Figure 4. Convection in a cumulonimbus cloud, viewed here perpendicular to wind direction, follows the shear angle. Rising warm air moves upward and to the left, the upshear side, while sinking cooler air moves downward and to the right, the downshear side. Precipitation falls out on the downshear side. In this example the winds aloft are sufficient to blow the top of the cloud off, forming an “anvil” consisting almost entirely of ice particles.