Bram Greenberg, age 11, of Allentown, Pennsylvania, for his question:

Why does it hail only in summer?

Hail forms in thunderstorms and in most parts of our country, we expect these weathery squalls to strike us during the hot, sultry days of summer. But thunderheads follow different schedules in other parts of the world. Over the oceans, they strike most often in winter and during the night. The seas get pelted with hailstones most often during the dark nights of winter.

Hailstones tend to form only in certain weather conditions and these conditions are most likely to occur in thunderstorms. The storm area must be a whirling turmoil of wet and dry, warm and cool masses of air. There must be a wide range of temperature called a steep temperature gradient. In the thunderheads that pelt us with summer hail, the temperature gradients range from cool to very warm. In winter. thunderstorms over the seas, hail is formed in steep temperature gradients that range from very cold to mildly cool.