Year,Value,Contiguous U.S. (Lower 48),Clouds,Apr,(%)
1940,59.982
1941,62.638
1942,60.473
1943,56.13
1944,60.425
1945,55.362
1946,47.559
1947,57.041
1948,53.741
1949,52.464
1950,53.313
1951,52.924
1952,49.283
1953,54.261
1954,53.558
1955,51.058
1956,53.207
1957,60.347
1958,56.836
1959,53.545
1960,51.802
1961,50.746
1962,47.443
1963,55.458
1964,52.468
1965,57.954
1966,54.311
1967,54.709
1968,49.217
1969,48.903
1970,52.598
1971,45.857
1972,50.847
1973,53.988
1974,51.465
1975,55.942
1976,51.065
1977,47.686
1978,55.587
1979,55.541
1980,50.156
1981,54.805
1982,53.354
1983,55.807
1984,53.003
1985,48.167
1986,52.759
1987,45.611
1988,51.244
1989,52.006
1990,55.47
1991,57.081
1992,56.222
1993,59.05
1994,54.773
1995,56.857
1996,53.343
1997,56.334
1998,48.857
1999,55.288
2000,48.928
2001,53.499
2002,53.906
2003,52.76
2004,51.403
2005,49.214
2006,49.303
2007,52.622
2008,46.467
2009,51.708
2010,52.262
2011,54.135
2012,50.189
2013,53.672
2014,55.975
2015,53.907
2016,52.813
2017,59.722
2018,53.653
2019,59.643
2020,50.317
2021,48.349
2022,51.596
2023,50.546
2024,49.467
2025,51.564