Third period collapse costs Merrimack in loss to Notre Dame

Notre Dame 5, Merrimack 4

Nolan Flamand drives the net in the second period against Notre Dame (Owen McMahon/TMR)

NORTH ANDOVER — Third periods have been the Warriors’ undoing, and the numbers paint a stark picture.

Through the first 12 games of the season, Merrimack has outscored opponents 23-16 (+7) across the opening two periods. But when the third period arrives, the script fl…