1973 8.3 8.2 10.6 16.8 14.4 15.1 17.6 17.8 14.3 14.8 14.8 5.3
1974 6.6 11.2 7.4 14.5 15.5 16.0 17.1 14.6 14.4 10.7 10.5 6.1
1975 10.9 8.2 14.4 18.9 14.5 16.6 15.8 17.5 16.5 13.8 12.4 7.0
1976 4.1 13.1 13.8 15.3 14.5 15.8 15.1 15.4 11.8 12.2 7.7 5.1
1977 -1.0 1.2 16.8 16.8 15.6 15.2 17.8 14.0 16.6 11.4 12.5 10.0
1978 0.6 0.6 8.9 14.0 17.6 18.1 17.5 15.2 13.9 12.3 11.2 12.9
1979 6.3 14.2 8.2 15.7 13.4 18.9 16.9 14.2 12.3 8.8 12.5 9.0
1980 6.6 -0.1 10.5 11.3 14.5 18.8 17.1 18.3 14.7 10.5 7.7 5.7
1981 -3.6 5.3 7.0 14.9 13.2 14.9 19.2 15.4 14.5 14.3 8.8 8.2
1982 9.3 11.9 14.8 18.0 16.5 13.3 16.7 17.8 14.8 15.2 9.1 6.0
1983 1.2 -2.3 3.4 16.2 15.5 13.6 17.1 17.8 16.8 14.1 5.0 7.1
1984 6.8 7.5 5.0 15.6 15.5 14.9 18.5 15.7 12.2 12.0 8.0 10.8
1985 0.0 14.2 17.0 17.6 15.6 15.6 17.4 18.1 15.9 15.7 12.5 1.8
1986 1.4 0.5 7.7 18.1 15.3 13.9 17.8 15.4 15.0 11.0 11.9 1.0
1987 3.2 5.5 8.3 12.3 16.5 14.0 15.9 16.6 15.4 12.4 9.7 9.5
1988 5.4 4.2 11.9 13.6 13.5 14.0 17.6 15.6 16.2 11.6 9.8 8.3
1989 12.0 15.0 13.5 16.0 17.4 16.4 18.9 15.9 13.4 14.6 14.0 5.3
1990 7.6 17.5 10.2 15.8 14.4 15.8 16.9 15.1 13.6 14.5 19.1 11.9
1991 7.7 2.7 14.7 14.0 14.5 16.2 16.6 14.9 11.7 13.6 8.4 7.8
1992 -1.1 7.0 10.3 13.9 15.9 13.8 17.3 15.8 15.0 11.7 9.8 13.1
1993 10.8 2.4 7.6 9.7 12.5 15.0 16.9 15.8 15.7 12.5 13.9 6.8
1994 8.3 10.4 12.4 14.0 13.6 16.9 17.2 17.5 13.8 12.7 16.7 5.4
1995 2.2 6.6 11.9 13.9 13.8 14.6 16.8 17.3 10.2 12.9 11.9 -0.3
1996 8.3 8.0 10.9 9.6 15.8 16.7 18.2 18.1 14.6 14.3 12.3 9.8
1997 2.0 4.2 15.0 11.3 12.9 14.7 16.0 16.0 12.5 13.3 10.0 8.4
1998 0.7 0.2 8.1 15.1 15.8 17.7 18.0 18.8 14.5 13.9 9.0 11.4
1999 8.0 6.9 12.0 17.1 15.7 14.0 19.1 14.4 14.3 14.5 11.3 10.5
2000 13.5 0.9 5.9 15.1 16.3 15.4 17.4 18.1 13.4 12.9 9.1 3.2
2001 2.0 9.5
Nov-Mar NP Values (-1000 mb) 1900-1999
00 01 02 03 04 05 06 07 08 09
1900 5.71 10.00 9.48 13.51 12.81 8.48 10.29 14.14 11.82 10.59
1910 11.88 12.78 9.43 9.41 9.07 10.46 12.84 12.16 10.31 8.56
1920 11.98 9.82 11.01 10.86 8.44 8.33 5.14 7.96 8.52 7.67
1930 10.93 6.22 11.15 10.65 6.66 8.91 7.51 12.92 8.94 9.39
1940 3.68 5.35 8.10 12.33 7.80 6.08 9.33 10.67 11.34 10.92
1950 10.39 11.90 11.09 7.60 9.81 11.21 12.30 10.31 7.83 10.30
1960 9.26 6.87 10.68 7.47 9.08 9.89 11.27 10.96 9.02 10.83
1970 5.74 11.48 11.84 9.51 9.06 10.02 10.09 5.95 6.49 10.55
1980 7.69 4.44 10.60 3.46 6.28 10.01 4.79 5.97 8.13 11.74
1990 10.90 11.24 6.45 8.75 10.36 8.56 7.77 8.67 5.48 9.45
2000 8.45 5.96
Mean for 1925-1989 1008.90
Anomalies
00 01 02 03 04 05 06 07 08 09
1900 -3.18 1.10 0.58 4.61 3.92 -0.42 1.39 5.24 2.92 1.69
1910 2.99 3.88 0.53 0.51 0.17 1.56 3.94 3.26 1.41 -0.33
1920 3.08 0.92 2.11 1.97 -0.46 -0.57 -3.76 -0.94 -0.38 -1.23
1930 2.03 -2.68 2.25 1.75 -2.24 0.01 -1.39 4.02 0.04 0.49
1940 -5.22 -3.54 -0.80 3.43 -1.10 -2.82 0.43 1.77 2.44 2.02
1950 1.49 3.00 2.20 -1.30 0.92 2.32 3.40 1.41 -1.07 1.40
1960 0.36 -2.03 1.79 -1.43 0.18 0.99 2.37 2.06 0.12 1.93
1970 -3.16 2.58 2.94 0.62 0.16 1.13 1.19 -2.95 -2.41 1.65
1980 -1.21 -4.46 1.70 -5.44 -2.62 1.11 -4.10 -2.93 -0.77 2.84
1990 2.01 2.34 -2.44 -0.15 1.46 -0.33 -1.13 -0.23 -3.42 0.55
2000 -0.45 -2.94
Special Note: The 2001 seasonal values are based on Nov-Feb.