I was lucky to get this very interesting cloud formation at sunset when I was at the National Mall during my only visit to Washington DC.
(Sony A65, ISO 100, f/8, 17mm [25mm equiv.], 1/400s)
This photo was taken in October of 2015. I was in DC for just a weekend, and I spent most of the time at the Mall, going from museum to museum. I really need to go back some time.