Yes, it's too cold now (I'm also in NE). Next spring, either replace the railing with one that is made with pressure-treated wood, prime, and paint, or if you want to hang onto that railing, sand it down until it's smooth, use BONDO, building it up and sanding it until it's where you want it, then prime it, and paint it.

Bondo dries VERY quickly, so you only want to use the amount you need at the time. Do a thin layer, then when that dries, sand it, then mix another blob of Bondo, do another layer, and so on until you have it as you want it.

Thanks so much! Since it's only one spot I think I'd prefer to probably just fix it in the spring for the time being. Under neath that peeling part is a plastic type screw that holds both posts together. Will it be ok to fill that with bondo? This is all new to me so I appreciate all feedback!

A plastic screw???

No. Take the screw out, then do the Bondo thing (don't worry about filling the screw hole), then prime, paint, drill a new hole, and use a stainless steel screw. You always want to be able to unscrew something in case you need to replace that one thing, for instance one board on a deck, or just the railing in your case, or the post the railing is attached to, etc., etc.