Everything You Ever Wanted to Know about Precipitation in Illinois, Illinois State Water Survey

Precipitation in Illinois

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Infrared photograph of a hail damaged corn field
Infrared photograph of
a hail damaged corn field
A hailpad sensor (left) and recording raingage being serviced
A hailpad sensor (left)
and recording raingage
being serviced
Pattern of a crop-damaging hailstreak
Pattern of a crop-
damaging hailstreak
Lake effects on annual precipitation
Lake effects on annual
A large thunderstorm cloud over the Mississippi and Missouri Rivers near East St. Louis
A large thunderstorm
cloud over the Mississippi
and Missouri Rivers
Snowfall and freezing rain areas from a model
Snowfall and freezing
rain areas from a model
View ALL Photos
and Graphics


            Since 1947, precipitation investigations at the Illinois State Water Survey (ISWS) have been extensive, as would be expected at a water resources agency. As a result, every aspect of precipitation in Illinois has been better described, defined, and explained than for any other location on Earth.

            These intensive studies of all aspects of precipitation provided data and information about this key component of the hydrologic cycle for design and operation of water control and management structure, for weather and climate modification, and for a diverse user community, including Illinois agriculture. These studies fall within seven categories:


     1.    Studies of historical data to define climatological fluctuations in space and over time.

     2.    Studies of precipitation variability across 1–1,000 square-mile areas using 25 networks of densely spaced recording raingages located in all parts of the state.

     3.    Studies of 34 record-setting 1- to 2-day rainstorms since 1951 using field data and also defining storm scale and risks.

     4.    Development and testing of instrumentation to measure precipitation, including raingages, weather radars, cameras that recorded raindrop sizes, hail sensors, and laboratory facilities for assessing raindrop growth and interactions.

     5.    Microscale, cloud scale, and mesoscale assessments of the physics of rainfall formation.

     6.    Studies of nonliquid forms of precipitation (hail, snow, and sleet).

     7.    Assessments of changes in precipitation amounts due to cloud seeding, inadvertent modification by urban areas and industrial complexes, or climate change.


            This enormous endeavor has required highly diverse and dedicated meteorologists, climatologists, engineers, technicians, field staff, and data analysts. That the ISWS was able to assemble and train these talented individuals was a major accomplishment, but the ISWS precipitation studies program also resulted in numerous scientific and organizational achievements. These include:


          Obtaining more than $40 million of external funding from federal agencies and private industry.

          Awards from the American Meteorological Society, American Geophysical Union, and American Society of Civil Engineers for innovative ISWS projects and publications.

          Characterization of time and space dimensions of heavy rainfall frequencies in Illinois that revealed important temporal changes during the 20th Century and the effects of large urban areas on storms and local rain frequencies and flooding.

          Development of creative new instruments: area integrator for radar interpretation of rainfall amounts, raindrop camera, hail sensors, special radars (CHILL and HOT), and cloud physics laboratory equipment for cloud and raindrop studies.

          Recognition as a national leader in precipitation studies, particularly ISWS expertise in hydrometeorolgy.

          Development of new measurement techniques, such as aerial infrared photography to measure crop-hail losses, now widely used by the hail insurance industry.

          Discovery and definition of new weather elements: hailstreaks, hailstripes, global raindrop size climatology, rain cells, and thunderstorm interactions that produce record rainstorms.


Illinois State Water Survey

2204 Griffith Dr
Champaign, IL 61820-7463

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