MILWAUKEE (AP) – School districts across Wisconsin canceled classes as the National Weather Service posted a winter storm warning for much of the state.        Baraboo, Necedah, Wisconsin Dells, Prairie du Chien, Sparta, Tomah, and Marshfield are among the districts calling off school on Wednesday as snow accumulated. The University of Wisconsin-Oshkosh canceled classes beginning at 4 p.m. Wednesday. The heaviest snowfall is expected to fall through mid-afternoon. Strong northwest winds are expected to greatly reduce visibility on state roadways. Accumulations of a-half foot of snow or more are forecast. As of 2 p.m., 7.5 inches of snow was reported 8 miles southwest of Madison.  Dane County sheriff’s officials warned motorists of extremely slippery roads and some near whiteout conditions. Deputies are dealing with numerous accidents.