The National Weather Service has confirmed that an EF-0 tornado with winds of 70mph touched down near Allentown and Auth Roads by Andrews Air Force Base on Wednesday evening. The 100 yard wide twister was on the ground for about a minute and crossed onto the base before lifting.
Here is a video from a storm chaser of the tornado: Andrews AFB Twister, 4/27/11 (WARNING… video contains crude language.)
