It is the heaviest in as many as five decades.这是五十年来最严重的一次。

　两个地方需要注意。第一，“五十年”，这里用的词是decade（十年）；第二，“在五十年中”，不要丢了介词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.
　　在许多地区，大雪已连续下了很多天，积雪被称为五十年来最严重的一次。