I use Weather Underground for the my weather needs, especially the handy-dandy web-mapping application for “Is it going to rain on my run?” weather report. Just recently, I was checking the radar before heading out and noticed what appeared to be a technical malfunction, or the opening scenes to an epic movie.
What is happening? Were there massive, freak storms happening throughout the eastern US? No.
What you are probably seeing are radar blobs/radar blooms. It took a couple minutes of Googling, but here is a 2007 article from AccuWeather.com explaining what you see on the map. Apparently I observed a phenomena actually known as Ground Clutter. I’m neither a radar or weather expert so I won’t comment on what is technically happening but it’s still pretty neat to see on a map.