Latent Heat - The heat that is either absorbed or released when a substance undergoes a change of state. In weather, latent heat is an important factor when water changes state between liquid, solid, and vapor. For example, when water goes from vapor to liquid, latent heat is released into the atmosphere. The release of heat during condensation is one of the main energy sources for hurricanes.

Fog - Typically fog is composed of water droplets suspended in the air near the Earth's surface. When bitter cold temperatures are present, fog is composed of ice crystals instead of water droplets, and is called ice fog. Both types of fog reduce visibility at the surface.

Entrainment - The mixing of environmental air into a preexisting organized air current or cloud so that the environmental air becomes part of the air current or cloud. Cumulus clouds are subjected to the process of dry air entrainment on their outside edges. This is why cumulus clouds take on a lumpy and jagged form.

Ceiling - A term that is commonly used in aviation. Ceiling is the height of the lowest layer of broken or overcast skies. This lets pilots know how far above the surface they will be once they get below the cloud layer.

Heiligenschein - A faint white ring surrounding the shadow of an observer's head on a dew-covered lawn. The bright area seen around the head of the shadow is created when sunlight reaches the spherical dew drops and is reflected back up toward the sun. Heiligenschein is the German word for halo.

Diamond Dust - A type of precipitation composed of slowly falling and very small, ice crystals which often seem to float in the air. It may fall from a high cloud or from a cloudless sky. It only occurs during frigid temperatures. Diamond dust is observed around 316 days a year in parts of Antarctica.

Anomalies - Departures of temperature, precipitation, or other weather elements from long-term averages. Any abnormal trend in the weather can be called an anomaly.