NOAA: National Warning GIS Shapefiles

A collection of shapefiles created and compiled by the National Oceanic and Atmospheric Administration. The data is intended to help people understand and predict weather patterns - in particular to plan for potentially dangerous weather conditions such as storms and droughts.

From the site: "The National Weather Service produces short-term warnings to protect lives and property. Four types of warnings (Tornado, Severe Thunderstorm, Flash Flood, and Special Marine) include polygon information at the bottom of the warning, highlighting the primary threat area for the warning. Data from these warnings are collected and databased into a real-time set of GIS shapefiles. These files can be downloaded from this website in order to be used real-time in other Geographic Information Systems applications."