I was reading the manga サマータイムレンダ and was wondering what the "ら" in "明日は雪降ら" mean and come from, most of the characters are speaking 関西弁 so my main theory was to think that it's just a way to say the る in an island dialect but then i realized that the character saying it is also an old man so it could also just be part of an old way of speaking the language, does anyone know more about this ?
I'm not sure of the exact grammar, but aguijonazo's comment suggests that the following is relevant
～するだろう、～しようと思う 例「わえが運転すらー」＝「私が運転しよう」 Weblio和歌山弁辞書
There was also the following from here
ら means similar to the standard う・よう, meaning will, let's. So 雨降ら = 雨が降るだろう = it will rain.
It looks to me like a smartphone hit the old man before he finishes to say a full sentense such as "明日は雪降らんぞ."
UPDATE: Chololate kindly instructed me about the context. "明日は雪降ら" must be a colloquially shortened version of "明日は雪降らあ" which adds an exclamatory tone to "明日は雪が降る," expressing his surprise to see something which would never happen (明日は雪が降るわ>明日は雪降るわ>明日は雪降らあ). Angelo's comment already describes it.