Mean Monthly North American Anticyclone Frequencies, 1950-79

Monthly North American anticyclone climatology for the period 1950-79 is examined. Preferred tracks are evident for each of the 12 calendar months, and three general types can be recognized. The winter pattern is oriented southeastward from northwestern Canada into the contiguous United States; the spring pattern is similar but is displaced eastward, extending southward across western Hudson Bay into the Great Lakes area. The summer pattern develops abruptly in July and has a more zonal orientation east-southeastward from British Columbia along the U.S.-Canadian border. The monthly total of individual anticyclone paths in the study area declined significantly through the period.