They haven't done a "flash mob" performance this year, but this performance at the Washington National Cathedral is mighty fine.
https://www.youtube.com/watch?v=Q41ctPLDHvU
And for jazz lovers, the 2015 World War II flashback performed at Union Station in Washington, DC, USA, is worth a look:
https://www.youtube.com/watch?v=khQN5ylb3H0&t=9s
Don