Rain - Precipitation that falls to earth in liquid drops that are greater than 0.5 mm in diameter. Liquid drops that are smaller than .5 mm are categorized as drizzle. The largest raindrop that has ever been measured occurred in September of 1995 in Brazil as well as in July of 1999 in the Marshall Islands. At both these sites the raindrops were measured at a whopping 8.6 mm (.338 in) diameter!

Freezing Drizzle - A drizzle that falls as a liquid but then freezes into a light glaze or rime upon contact with the cold ground. Freezing drizzle is different than freezing rain because it accumulates at a much slower rate. Freezing drizzle tends to be localized and not widespread, which makes it more difficult to predict.

Greenhouse effect - The term that describes how the Earth receives solar radiation and how it is essentially trapped in the Earth's atmosphere. The incoming solar radiation is absorbed at the surface and then radiates back up to space in the form of infrared radiation. However, the greenhouse gases in the atmosphere absorb some of this outgoing radiation and then re-radiate it back down to the surface. The higher the concentration of greenhouse gases, the more magnified this effect becomes.

Terminal Velocity - The maximum velocity that can be reached for a falling object. Terminal velocity is reached when the downward force of gravity and the upward force of air resistance become equal to each other. An object's fall speed becomes constant once it reaches terminal velocity. The terminal velocity of most raindrops is around 20 mph, while large hailstones have terminal velocities that can exceed 100 mph!

Drought - An extended period of abnormally dry weather that creates shortfalls in the amount of surface and/or subsurface water. Droughts have major impacts on agriculture and can have major socioeconomic consequences as well.

Rossby waves - Also known as planetary waves. Rossby waves are a series of long-wavelength troughs and ridges that occur along the main branches of the jet stream. They form due to the rotation of the Earth and are an important way for the planet to distribute heat away from the equator as well as cold air from the poles.

Skew-T - A Thermodynamic Diagram on which temperature, dew point, and winds are plotted for the various levels in the atmosphere. Meteorologists receive the data needed to construct a skew-t diagram from weather balloon launches. Skew-t charts are a great way to diagnose how stable or unstable the atmosphere is on a given day.