Anyone who’s tried to make a snowball understands the need for snow of just the right consistency. Start with powdery snow and a ball will fall apart. Start with slushy snow and it will turn into a hunk of ice. The key, then, to a killer snowball is to find snow that’s in the perfect sticky state.
According to Jordy Hendrikx, director of the Snow and Avalanche Laboratory at Montana State University, snow at subfreezing temperatures contains no liquid water. When the grains of ice begin to melt, each one forms a wet meniscus. The menisci work as snowball glue, he says, mingling and then refreezing.