We'll have to see how the next few winters play out, but I think it's not unreasonable to think the urban core (parts of DC, Arlington, Alexandria) will move into the USDA 8b hardiness zone (annual min temp between 15-20F).
lol see above. it's going on 1000+ days now. It probably ended this hour.
We still have a streak ongoing of days reaching at least 30F that stretches back to the beginning of Feb 2019.
there was one summer day in the middle of the 2010s - I don't know if you all remember it, but the mid atlantic and NE had INSANELY high dewpoints. I think Dover, DE was up in the mid 80s. I'm pretty sure both Central Park and DCA cracked 80F. JFK had an hourly ob with a dewpoint of 84F lol. That day was probably my max - I just remember any aerobic activity outside being a real struggle.
There was another afternoon when we had just moved to DC and a t-storm was passing just to our north. It was far enough away to keep our air temp in the mid 90s but it pushed the dewpoint up to around 84 (per my local weather station). I was running at the time and that was not easy.
cold air damming is still pretty fierce down there and storm tracks are typically such that they get big warm layers overhead (hence freezing rain). You move north, the less likely you have such layers. You move south, and that wedge isn't as strong.