Illinois State Water Survey - University of Illinois at Urbana-Champaign

State Climatologist Office for Illinois

Cloudiness in Illinois

Dr. Jim Angel, State Climatologist

Illinois has never been considered the Sunshine State. However, cities in Illinois are considered in the middle ranks of U.S. cities in terms of cloudiness. They are neither as sunny as Las Vega nor as cloudy as Seatle.

Here is a breakdown of the number days of clear, partly cloudy, and cloudy days, for the few sites in Illinois with long-term observations. Hourly weather observations of cloud types and coverage (in tenths) are combined into daily values. The daily average sky cover is assigned to three classes. Daily average sky cover ranging from 0 to 3 tenths is considered "clear". Daily average sky cover from 4 to 6 tenths is considered "partly cloudy", and from 7 to 10 tenths is considered "cloudy".

Table 1. Annual Average Number of Days by City
City Clear Partly Cloudy Cloudy
Cairo 113 104 149
Chicago 84 105 176
Moline 101 100 164
Peoria 95 97 172
Rockford 93 98 174
Springfield 104 94 167

Here is the Excel spreadsheet containing the monthly and annual average cloudiness for Illinois locations.

Here is the link to the NCDC page on cloudiness of US cities.

Illinois State Water Survey

2204 Griffith Dr
Champaign, IL 61820-7463
217-333-0729
jimangel@illinois.edu

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