Report from my father from this morning (so, pre-whatever's about to start): It must have been quite some storm last night. I rode down into the park this a.m. and I was blocked by water on the bike path from Rock Creek both ways within a mile of the beltway.
Rock Creek was flowing just below the bottom of the bike path bridge coming up the hill out of the park, so I biked back up the road I had come down into the park on.
I haven't seen that much flooding in the almost 45 years I have been biking in the park.