23 Pa.C.S. § 5423: Jurisdiction to modify determination.

Except as otherwise provided in section 5424 (relating to temporary emergency jurisdiction), a court of this Commonwealth may not modify a child custody determination made by a court of another state unless a court of this Commonwealth has jurisdiction to make an initial determination under section 5421(a)(1) or (2) (relating to initial child custody jurisdiction) and:

(1) the court of the other state determines it no longer has exclusive, continuing jurisdiction under section 5422 (relating to exclusive, continuing jurisdiction) or that a court of this Commonwealth would be a more convenient forum under section 5427 (relating to inconvenient forum); or

(2) a court of this Commonwealth or a court of the other state determines that the child, the child's parents and any person acting as a parent do not presently reside in the other state.