Buffalo Niagara International is in Cheektowaga, about 11 miles east of downtown. Several airlines fly nonstop to both cities.
For D.C., that means Reagan National, Dulles or BWI. Reagan has its own Metro station. BWI has a rail station, with MARC and Amtrak trains to Union Station.
For New York City, it's JFK, LaGuardia or Newark. NJ Transit and Amtrak stop at Newark's rail station.
Rather stay on the ground? Amtrak runs a few trains a day from Buffalo to Penn Station along the Empire Corridor. It's a long day, most of the daylight, with most of the state going by the window.
Driving is about 375 miles to either city, so make it a Thursday drive and be settled before the 8:45 start on Friday. Eyeing a Phoenix date on the cards above? Those trips may need a connection.
What May and October Feel Like
D.C. in May: highs in the mid 70s, lows near 60, a few rainy days. Buffalo is still in the upper 60s then, nights in the 40s, so D.C. feels like early summer. Pack a light layer and a rain layer.
New York City in October: highs in the 60s, cooler nights. Home runs around 60 with nights in the 40s, so one jacket covers both ends. Lake-effect snow is a winter thing, and neither trip lands in winter.