Ann Arbor’s climate is mostly continental and is strongly influenced by the movement of high and low pressure systems across the continent. It experiences larger seasonal temperature ranges than areas closer to the Great Lakes which have moderated temperatures. Prevailing westerly winds deliver some lake effect precipitation to the area, but it is essentially limited to increased cloudiness during the late fall and early winter. While the day-to-day weather is highly variable, prolonged periods of hot, humid weather in the summer or extreme cold during the winter are relatively uncommon. Precipitation is welldistributed throughout the year, although the wettest months of the year tend to occur during the warm season. Summer precipitation comes mainly from afternoon thunderstorms.
Summary of Observed Changes
Rising average temperatures: Annual average temperatures warmed by 0.7°F from 1951-2014, slower than regional, national, and global rates. Average low and high temperatures have warmed at approximately the same pace.
Longer freeze-free season: Despite warming average temperatures, the freeze-free period of the year has actually shortened slightly, by approximately 4 days, from 1951-2014.
More precipitation: Total precipitation increased 44.2% (13.4 inches), from 1951 through 2014. Winter increases over that time exceed 75% (4.4 inches).
More heavy precipitation: The number of very heavy precipitation events has increased by 21.1% (comparing the 1951-1980 total to the 1981-2010 total).