Air masses and weather maps

The main features of a typical weather map, such as the one shown here, are:

• regions of high and low pressure, delineated by a pattern of isobars. The isobars are generally drawn at intervals of 2 or 4 hectopascals, depending on the scale of the map.
  
  
• cold and warm fronts that delineate major boundaries between air masses. These are shown as a bold line with either triangles for cold fronts or semi-circles for warm fronts along it.
  
  
• troughs of low pressure, shown as dashed lines
  
  
• areas where rain has fallen in the past 12 or 24 hours, shown by hatching
  
  
• surface wind direction and speed at spot locations. The direction from which the wind is blowing is designated by an arrow shaft and the speed by barbs along the shaft. (A long barb designates a speed of approximately 20 km/h. A combination of 2 long and 1 short barbs would designate 50 km/h.)
  
  
• in some cases weather maps are overlaid on satellite images whereby cloud bands associated with fronts and low pressure systems are often readily identifiable.

The term 'synoptic chart' is often used as an alternative to 'weather map'.

See also 'Interactive Weather Map' (Flash 4 enabled web browser required)