Wear your thermal underwear to "Snow Angels," a wintry drama in which the small-town clime is so frigid and gray, you could easily catch your death.

Based on a novel by Stewart O'Nan, writer-director David Gordon Green's brave and magnificently performed period piece (mid-'70s) witnesses an adolescent's first romance as it blossoms amid a dissonant backdrop of disintegrating marriages.

Michael Angarano plays Arthur Parkinson, a mush-mouthed high schooler who finds himself drawn to a new girl in town, Lila (Olivia Thirlby), at the very moment that his father is moving out of the house. The tense breakup of his parents runs smoothly compared with the messy estrangement between Arthur's former baby sitter, Annie (Kate Beckinsale), and her husband, Glenn (a sensational Sam Rockwell), a born-again Christian who is coming apart following the separation.

While Arthur and Lila perform an awkward mating dance, Annie spurns Glenn's attempts at rapprochement. When Annie is not working at a local Chinese restaurant, she leaves her young daughter with her mother so she can indulge in motel trysts with her co-worker's husband, Nate (a drolly dull-headed Nicky Katt).

If the elements are fairly standard-issue "Peyton Place," Green ("George Washington" and "All the Real Girls") is a wizard at generating urgency from the seeds of small-town angst. He juxtaposes the film's multiple cross-currents with an even hand, with one critical exception: Green overplays Glenn's descent, to the point that we become impatient for the film's inexorable conclusion.

By contrast, "Snow Angels" is peppered with detailed supporting turns that leave us wanting more, including the wonderful Jeannetta Arnette as Arthur's attentive mom and a creditably serious Amy Sedaris as Annie's betrayed co-worker.

Green exits on a mildly hopeful note of youthful romance, yet one feels overwhelmed with sadness at the knowledge that, like the surrounding snowbanks, its days may be numbered.