While some snakes are more cold-tolerant than others all snakes are ectotherms meaning that their body temperature is dependent on the temperature of their surroundings.
This means that in general snakes are more likely to be active in warm weather and less active in cold weather.
However there are some exceptions to this rule.
Some snakes like the rattlesnakes and garter snakes are able to tolerate colder temperatures than most other snakes.
This is because they are native to cooler climates and have adapted to be able to survive in cooler weather.
Additionally some snakes like the black rat snake will actually enter a state of dormancy (similar to hibernation) in cold weather in order to survive.
So while it is true that most snakes are less active in cold weather there are some exceptions to this rule.
If you are wondering whether or not a particular snake species is active in cold weather the best thing to do is to research that particular species and see what the experts have to say.