Air mass - A generic term for describing areas of the atmosphere that have similar origins, along with similar temperature and moisture qualities. The two main types of air masses are tropical and polar. Polar air masses are typically cold and dry, while tropical air masses are inherently warm and humid.

Frontolosis - The dissipation of a frontal zone due to a weakening contrast between two air masses. The temperature gradient weakens during frontolysis, meaning the rate of change of the temperature along the frontal boundary is lessening. At the end of frontolysis, the front no longer exists. The opposite of frontolysis is frontogenesis.

El Nino - An anomalous warming of ocean waters in the east central equatorial Pacific. El Nino events occur every two to seven years and have local as well as global impacts. Nutrient deficient waters cripple the fishing industry off the coast of western South America during El Ninos, while global weather patterns can be significantly altered due to the presence of an El Nino.

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.

Isobars - Isobars are lines on a weather map joining points that have the same air pressure at a given altitude. Isobars are typically drawn in for surface plots. When isobars are tightly packed, windy conditions can be expected.

Blue Jet - An upper-level atmospheric electrical discharge, usually blue or bluish-white in color, that occur high above thunderstorms. Similar to sprites. This phenomenon is believed to connect the tops of thunderstorms with the ionosphere.

Perihelion - The point on the annual orbit of a body (about the sun) that is closest to the sun; at present, the earth reaches this point on about 5 January. Opposite of aphelion.