。
The whole town was completely blanketed in snow.
Literal
Town [subject-が] one-surface completely snow [object-を] wore.
一面すっぽり ('entirely, completely covering') combines 一面 ('the whole surface') with すっぽり, a mimetic for something being completely covered or enclosed. 雪をかぶった ('wore snow, was covered in snow') uses かぶる ('to wear on the head, to be covered'). A vivid winter scene.