A weather system that produces snowy, unsettled weather.
Low pressure troughs are weather systems that produce snowy, unsettled weather. Global winds generate wavy atmospheric flow patterns, forming ridges and troughs of atmospheric pressure. On a weather map that shows upper level atmospheric pressure, a low pressure trough is the U-shaped portion of a wave. Longwave troughs are a broad-scale feature: they can span most of the US. Shortwave troughs are minor waves embedded in larger features: they often span the area of a US state or less. Troughs direct cooler, unstable air over a region, often trailing an associated cold front with them. The leading edge of the trough, where the cold front is located, is the most active part of the system and is where the heaviest snowfall commonly occurs.