A low pressure center located in the mid and upper levels of the atmosphere which moves from west to east within the jet stream. These disturbances are also called upper level troughs or short-wave troughs. A clock wise turning with height along with an increase of wind speed with height is a key ingredient for the development of supercell thunderstorms given a high degree of atmospheric instability. A lowered cloud base under a thunderstorm. Wall clouds that rotate around a vertical axis are called low-level mesocyclones and may be precursors to funnel clouds and potential tornadoes.
Wind direction is measured from which it's blowing.