How high a percentage of rain does it have to be for you to bring an umbrella?
What does the percentage of rain in the forecast have to be before you decide to bring an umbrella?
ーHow high a percentage of rain does it have to be for you to bring an umbrella?
「傘を持っていくのに降水確率が何パーセントでなければいけない？」
percentage of rain で「降水確率」
bring an umbrella で「傘を持っていく」
ーWhat does the percentage of rain in the forecast have to be before you decide to bring an umbrella?
「傘を持って行こうと決めるのに、天気予報の降水確率が何パーセントでなければいけない？」
forecast で「天気予報」
ご参考まで！
カナダ 
