G

Gale warning – sustained wind speeds from 34 to 47 knots (39 to 54 mph).

Glaze – a layer or coating of ice that is generally smooth and clear, and forms on exposed objects by the freezing of liquid raindrops.

Global warming – a theory that increased concentrations of greenhouse gases are causing an elevation in the Earth's surface temperature.

Good visibility – more than 10 kilometers.

Greenhouse effect – the warming of the atmosphere by the trapping of longwave radiation (heat) being radiated to space. The gases most responsible for this effect are water vapor and carbon dioxide.

Ground fog – shallow fog (less than twenty feet deep) produced over the land by the cooling of the lower atmosphere as it comes in contact with the ground. Also known as radiation fog.

Gust – a brief sudden increase in wind speed. Generally the duration is less than 20 seconds and the fluctuation greater than 10 miles per hour. In Canada, gust is defined as a sudden, brief increase in wind speed that generally lasts less than 20 seconds. In Australia, gust is defined as any sudden increase of wind of short duration, usually a few seconds.

Gustnado – gust front tornado. A small tornado, usually weak and short-lived, that occurs along the gust front of a thunderstorm. Often it is visible only as a debris cloud or dust whirl near the ground.