Hello David, thank you for reaching out.
Colder temperatures definitely have an effect on battery life. From my experience I have seen about a 10% reduction in range in temperatures between 0 and 32 degrees F. For the long range model Y that usually meant I can expect about a 280 to 290 mile range in those temperatures.

As for a decline when going up mountains, there is definitely a hit but most of it is recouped on the way back down if you use regenerative braking. My usual route into the mountains is about a 30 mile trek to Park City, UT which is a gain of around 2700 feet. In the winter this trip consistently uses about 40–45 miles of battery.

Hopefully that helps answer your questions.