わっと

adverb

suddenly and loudly; burst out

Describes a sudden, loud outburst of sound or emotion, such as crying, laughing, or shouting. Often used with verbs like 泣く, 笑う, or 叫ぶ.

• 赤あかちゃんがわっと泣なき出だした。

  The baby suddenly burst out crying loudly.

• 会かい場じょうからわっと笑わらい声ごえが起おこった。

  A loud burst of laughter erupted from the venue.