The official site has a release calendar up:

ARCH 4
STF: The Infected
MARCH 18-24
STF: The Cure
MARCH 18-31
Update 1 (Title TBD)
APRIL 1-7
STF: Khitomer Accord
APRIL 8-14
STF: Undine: Terradome
APRIL 22-28
STF: Children of Khan