The AFD said 1/4", which I was skeptical of. So I immediately came here to check and Rodney lists 0.4", which I find more believable.
The years listed did not include 1996, which I remembered as a summer of rain. But I didn't check the record.
I hope none of the old guys points out that when we were your age the whole summer...well never mind.
(At least we could drink ice water though. With power out, you can't even do that.)
Derecho was my first choice too
Do you have similar data for Baltimore? How about Richmond or Raleigh?
My meaning....if it was meteor dust, as noted, it would not be confined to DC alone.
Fascinating either way.