NWS Summary of November 17 Tornado Outbreak

The image shown here is a time-lapse of the tornado that ripped through Washington, IL on November 17, 2013. The colors show precipitation intensity (called a "reflectivity" image). The pattern of precipitation formed a distinct "hook" shape (larger version of image), indicating the thunderstorm had developed rotation (a mesocyclone) on its SW side. Rotation does not guarantee that a tornado will form, but it it a precursor - and this one did spawn a tornado. Evaluation of the aftermath indicated the intensity reached EF-4 as it moved through Washington, IL (aerial photos). Amazingly there were only 2 deaths in the city of over 15,000. Cell phone warnings alerted many who were in church. CLICK HERE to see/read other storm summary resources posted by the National Weather Service. This Wikipedia page is another good source. Also, check out this RADAR PowerPoint presentation that I have posted.