Apple Watch Series 3 ski tracking
There's still no ski tracking capabilities in any of the Apple Watch series. 

But, all the data inputs needed are there. Barometer, motion tracking, heart rate tracking, location via GPS and cell tower trilateration, etc...

After the initial announcement, Apple referenced that this feature would be available toward the end of 2017, probably before winter.  

The HomePod IPSW leak a few months ago provided some indication that Apple would add this feature to Workouts.  This screen grab shows there's references to skiing workouts already built into the firmware.


For now, you can use the myriad of different ski tracking apps out there.