It is the heaviest in as many as five decades.
這是五十年來最嚴重的一次。
----------------------------------------------------------------------
兩個地方需要注意。第一，“五十年”，這里用的詞是decade（十年）；第二，“在五十年中”，不要丟了介詞in。
原句是：
In many areas, where snow has continued falling for several days, the accumulation has been described as the heaviest in as many as five decades.
在許多地區，大雪已連續下了很多天，積雪被稱為五十年來最嚴重的一次。
海納百川，有容乃大；壁立千仞，無欲則剛。