It looks like there are increased water and ice spawns for the event

I've seen plenty of them in a park, they're everywhere there, and it wasn't even a nest, they're permanent residents just like Nidorans.

But in other news, apparently Feebas, Spheal and 18 other things are here.
And Santa Hat pikachu.

I'm always amazed by how different biomes can be. Jynxes are sort of like Murkrows for me...they are super common, and only worth the trouble to catch if they have a very high or very low CP (for usability or easy stardust, respectively). My pokedex says seen 253, caught 159, which indicates I clicked on a lot of them and then decided not to bother trying to catch them. I know that there are probably hundreds more that I didn't even bother clicking on.

If you've never seen a wild jynx you haven't been playing long.