Thank you for posting that link Davidmaria. However for the uninformed, the page, and specifically text "National bank holidays and weekends are taken into account." is misleading. One would assume that Thanksgiving Day would constitute a national bank holiday, however the Oanda page states that the "FX Markets" are open in New York only.
Spreads generally correspond to liquidity, at least if you're not with a bucket that intentionally widens spreads at key moments.
If you were less blind/stupid/trying too hard to make yourself look less dumb, you'd see that it indicates NY as CLOSED (in bright red letters) when it would otherwise be open until 5:00ET.