It's actually somewhat easy... If you are creating financial exposure to an event with no underlying risk to it, and the point is exposure itself, you are gambling.
In your snow example, those guys were gambling on snow for fun. The formal weather derivative - most weather derivatives have parties (usually players in the energy market, sometimes agriculture) who have real underlying risk and aren't entering those contracts to create risk for it's own sake. It's quite hard to get a market off the ground when there is no underlying risk - people purely speculating generally don't generate enough volume to achieve liftoff. Look at Kalshi and the volume on most bets - it's tiny.
In your snow example, those guys were gambling on snow for fun. The formal weather derivative - most weather derivatives have parties (usually players in the energy market, sometimes agriculture) who have real underlying risk and aren't entering those contracts to create risk for it's own sake. It's quite hard to get a market off the ground when there is no underlying risk - people purely speculating generally don't generate enough volume to achieve liftoff. Look at Kalshi and the volume on most bets - it's tiny.