Azores High - Also known as the Bermuda high, this is a large, persistent, atmospheric high-pressure center that develops over the subtropical region of the eastern North Atlantic Ocean. The position of this high will migrate between Bermuda and the Azores Islands throughout the course of a year.

Hail-Spike - A radar signature that can occur when severe hail is present in a thunderstorm. The signature is seen as a narrow line of weak reflectivity beyond the thunderstorm. Its occurrence is due to the way the radar pulse is scattered in many directions when it reaches large hailstones. This phenomenon is also referred to as the three-body scatter spike.

Hygrometer - An instrument designed to measure the water vapor content and relative humidity in the atmosphere. Leonardo da Vinci built the first version of a hygrometer back in the 15th century.

Radiation Fog - This type of fog forms at night under clear skies with calm winds. Under these conditions heat that was absorbed by the earth's surface during the day is allowed to radiate back into space. As the earth's surface continues to cool, provided a deep enough layer of moist air is present near the ground, the humidity will reach 100% and fog will form. Radiation fog varies in depth from 3 feet to about 1,000 feet and is always found at ground level and usually remains stationary. This type of fog can reduce visibility to near zero at times and make driving very hazardous.

Advection - The transfer of an atmospheric property by wind. The most common entities that meteorologists look at when diagnosing areas of advection are temperature and moisture.

Eddy viscosity - The turbulent transfer of momentum by eddies giving rise to internal fluid friction. Eddy viscosity is an important concept in turbulence theory.

Hydrosphere - The hydrosphere is composed of the sum of all the water on Earth. This includes all the Earth's surface waters such as oceans and lakes, as well as all sources of frozen water. Water vapor and therefore clouds are also included in the hydrosphere.