fishtailing in the snow on 2014 chevy Impala-how can I eliminate?

Better tires for the snow, tire chain or buy a 4x4 or all wheel car.

Go slower?

Neither answer was enlightening.

What do you want us to say. There isn't much to do to a car in the snow. Assuming the car's steering, suspension and brakes are in good working order. It's all traction (tires and or chains) or driver skill. Fish tailing a fwd car in snow means your are going too fast around a corner or hitting the brakes too much letting them lock up. Rolling tires give traction, if they lock up they slide whatever direction they want to.

How about additional weight in the trunk ?

How old are you?

Higher than your I.Q.

My guess is you have an LTZ with performance rims, pretty typical for that year. Tires are limited as far as all seasons performance, and what you can get aren't very forgiving on wear if tire out of balance or misalignment isn't attended to promptly. I have the Goodyear Eagle RS-A tires on mine as OEM from day 1, and they too are not good traction tires in snow or wet roads. Cooper makes a decent hybrid performance/ all seasons tire, their LSR by Master Craft (Cooper bought them out). Not as good as most all seasons tires, but better than the Eagle RS-A. And they're rated for 70,000 miles.

I have an LT and thank you for your answer.