I wonder if this extreme cold will kill any fish.
When did they start calling cold snaps a POLAR VORTEX?

Or is this something new?

I think the possibility is there for some fish to not make it through this colder than usual temps. Usually they would be fine unless it was a long period of time before the temp rises again. So as long as the temp goes back to normal with a couple of days, it shouldn't do much harm at all.

I haven't heard them call this a Polar Vortex before so it's new to me. I usually hear them refer to it as an Arctic Front or Arctic Blast.

Maybe tilapia?

Unless in a power plant lake, I would bet the tilapia are in real trouble. Some shad are not able to survive really cold temps. Threadfin shad start to die off if the water temps get to 45 degrees or lower. Gizzard shad are more tolerant of cold water.

Never heard grandpa say there's a Polar Vortex a coming

Weather people getting bored putting names on everything.