I was outside with the dogs when it got very still and there was quite a bit of lightning.  I got the "flyable stuff" (umbrella, doggie toys) into the house and shooed the dogs to the basement.  I noticed the mammatocumulus cloud formation first, and my “weather alert” habits from my Air Force career days kicked in.  

We live very close to BWI airport and know the flight patterns, and what is normal and what is not normal.  Then, maybe my 20 years as an Air Force controller experience might color things a little.

At the leading edge, there was turbulence and I noticed a cloud rotation starting to set up.  The next two pictures I took while on the phone to the 911 operators in Anne Arundel county.  

There was ground observable down draft present.  I noted that there was both a very loud wind noise, (that was louder than aircraft taking off).  The cloud rotation was moving from the N-NW rapidly in a mostly Easterly fashion.  There were some wisps of cloud that spiraled down wards, but no funnel developed that I saw.

I went into the basement called your station. Everything was over in a few minutes.