umulus 
One of three basic cloud forms, this particular form is best known for its vertical development. Cumulus are billowy clouds that often have flat bases. 

owndraft 
A sudden descent of cool or cold air to the ground, usually with precipitation, and associated with a thunderstorm or shower. The opposite of an updraft. 

ry Line 
The boundary between the dry desert air mass of the Southwest and the moist air mass from the Gulf of Mexico. It usually lies north-south across the central and southern High Plains states during spring and summer. The passage of a dry line results in a sharp decrease in humidity, clearing skies, and a wind shift from southeasterly or south to southwesterly or west. Its presence influences severe weather development in the Great Plains. 

ust Front 
The leading edge of the cool, gusty surface winds produced by thunderstorm downdrafts. 

recipitation 
All forms of water, liquid or solid that falls from clouds and reaches the ground. This includes drizzle, freezing drizzle, freezing rain, hail, ice crystals, ice pellets, rain, snow, snow pellets, and snow grains. 

ubsidence 
A sinking or downward motion of air, often seen in anticyclones. It is most prevalent when there is colder, denser air aloft. It is often used to imply the opposite of atmospheric convection. 

upercell 
A severe thunderstorm characterized by a rotating, long-lived, intense updraft. Although not very common, they produce a relatively large amount of severe weather, in particular, extremely large hail, damaging straight-line winds, and practically all violent tornadoes. 

pdraft 
A small scale current of air with vertical motion. If there is enough moisture, then it may condense, forming a cumulus cloud and possibly thunderstorms. The opposite of a downdraft. 

ind shear 
The rate of wind speed or direction change with distance. Vertical wind shear is the rate of change of the wind with respect to altitude. Horizontal wind shear is the rate of change on a horizontal plane.