All photochromic lenses are temperature-dependent. Temperature affects the degree to which your lenses darken and the speed with which they clear again.
In cold temperatures, photochromic lenses will get darker. At very high temperatures, photochromic lenses will not be as dark due to the thermal process affecting the molecules. This is a normal reaction for photochromic lenses.
Experts recommend that wearers exposed to extreme conditions (beach, watersports, skiing...) consider a second pair of polarized prescription sunglasses.