Accuracy of Chicago’s early weather records

Pricey Tom,
You’ve talked about that Chicago’s climate data started in 1885. I’ve all the time questioned how correct these data are as compared with at present’s.
— Evangelene, Arlington Heights

Pricey Evangelene,
Accuracy within the early days of climate observations was not a problem. Chicago’s official data date from Nov. 1, 1870 (not 1885), when the Climate Bureau (now the Nationwide Climate Service) started operation. Observations initially consisted of day by day excessive and low temperatures and precipitation, and have been extraordinarily correct. Temperatures have been recorded to tenths of a level from mercury-in-glass thermometers, however now temperature readouts are isolated indoors from outside sensors which might be dependable solely to a level or two and require occasional recalibration. Precipitation measurements, taken manually then and now, are correct.

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