Synoptic Scale and Air Masses

Synoptic Scale

The synoptic scale is the level just below the global scale. It is what we call the "weather map" scale because the highs, lows, and fronts that you see on weather maps fall into this scale. The synoptic scale encompasses regions thousands of miles in area with circulations that last from days to weeks. We will look at four major items on the synoptic scale: air masses, fronts, cyclones, and anticyclones.

Air Masses

An air mass is a very large body of air which has fairly uniform temperature and moisture properties throughout its horizontal extent, which may cover thousands of miles. Air masses originate in source regions, where the air is relatively stagnant and the air can acquire the properties of the source region. For example, the Canadian interior is a source region for the cold air that gives New England its first deep freeze in the autumn. An air mass that forms in the Bermuda region is what brings the Carolinas their hot, humid summers. There is a simple scheme of four classifications that are combined to describe an air mass's properties. A "c" stands for "continental", meaning that the air mass developed over land. An "m" stand for "maritime", meaning the air mass formed over water. A "P" stands for "polar", meaning the air formed over the cold polar regions. A "T" means the air mass formed over a warm "tropical" region. These four are combined to describe air masses according to the table below:

Symbol	Classification	Description
cP	continental polar	cold, dry, stable
cT	continental tropical	hot, dry, stable air aloft; unstable air at surface
mP	maritime polar	cool, moist, unstable
mT	maritime tropical	warm, moist, unstable

Air masses move from their source regions to the US and bring us their weather. The transition zone between two unlike air masses is called a frontal zone, which we discuss next.

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