NEW YORK — The post-holiday slide snowballed into an avalanche in Week 34 (Jan. 15-21), with total Broadway grosses dropping about $2.5 million to $14.8 million.Except for the strong-selling “The Coast of Utopia” and Manhattan Theater Club’s previewing “Translations,” all of the 27 offerings on the boards saw a dip in sales. And some of those dips were worryingly large. “The Color Purple,” for instance, plummeted nearly $250,000, drawing just 51% of capacity. Two other tuners from last season, “The Drowsy Chaperone” and “Tarzan,” also saw sizable drops in receipts. Long-runners felt the chill, too, as they usually do when tourists trickle away from the city. “The Lion King,” “Beauty and the Beast,” “Hairspray” and “Rent” were among the perennials to fall off at the box office. Meanwhile, “Mary Poppins” is maintaining its holiday momentum, hanging on to the third-place slot behind “Wicked” and “Jersey Boys.” Also staying strong is “Spring Awakening,” which saw only a slight dip of about $10,000. Fellow arthouse tuner “Grey Gardens” fell around $40,000. Among the plays, things looked good for “Utopia,” but “The Vertical Hour” played to 64% capacity and “The Little Dog Laughed,” which shutters next month, was down to 47%. Overall, though, Broadway came out a little ahead of the same frame last year, when sales dipped to approximately $14.2 million. The 23 musicals grossed $13,719,484 for 92.8% of the Broadway total, with attendance of 180,491 at 73.9% capacity. The four plays grossed $1,057,972 for 7.2% for the Broadway total, with attendance of 25,964 at 80.6% capacity. Average paid admission was $76.01 for musicals, $40.75 for plays and $74.53 for all shows.