Severe thunderstorm and flash flood threat forecast across much of theMidwest, Tennessee and Lower Mississippi valleys, as well as into parts ofthe Southern Plains over the next few days......Heavy snow to impact the Northern Rockies with well below averagetemperatures throughout much of the Rockies and Intermountain West......Triple digit and potentially record-breaking heat over southern Texason Wednesday and Thursday...A mature and vertically stacked low pressure system over the NorthernPl...