It is possible that your raynauds has a vasospasm component to it and the cold weather exacerbates it (causes the vasospasming to occur or makes it worse). Perhaps that is why your Dr gave calcium channel blocker ---- to stop the vasospasm.
An example of what I mean by "upstream": Lets say someone has TOS and is prescribed opiates for pain. This may help with the pain, but it won't deal with the problems of TOS. Opiates for pain is more downstream than drugs for, say --- neuroinflammation and neurosensitivity (if they existed). If you were given drugs to treat that, it would have a better effect on your TOS situation because neuroinflammation, etc is more upstream than pain. Prolly not the best example, but just trying to illustrate what I mean.

I hope you don't have TOS and the calcium channel blocker is all you need. Take care.