More torrential rain and flash flooding are expected in waterlogged South and Midwest / More torrential rain and flash flooding expected in heavily waterlogged South and Midwest / US prepares for deadly floods with many National Weather Service offices understaffed / South and Midwest face potentially catastrophic rains and floods while reeling from tornadoes / What to know about the severe storms and flash flooding hitting parts of the U.S. / What to know about the severe storms and flash flooding hitting parts of the US / U.S. South and Midwest hit with deadly storms and tornadoes, as threat of flash flooding looms / Tornadoes, floods threaten Midwest as storms wallop region and the South / Storms could unleash deadly floods, strong tornadoes in large part of US in coming days