Cool, Wet Start to May

The first half of May was both cool and wet. Preliminary data indicates that statewide temperatures were 1.4 °F below normal for the period May 1-17. Meanwhile, precipitation has been abundant. The statewide average precipitation was 4.15 inches, 1.79 inches above normal or 176 percent of normal. The heaviest rains have fallen in western and northern Illinois. The largest month-to-date total reported was 8.24 inches in Dallas City (along the Mississippi River between Quincy and Moline) by a CoCoRaHS observer.

Table 1. Precipitation totals by climate division in Illinois, along with the 1971-2000 normals, and percent of normal, for May 1-17, 2009.
Climate Region Precipitation (in) Normal (in) Departure (percent)
Northwest 4.64 2.25 206
Northeast 4.55 2.06 221
West 5.84 2.46 238
Central 4.17 2.32 179
East 3.17 2.21 143
South Southwest 4.26 2.43 175
South Southeast 3.67 2.46 149
Southwest 3.37 2.49 135
Southeast 3.51 2.66 132
State 4.15 2.36 176

Illinois was surrounded on three sides by very wet conditions in parts of Missouri, Iowa, Wisconsin, as well as Kentucky. The rains in Illinois have produced saturated soils in places and minor to moderate flooding along the Mississippi and Illinois Rivers and their tributaries.

May 1-16 precipitation
Precipitation totals for the Midwest for the period May 1-16, 2010 (click to enlarge).
May 1-16 percent of normal precipitation
Percent of normal precipitation across the Midwest for May 1-16, 2010 (click to enlarge).

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