Precipitation that falls to earth in drops more than 0.5 mm in diameter.
A dark, horizontal cloud base with no visible precipitation beneath it. It typically marks the location of the thunderstorm updraft. The base may not actually be precipitation free with hail or large rain drops falling under it.
A region of dry air subsiding on the back side of, and wrapping around, a mesocyclone. It often is visible as a clear slot wrapping around the wall cloud of a supercell thunderstorm
The ratio of the amount of water vapor actually present in the air to the greatest amount possible at the same temperature, usually expressed as a percentage.