Gamma rays - a type of electromagnetic radiation with a very short wavelength and high Energy level. Generally, emitted during radioactive decay of a substance.

Gas - one of the three basic phases of matter; a gas can expand indefinitely to completely fill its container

Gas Constant - the proportionality constant in the equation of state for ideal gases; for dry air, the gas constant is 287.054 joules per kilogram per Kelvin

Gas Laws - the thermodynamic laws pertaining to perfect gases, including Boyle's law, Charles' law, Dalton's law and the equation of state

General Circulation - the typical atmospheric weather patterns over the earth

General Circulation Model (GCM) - a type of numerical model used in Numerical Weather Prediction that represents a forecast of the long-term (e.g., months or years in the future) changes in the atmosphere globally

Geostationary Satellite - a satellite that orbits the earth at a height and velocity which allows it to remain over a fixed place above the equator

Glacier - a large body of ice moving slowly down a slope or valley or spreading outward on a land surface

Glaciation - the condition that exists when land is covered with glaciers

Global Radiation - the total direct solar radiation and diffuse sky radiation (e.g., that reflected or scattered) received by surface of the earth

Global Scale - the largest scale of planetary motion; covering all or most of a latitude circle in horizontal extent

Gradient - in general, the spatial change of a physical quantity (e.g., temperature)

Graupel - snow pellets or soft sleet

Gravity - in particular, the force imparted by the earth which tends to draw all bodies in the earth's sphere of influence toward the center of the earth

Graybody - a hypothetical "body" that absorbs some constant fraction of all electromagnetic radiation incident upon it

Greenhouse Effect - see atmospheric greenhouse effect

Greenhouse Gases - the gases that absorb terrestrial radiation and contribute to the greenhouse effect; the main greenhouse gasses are water vapor, methane, CO₂ and ozone.

Greenwich Mean Time (GMT) - global time scale based on the local time observed on the Prime Meridian; also called Zulu (Z) time or Universal Coordinated Time (UTC)

Ground Clutter - a pattern of radar echoes from fixed ground targets (buildings, hills, etc.) near the radar. This contamination is processed into the NEXRAD base products (base reflectivity, base velocity, and spectrum width) and affects all derived products. Ground clutter is most prevalent close to the radar at the lowest elevation slices. Ground clutter is always present around the radar and is not the same as anomalous propagation (AP), which occurs during certain atmospheric conditions.

Growing Degree-Day - a form of degree-Day used as a guide to determine the most appropriate time to plant and harvest crops

Gulf Stream - a warm, swift, relatively narrow ocean current that flows along the east coast of the United States

Gust Front - a boundary between cold air from the thunderstorm downdraft and warm, humid surface air

Gustnado (or Gustinado) - [Slang] a small tornado, usually weak and short-lived, that occurs along the gust front of a thunderstorm