National Weather Service
To keep an eye on weather warnings in near real time, check the interactive national weather map put out by the National Oceanic and Atmospheric Administration's National Weather Service (NWS).
Warnings are color-coded by type of alert. Simply click on your area of interest to see details. Or search for a forecast by state, city/state or zip code.
The NWS site offers Active Alerts, Forecast Maps, and Radar, as well as information on Rivers, Lakes, Rainfall; Air Quality; Satellite; and Past Weather.