What's the source of the picture?
It looks like this picture is originally from this article from April. I guess it could have been cold enough for a fire/snow back then? I don't remember if DC had snow in late April…
https://www.washingtonpost.com/politics/with-rallies-banned-joe-biden-welcomes-voters-to-another-kind-of-show/2020/04/25/be7ddd64-8650-11ea-a3eb-e9fc93160703_story.html