NEW ORLEANS — Powerful storms killed two people in Mississippi, tore the roofs off an apartment building and a nursing home in a small town in Oklahoma and threatened more communities across the nation Tuesday with wide-ranging weather. The large storm system also brought blinding dust storms to the Southwest, blizzards with whiteout conditions to the Midwest and fears of wildfires elsewhere. In Irving, Texas, a tornado with winds up to 177 kph struck, while another touched down in the 16,000-resident city of Ada, Oklahoma, according to preliminary information from the National Weather Service. There were also two tornadoes in