がさっ
gasa'

To-Adverb

1. with a swoosh; at one fell swoop

Onomatopoeia
よる あいだ屋根 やね もった ゆきがガサッと ちてきた。
yoruno aidani yaneni tsumotta yukiga gasatto ochite kita.
The snow that had piled up on the roof at night came down with a thud.
Other forms: