ASK TOM: Chicago's longest string of rainy days

Dear Tom,
I have a new calendar that says Chicago had 60 straight days of rain starting on April 1, 1858. Is that correct?
– Jay Taylor, Chicago
Dear Jay,
The report is suspect, and verification is impossible because of the year in question, 1858, pre-dates Chicago’s official precipitation records that did not begin until Nov. 1, 1870. Prior to that, we have monthly but not daily precipitation totals, so it is impossible to know how daily rainfall was distributed. However, April, May and June of 1858 were wet months (3.1, 7.8, 6.3 inches respectively). Indirect evidence strongly suggests that 60 consecutive days with precipitation is highly unlikely. In 142 years of official records, the longest string of “wet” (0.01 inches or more) days is only 19, beginning on Dec. 28, 1945, and another beginning on Dec. 15, 1961 — far short of the 60 consecutive days alleged in 1858.