Isotherm - A line on a weather map joining locations of equal temperature. When looking at weather maps displaying temperatures across the lower 48, isotherms are used to divide the country in different colors based on the varied temperatures. Oftentimes, each isotherm will indicate a change of 5 or 10 degrees.

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.

Bomb - A mid-latitude extratropical cyclone that undergoes a surface pressure drop of 24mb or more during a 24-hr period. Nor'easters are the most common type of rapidly strengthening low pressure systems that can fit the criteria for a bomb low.

Trowal - An acronym for "trough of warm air aloft." It is usually a similar type of frontal structure as is found in the vicinity of an occluded frontal boundary. Organized areas of precipitation can be expected in this region.

Typhoon - A tropical cyclone located in the Northwest Pacific Ocean that has sustained winds of 74 mph or greater. When a typhoon has sustained winds of 150 mph or greater it is called a super typhoon. A super typhoon is only 7 mph short of what would be called a category 5 hurricane if it were located in the Atlantic Ocean.

Tropical Depression - A tropical cyclone with sustained winds lower than 30 knots/35 mph/55kph. The main impacts from a tropical depression would be heavy rain, gusty winds, and a modest storm surge where they make landfall.

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.