Definition of Synoptic Weather Map

Definition of Synoptic Weather Map
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Synoptic means "view together" or "view at a common point". A synoptic weather map shows weather patterns over a large area by putting together many weather reports from different locations all taken at the same moment in time.

What is a Synoptic Weather Map?

A large scale pressure system
••• Image by, courtesy of Ethan Hein

In a synoptic weather map, local and regional weather observations are put together on a map covering a large area, typically between 620 miles (about 1000 kilometers) to 1500 miles (2500 kilometers), but often larger, such as a synoptic weather map of the United States. This large an area is the scale in which high and low pressure systems operate.

How Time is Referenced

Different time zones
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Since synoptic meteorology is concerned with viewing weather over large areas at the same time, a common reference point for time is needed. Using Greenwich Mean Time, also known as UTC (“Universal Time Coordinate”) as the starting point, each reporting time zone is identified by its offset from UTC. For example, on the East Coast of the United States, Eastern Standard Time would be -5 UTC because the time in that time zone is five hours after UTC.

Features of a Synoptic Weather Map

High, low, or front?
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A synoptic weather map will show areas of high pressure marked with an “H,” areas of low pressure marked with an “L,” and fronts, which are the leading edges of current weather systems. Some synoptic weather maps show “isobars,” which are concentric lines around a high or low weather system indicating the system’s wind strength.

What are Highs and Lows?

Low pressure systems can bring rain
••• Image by, courtesy of Chris Metcalf

High pressure systems generally indicate fair weather and little precipitation. Low pressure systems indicate colder temperatures and are usually accompanied by clouds and precipitation. Since these features operate over large, regional areas, they normally persist for days or weeks.

How does a Front Affect the Weather?

Weather fronts bring change
••• Image by, courtesy of Kevin Dooley

A weather front is a transition zone or interface between two areas of different pressure and temperature. In a cold front, cold air is replacing warm air on the earth’s surface. Likewise, in a warm front, warm air is replacing cold air on the surface.

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