adverb
suddenly; abruptly; unexpectedly
Describes a sudden, often surprising change or occurrence. Commonly used in the phrase にわかには信じがたい (hard to believe suddenly).
空がにわかに曇って、雨が降り出した。
The sky suddenly clouded over and it started to rain.
その知らせはにわかには信じられなかった。
I couldn't believe the news all of a sudden.