How many days do we have precipitation in Chicago?

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Dear Tom,

I am curious as to how many days we have precipitation in Chicago.

Melissa Andrews

Dear Melissa,
A review of Chicago’s precipitation records for the entire period of official records, 1871 through 2016, reveals that measurable precipitation (0.01 inch or greater) falls on 125 days per year, or one day out of three. The precipitation is not spread evenly through the year, however. It’s most frequent in the spring and least frequent, usually, in the autumn and winter. September averages least days per year, with 8.2, and April the most, with 11.8. Precipitation of 0.01 inch is very light, and is likely not to be noticeable. Somewhat heavier precipitation, 0.10 inch or greater, ranges from 4.6 days in February to 7.1 days in May, and heavy precipitation, 1.00 inch or more, ranges from two tenths of a day in February to 1.0 days is August.

It should be noted that these figures are merely averages; precipitation occurrences in Chicago’s rough-and-tumble climate often vary greatly from the averages in any given year. In the years from about 1970 onward, heavy precipitation totals have been occurring more frequently in the late summer and early autumn (especially August and September).

Precipitation intensity is important also. Cold-season precipitation ends to be long-duration, though of light intensity. Snow, whose water content is usually less than rain, tends to last longer. And summer thunderstorms, while often delivering greater rainfall totals, are usually of relatively short duration.

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