雹が降っています！
Hyō ga futte imasu!
Hail is falling!
Simple
雹が降っているので、中に入ってください！
Hyō ga futte iru node, naka ni haitte kudasai!
Since hail is falling, please come inside!
ので = because/since, natural reason-giving
雹がゴルフボール大で、車のボンネットがへこんでしまいました！
Hyō ga gorufubōru dai de, kuruma no bonnetto ga hekonde shimaimashita!
Hail the size of golf balls, the car hood has gotten dented!
ゴルフボール大 = golf ball sized; へこむ = to dent; てしまう = unfortunately happened
More Japanese Weather Phrases