English Translation
This summer we had an unusual amount of rain.
普通でなかった is an unusual expression in this context.
今夏は例年を大幅に上回る（or 下回る）雨量だった。（こんかはれいねんをおおはばにうわまわる/したまわるうりょうだった）
is more natural. 例年 means “average in the past years”. 例年 is frequently used when something is compared with the average seasons.