Site that tells why flags are at half-staff?

On my way to school this afternoon, I passed Union Station (in Washington, DC) and noticed that the flags were at half-staff. This was both the station and the surrounding Federal buildings. When I got to school, I asked around and not only did few people notice, but no one had a definite answer. Perhaps because Walter Annenberg, a former ambassador to Britain, died?

Though I am curious about today, the GQ I am posting is a bit more general. Is there a site that posts the reasons and durations of half-staff orders? I can sometimes find individual press releases, but I am looking for somewhere I can check whenever I see them down and don’t offhand know why. Thanks.

Rhythmdvl

IIRC, a member of the US Congress just passed away.

Flag Etiquette - 36 USC 10

Also see US Flag.org