When sims work as a lifeguard, the game randomly picks the beach for them to patrol in the course of their duties. In towns where winter is enabled, the lifeguards still have to go out in the snow and cold to rescue beachgoers. Why they’re going out to the beach when it’s so cold out is a different question, but even with several inches of snow on the ground, the lifeguard still has CPR to administer to unlucky sims.
The lifeguard sim will get cold from being outside all day, so give him the immune to cold lifetime reward when he can afford it. He’ll need it for days like this.