November-December 1998, Vol. 86, No. 6

Figure 8. Orientation of a cumulonimbus anvil to other developing convection (seen in plan view) may determine whether new thunderstorms develop. When the anvil overtops newer convection (a), ice particles fall from the anvil and seed newer convection below, preventing water vapor from reaching altitudes where it can become supercooled. But when the anvil blows away from newer convection (b), the system is free to develop and may become electrically active.