Tropic of Capricorn - The Tropic of Capricorn is an imaginary line of latitude going around the Earth at approximately 23.5 degrees south of the equator. It is the southernmost point on Earth where the sun's rays can be directly overhead. On the day of the Northern Hemisphere's winter solstice, the sun will be directly overhead at noon here.

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.

Trough - A sharpened zone of cyclonic wind change usually associated with a zone of lower pressure. Troughs can occur at the surface up to around 30,000 ft up in the atmosphere. Deep troughs in the mid to upper levels tend to be associated with surface frontal boundaries and surface low pressure systems. Inclement weather can be expected when a trough moves through a particular area.

Radiational cooling - The cooling of the earth's surface that occurs at night when the absorbed heat from the sun that occurred during the day radiates back up to space in the form of infrared radiation. Radiational cooling is maximized during clear nights when there are light winds.

Knots - The unit meteorologists use to measure winds speeds. Knots are the common unit pilots and sailors use when gauging wind speeds. A knot is based on nautical miles rather than statute miles. A wind speed of 1 knot is equal to 1.15 mph.

Drizzle - A type of precipitation consisting of numerous tiny droplets of water less than 0.5 mm in diameter. Drizzle typically falls when there is fog or low stratus cloud cover over an area.

sounding - A sounding is the graphical output taken by a rawindsonde which is launched with a weather balloon to record various atmospheric variables in differing altitudes. Temperature, moisture, and wind speed/direction are most commonly measured when a sounding is taken. The data can be plotted on a diagram called a skew-t diagram which can give important details on the atmosphere such as how stable or unstable it is.