"Storm glasses contain a mixture of chemicals which are said tocrystallize in a way that makes it possible to predict the eather several days in advance, typically one to three days,"according to Weather Station Advisor. Different kinds of weather--such as rian, snow, storm, frost, and wind, along with changes in ambient temperature-- cause different kinds of crystal formations to form inside the glass, letting you recognize exactly what kind of ourdoor shenanigans are to come.