Random but looked at July 2000 (IAD) and oh man it must have been nice: only one 90-degree day (91), 10 highs below 80, and 7 nights in the 50s (with lowest of 50) Departure of -5.4 and 4.28 rain. And look at this stretch:
2000-07-23
78
60
69.0
-8.4
0
4
0.00
0.0
0
2000-07-24
71
64
67.5
-9.9
0
3
0.24
0.0
0
2000-07-25
77
62
69.5
-7.9
0
5
0.00
0.0
0
2000-07-26
71
64
67.5
-9.8
0
3
0.20
0.0
0
Sun coming out now - planning on cooking out later as it will "only" be about 90 today