The statewide average precipitation of 34.83 inches for the 2001 water year was 3.15 inches greater than the normal annual precipitation of 31.68 inches for water years 1961–90. Average precipitation values affecting streamflow conditions ranged from 92 percent in northeast Wisconsin to 122 percent in southwest Wisconsin with a statewide average of 110 percent (summary tables provided by Lyle Anderson and Ed Hopkins, State Climatology Office, University of Wisconsin, Madison, written commun., 2002).

The year started out very dry with all regions of the state below 50% of the long-term October average. November precipitation, which was approximately normal, was followed by a December which had record-setting snowfall in most of southern Wisconsin and heavier than normal snowfall the rest of the state. This snowfall total was boosted by the colder than normal temperatures that increased the snowfall depth for water content. The state had the first emergency snow declaration since 1979 with 14 counties receiving aid for December snow clean-up (Wisconsin State Journal, Dec. 15, 2001). Statewide precipitation in January was close to normal. February precipitation was above normal in northwest, north central and all of southern Wisconsin. Elsewhere in the state precipitation was close to normal. In March all regions of the state were very dry with total precipitation below 50% of the long-term March average. In April, the northwest corner of the state had precipitation over three times normal, north central had more than double normal and west central also had precipitation significantly above normal. The rest of the state was also above normal. In May, precipitation in the southern and central parts of the state was about 160 percent of normal. From mid June to mid July there was a statewide dry spell, with most of the state receiving less than 1 inch of rain. August precipitation was close to normal for most of the state with some localized very heavy rains of over 11 inches in southwest and south central Wisconsin. In September, the southern part of the state was above normal, the northwest part of the state was below normal and the rest of the state was about normal.

Runoff for rivers in the state ranged from 67 percent of the average annual runoff (1964–2001) at the Kewaunee River site in the northeast part of the state to 160 percent of the average annual runoff (1944–2001) at the Eau Galle River at Spring Valley site in the west central part of the state. Departures of runoff in the 2001 water year as a percent of long-term average runoff in the state (determined using stations with drainage areas greater than 150 square miles and at least 20 years of record) are shown in figure 4.