12.+Synoptic+chart+interpretation

__12. **Synoptic chart interpretation - wind direction, speed, pressure patterns, rainfall and fronts** __ 

By Darren Low

This is a wind 'arrow' on a typical synoptic chart. The line represents direction. The direction is found by the direction the line is coming from in relation to the orientation on the map. It is always interpreted as from the direction it is coming from. Example: in the diagram above the wind is a northeasterly. The speed is determined by the 'notches' on the back of the arrow.
 * 1. Wind Direction and speed**


 * 2. Pressure Patterns**

Atmospheric pressure varies with both height above mean sea level, and from place to place at mean sea level. Lines on a weather map joining places of equal mean sea level pressure are called isobars. On a daily weather map there will be meandering patterns of relatively high and low pressure systems. It is these systems that generate variations in wind, temperature and rainfall. In particular the direction and speed of the wind is closely related to the distribution of mean sea level pressure.

Two types of pressure systems: Low pressure, and high pressure


 * 3. Rainfall + Fronts**

Rainfall is measured in millimetres and is usually represented on a colour scale or chloropleth map.

Fronts are defined as the transition zone between two air masses of different density. Fronts extend not only in the horizontal direction, but in the vertical as well. Therefore, when referring to the frontal surface (or frontal zone), we referring to both the horizontal and vertical components of the front.

There are two main types of front:

Cold Front

Warm Front