Lee-Side - The term lee-side in general refers to the sheltered side from the wind. In weather, this term is used when referring to the sides of a mountain range. The side that takes the prevailing winds first is known as the windward side, while the side opposite the prevailing winds is the lee-side. The lee-side of the Rocky Mountains is to the east of the mountain range.

Astronomical Twilight - Is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening, scattered light from the Sun is less than that from starlight and other natural sources. Before and after astronomical twilight, the sky is absolutely dark.

Mountain Breeze - A wind pattern that develops during the night due to differential cooling on the mountain compared to nearby valleys. The mountain cools faster than the valleys in the evening. This cool, dense air blows down the mountainsides into the valleys. The opposite occurs during the day, which produces an upslope wind known as the valley breeze.

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.

Rawinsonde - An instrument attached to a weather balloon that measures atmospheric pressure, temperature, humidity, and wind speed/direction at different layers of the atmosphere. As the instrument rises through the atmosphere, the data is sent via radio waves to a receiver on the ground. Rawinsondes are launched all over the world at specified times. The data from these launches is used in initializing the numerous forecast models.

Doppler Effect - The shift in frequency that occurs when an object goes from moving towards an observer to away from an observer. Everyone has heard this when a police car drives by. As the police car is approaching, the siren will have a high pitch. Then when the police car begins moving away from you the pitch of the siren lowers. This effect is what weather radars use to calculate velocity.

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.