Firstly it is strange because of the fore-warning and secondly because of the size of these fireballs.
Apparently there is something happening with an increase in fireball activity worldwide and they are not infact, all caused by meteors...
Four single-engine firefighting aircraft were grounded briefly after a possible meteor was seen in the sky. The Colorado sighting corresponded with reports of a possible meteorite, filed by the crews of two commercial aircraft over Liberal, Kan, said meteorologist Scott Entrekin of the National Weather Service in Boulder.
Fireballs - Weather Plasmas now classified?