2.2.1 Climate

The climate is predominately continental.  Sitting close to the middle of North America, the weather in the watershed can vary widely and rapidly.  Both temperature and precipitation can change abruptly.

The watershed’s climate is shaped by two well-defined systems.  Strong southerly winds from the Gulf of Mexico are the main source of moisture.  A diffuse secondary system from the Pacific Ocean also adds to annual rain and snowfall.  Air masses carrying the moisture that eventually falls in the watershed may travel nearly 1,500 miles.  A minor change in the wind system can, therefore, result in the watershed getting well above or below normal annual amounts of rain or snow.

The watershed’s seasons generally vary along continental patterns.  Spring, summer and fall are normally very pleasant (see Table 4 for historic temperature data).  The watershed’s sub-humid summers have ample rain for garden and farm crops.  Long spells of hot and humid weather do not visit the area very often.  The area’s 160-day growing season allows most crops to mature before the autumn freeze.

Table 4.  1971-2000 temperature normals for the Minneapolis-St. Paul and Maple Plain areas.

(Degrees Fahrenheit.)

Minneapolis/St. Paul
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Maximum 21.9 28.4 40.6 57.0 70.1 79.0 83.3 80.4 71.1 58.4 40.1 26.4 54.7
Minimum 4.3 11.8 23.5 36.2 48.5 57.8 63.0 60.8 50.8 38.9 24.8 10.9 35.9
Mean 13.1 20.1 32.1 46.6 59.3 68.4 73.2 70.6 61.0 48.7 32.5 18.7 45.4
Maple Plain
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Maximum 23.1 28.7 41.0 57.4 70.7 78.1 82.8 80.3 71.7 58.9 40.9 27.5 55.1
Minimum 2.8 9.6 21.7 34.4 47.4 56.0 60.0 57.6 49.1 37.0 23.7 10.0 34.1
Mean 13.0 19.2 31.4 45.9 59.1 67.1 71.4 69.0 60.4 48.0 32.3 18.8 44.6

Source: Minnesota State Climatology Office and Midwestern Regional Climate Center.

In a normal year, around 30 inches of precipitation falls on the watershed.  Table 5 shows the watershed’s historic annual precipitation.  Winter snowfall averages about 56 inches in the lower subwatershed, with a little less falling in the western areas.  Snow generally stays on the ground from mid-December to early March

Table 5.  1971-2000 precipitation totals for the Minneapolis-St. Paul and Maple Plain areas (inches).

Minneapolis/St. Paul
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Precipitation 1.0 0.8 1.9 2.3 3.2 4.3 4.0 4.0 2.7 2.1 1.9 1.0 29.4
Snow 13.7 8.2 10.5 3.1 0.1 0 0 0 0 0.6 10.0 10.1 56.3
Maple Plain
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Precipitation 0.9 0.7 1.7 2.4 3.5 4.7 4.2 4.0 3.4 2.5 1.6 0.9 30.5
Snow 11.8 7.1 9.5 2.8 0.1 0 0 0 0 0.3 6.6 10.7 48.9

Source: Minnesota State Climatology Office and Midwestern Regional Climate Center.

Ice covers Lake Minnetonka for about five months a year.  The average date of ice-out is April 15.  Table 6 lists the ice-out dates for Lake Minnetonka from 1918 to 2005.

Table 6.  Lake Minnetonka ice out dates, 1855-2005.

Date of Ice Out Date of Ice Out Date of Ice Out Date of Ice Out
1855 - April 18 1910 - March 27 1943 - April 12 1976 - April 3
1856 - May 8 1911 - April 1 1944 - April 23 1977 - April 10
1857 - May 5 1912 - April 13 1945 - March 30 1978 - April 17
1858 - March 30 1913 - April 18 1946 - April 2 1979 - April 23
1859 - May 4 1914 - April 17 1947 - April 19 1980 - April 19
1860 - April 4 1915 - April 17 1948 - April 11 1981 - March 27
1861 - 1876 - Unknown 1916 - April 19 1949 - April 13 1982 - April 19
1877 - April 14 1917 - April 18 1950 - May 2 1983 - April 22
1878 - March 11 1918 - April 14 1951 - April 28 1984 - April 13
1879 - 1886 - Unknown 1919 - April 6 1952 - April 22 1985 - April 13
1887 - April 14 1920 - April 17 1953 - April 8 1986 - April 8
1888 - April 25 1921 - April 3 1954 - April 12 1987 - March 21
1889 - April 1 1922 - April 17 1955 - April 12 1988 - April 7
1890 - April 16 1923 - April 23 1956 - April 21 1989 - April 17
1891 - April 21 1924 - April 24 1957 - April 20 1990 - April 4
1892 - April 11 1925 - April 7 1958 - April 11 1991 - April 8
1893 - April 28 1926 - April 18 1959 - April 10 1992 - April 10
1894 - April 9 1927 - April 12 1960 - April 16 1993 - April 19
1895 - April 5 1928 - April 18 1961 - April 14 1994 - April 11
1896 - April 5 1929 - April 7 1962 - April 25 1995 - April 3
1897 - April 18 1930 - April 5 1963 - April 10 1996 - April 24
1898 - April 18 1931 - April 6 1964 - April 13 1997 - April 18
1899 - April 24 1932 - April 14 1965 - May 1 1998 - April 3
1900 - April 16 1933 - April 18 1966 - April 4 1999 - April 2
1901 - April 23 1934 - April 10 1967 - April 9 2000 - March 18
1902 - April 1 1935 - April 7 1968 - April 1 2001 - April 19
1903 - April 13 1936 - April 20 1969 - April 17 2002 - April 16
1904 - April 25 1937 - April 19 1970 - April 19 2003 - April 12
1905 - April 2 1938 - April 9 1971 - April 17 2004 - April 6
1906 - April 16 1939 - April 17 1972 - April 26 2005 - April 9
1907 - April 8 1940 - April 25 1973 - April 4  
1908 - April 12 1941 - April 14 1974 - April 19  
1909 - April 26 1942 - April 4 1975 - April 28  

Source: The Freshwater Society.