Civil Dusk - The time at which the sun is 6 degrees below the horizon in the evening. At this time objects are distinguishable, but there is no longer enough light to perform any outdoor activities.

Cumulus - Puffy white clouds that typically have flat bases and have a limited amount of vertical growth. If they start to grow vertically they can morph into cumulonimbus clouds, at which point they can spawn a thunderstorm.

Wall Cloud - A localized, persistent, often abrupt lowering from a rain-free base of a cumulonimbus cloud. The location of the wall cloud marks the location of a strong updraft feeding the storm. Therefore, many wall clouds exhibit rapid upward motion and sometimes rotation. However, not all wall clouds rotate. If the wall cloud is seen rotating, the formation of a tornado is possible.

Cryosphere - This term refers collectively to the portions of the Earth where water is in solid form. This includes areas with snow cover, floating ice, glaciers, ice caps, ice sheets, along with areas of frozen ground. The area of the cryosphere shrinks during the summer season and then grows during the winter.

Blizzard Warning - Blizzard Warnings are issued when visibilities are reduced to a quarter mile or less for 3 hours or longer. Wind speeds must also be sustained at 35 mph with frequent higher gusts in order to achieve blizzard conditions.

Permafrost - A layer of subsoil that remains at a temperature of 32 degrees or colder throughout the entire year. Areas that have permafrost are mainly confined to high latitudes near the poles as well as high mountain ranges. The warming climate that is being experienced on Earth is decreasing the areal coverage of permafrost.

Atmosphere - The layers of gases that surround a planet. The earth's atmosphere is made up of mostly nitrogen, oxygen, and argon. The atmosphere is important in that it helps a planet retain heat at night and also keeps the extreme heat of the sun at bay during the day so that life can survive. Planets with very thin atmospheres have extreme temperature swings from day to night, making them uninhabitable.