All thunderstorms start off as a cumulus cloud, the fleece white cloud of summer days. However when the conditions are right, this normally docile cloud can continue to rise, and as the day gets hotter, form into a cloud known as the cumulus congetus, or Towering Cu. When the top of the cloud gets way on up there it starts to freeze, and we see the tops of the cloud go from a cauliflower shape to a more fuzzy shape as ice crystals form. Don't think for a minute freezing at the top of a cloud is the same temperature that water freezes at the earth's surface. At any rate, ice forms at the top of the cloud and we can have all kinds of interesting phenomenon such as hail, rain, lightning, and down burst.
Wind shear is change in wind speed with direction and height.
Most of the rain in thunderstorms is melted hail. When the cumulonimbus cloud develops it's anvil, it is also when lightning develops do to processes beyond the scope of these notes. Lightning can strike between cloud and ground, cloud to cloud and inside the thunderstorm itself. All thunderstorms have downdrafts at some stage in their lives, but microburst, also known as down burst have winds of 57mph or greater. This down draft of cold air is caused by storm hail falling through the cloud and forming a large area of cold air.