What is lip-synching? Typically, a musical performance is recorded in a studio specifically designed for sound recording. This is so the best quality sound is recorded. Then, at a later event, which might be outside or in some other context where good sound or a precise performance is difficult, the performer mimes the performance to a playback of the recording. Here, let's let Beyoncé show us how it's done:
The reasons for lip-synching an outdoor performance in January in Washington, DC are obvious. As Yo-Yo Ma said, it is standard procedure when you can't afford a mishap. Cold outdoor weather is not kind to delicate musical instruments and even less so to delicate vocal cords!
But if the authenticity of the performance is more important than the perfection of the performance, sometimes you might see performers playing outside, on a windy roof, in January: