Translation:It snowed last night.
降る (ふる) is a 五段 (ごだん or five-base) verb, when it conjugates the final syllable changes. In the case of 降る, the polite past-tense becomes 降りました. If you wanted to give the plain past-tense you would use 降った. Not all of the 五段 verbs have the same past-tense form, so pay attention when conjugating from the root or dictionary form to past tense.
To provide an example in a different verb base, 食べる (たべる) is an 一段 (いちだん or one-base) verb, when it conjugates you remove the final る syllable and replace it with the intended ending. 食べました for polite past-tense and 食べた for plain past-tense.
Lissie, the verb furu is to fall and in Japanese weather forecast, same as ib Scotland, they merely specify what is falling down and when. http://123japanese.com/index.php?cmd=lessons&menu=weather