– Showers covering more than 54 percent of an area.

– National Weather Service.

– A complex frontal system that occurs when a cold front overtakes a warm front. Also known as an occlusion.

– Ocean waters from 60 nm to 250 nm.

– A term used to describe vertical motion in the atmosphere. The “omega equation” used in numerical weather models is composed of two terms, the “differential vorticity advection” term and the “thickness advection” term. Put more simply, omega is determined by the amount of spin (or large scale rotation) and warm (or cold) advection present in the atmosphere. On a weather forecast chart, high values of omega (or a strong omega field) relate to upward vertical motion in the atmosphere. If this upward vertical motion is strong enough and in a sufficiently moist airmass, precipitation results.

– A wave of low pressure that does not have a complete circulation around it; also called a short wave trough.

– The vertical forcing of air by terrain features such as hills or mountains. This can create orographic clouds and/or precipitation.