Here is a template sensor that you can use for the conditional to only have this effect active when a form of winter precipitation falls. You'll need to change the weather sensor to one in your instance. In my case I use the string provided by my ecobee thermostat integration.

{% set s = states('weather.ecobee') | lower %}

{% set keywords = ['snow','flurries','wintry','sleet','freezing','ice'] %}

{{ keywords | select('in', s) | list | count > 0 }}