A notable increase in precipitation, moderate rain days, thunderstorm days, and hail days has been occurring since 1925 at La Porte, Ind. Since La Porte is 30 miles east of the large complex of heavy industries at Chicago, there is a strong suggestion that the increases in precipitation conditions are due to inadvertent man-made modification.

If these increases are real, they serve as a good measure of the increase in convective precipitation that man could attain, at the same time pinpointing an excellent site for future meteorological studies of the exact causes of the increases. If the increases are fictional and result from exposure changes and observer error, they serve as an indication of the sizeable errors that may exist in some of our long-term climatological records.

The increase at La Porte is sizeable: during the 1951–1965 period La Porte had 31% more precipitation, 38% more thunderstorms, and 246% more hail days than did surrounding stations. Since 1925 the year-to-year fluctuations in the annual and warm season precipitation at La Porte show agreement with the temporal distribution of steel production in the Chicago area. After a careful assessment of all available climatological data, it was concluded that these sizeable increases were real and not fictional.

This content is only available as a PDF.