Indian Summer - A period of unseasonably warm and sunny weather that occurs from late September to mid November. In parts of the country, the first killing frost of the season must occur before a late autumn warm spell can be coined 'Indian Summer'.

Cloud Modification - The introduction of foreign particles by humans into a cloud to gain a desired effect. This is oftentimes called cloud seeding. Silver iodide is a common substance that has been used in cloud seeding. The desired impact is to increase the amount of precipitation and/or reduce the threat for hail that falls from the cloud. It is not known how effective cloud modification has been since it was first introduced in the late 1940s.

Diamond Dust - A type of precipitation composed of slowly falling and very small, ice crystals which often seem to float in the air. It may fall from a high cloud or from a cloudless sky. It only occurs during frigid temperatures. Diamond dust is observed around 316 days a year in parts of Antarctica.

Arctic Front - The semi-permanent, semi-continuous boundary that separates the deep, cold arctic air from the shallower, less frigid polar air of the northern latitudes. Major shifts in the polar jet stream can drive arctic fronts southward into the mid-latitudes during the winter season.

Meridional flow - Meridional flow is a term that describes the direction of the upper level wind flow with respect to the Earth. When the upper level winds oscillate from north to south often, a meridional flow pattern is present. The opposite of meridional flow is zonal flow. In zonal flow, the upper level winds move in a more west to east fashion.

Virga - Any precipitation that is falling from the clouds, but doesn't make it to the ground. The reason that virga occurs is due to dry air that the precipitation cannot penetrate through to make it to the ground, as it evaporates into that layer. Meteorologists can verify virga by looking at where radar data is showing precipitation and then looking at nearby surface weather observation sites to see if any precipitation is being reported.

DAPE - An acronym that stands for Downdraft Available Potential Energy. This is a measurement of a thunderstorm's ability to produce strong currents of descending air that reach the surface, called downdrafts. Thunderstorms with high levels of DAPE, can produce intense downdrafts that can result in straight-line winds of over 100 mph.