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 heaviest snowfall is expected from 8 a.m. to 2 p.m. Strong northwest winds are expected to greatly reduce visibility on state roadways.  Accumulations of a-half foot of snow or more is forecast.    In southeastern Wisconsin, joggers traded shorts for warmer gear as temperatures plummeted from records highs Tuesday and rain turned to snow.