Rain Gauge - An instrument used to measure the amount of rainfall that occurs over a specific site. A standard rain gauge can measure up to 8 inches. The first known device that was used for measuring rainfall was invented in Korea in 1441.

GFS (Global Forecast System) - One of the American operational forecast models run at the National Centers for Environmental Prediction. GFS stands for Global Forecast System. The GFS model is run 4 times a day and it covers the entire globe. GFS forecast output can extend up to 384 hours from when it is run.

Equinox - Time of year when day and night are nearly equal in length. The equinoxes signal a transitional time of year. In the northern hemisphere, the autumnal equinox is the transition season that leads up to winter. Conversely, the vernal equinox is the transition season of spring that leads to summer. On the equator, the sun can be seen directly overhead at noon on the day of an equinox.

Computer Model - A system of computers which run complex physics equations on meteorological data to produce mathematical forecasts. Forecast models are first initialized with the current conditions in the atmosphere, and then thru a series of complex algorithms, they model what will be happening anywhere from 12 to 180 hours from the current time. There are several computer models that meteorologists utilize in predicting the weather.

Backing wind - Winds that change direction in a counterclockwise sense. This occurs when wind directions turn to the left. An example is when the winds at a specific location turn from the north to the northwest. Backing winds can also refer to how the winds change direction with height. An example of this is when winds at the surface are from the north, while winds aloft are from the northwest.

Nimbostratus - A cloud characterized by grey featureless layers of clouds that is almost uniformly dark gray. This type of cloud typically produces precipitation and the base of the cloud is usually below 8000 feet. They are commonly seen when frontal systems move through a region.

Anemometer - An instrument that measures wind speed. The strongest wind speed ever recorded by an anemometer was 253 mph during the passage of a cyclone on Barrow Island, Australia back in April of 1996.