Type distributions of precipitation at selected stations in Illinois

All the precipitation which fell during a ten‐year period at four first‐order weather stations in Illinois is classified according to its source from one of six major types of precipitation systems: (1) cold front; (2) warm front; (3) stationary front; (4) squall line; (5) warm air mass; and (6) cold air mass. The amount of precipitation and the frequency of occurrence for each of the six major types by monthly totals are presented in tabular and graphic form. Squall lines and warm air mass showers are shown to be of much greater importance at Cairo than at the stations farther north.