Advection Fog - Advection fog often looks like radiation fog and is also the result of condensation. However, the condensation in this case is caused not by a reduction in surface temperature, but rather by the horizontal movement of warm moist air over a cold surface. This is very common during the winter when warm moist winds blow over cold snowcover. Advection fog may also form when moist maritime air masses drift over a cold inland area. This usually happens at night when the temperature of the land drops due to radiational cooling.

VIL - This is an abbreviation for "Vertically Integrated Liquid." This is a quantity that can be shown on a radar display. It is an estimate of the mass of precipitation in the air. It is given in units of kilograms per square meter. High VIL totals tend to indicate large hail or very heavy rainfall.

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.