Weather Maps

A surface weather map shows the position and movement of weather systems.

It may show:

• areas of high and low pressure;
• isobars;
• warm and cold fronts;
• ridges; and
• troughs.

In New Zealand, weather systems generally move from west to east.

Isobars

Isobars are lines on a weather map connecting points of equal atmospheric pressure.

The spacing of the isobars gives an indication of wind strength.

Isobars spaced far apart:

• weak pressure gradient;
• generally lighter winds.

Isobars spaced close together:

• strong pressure gradient;
• generally stronger winds.

Remember:

Tightly packed isobars = strong winds.

Anticyclone – High

An anticyclone, or high, is an area of high atmospheric pressure.

In the Southern Hemisphere, winds circulate anticlockwise and outwards around a high.

• Air generally sinks.
• Pressure is highest towards the centre.
• Winds generally flow outwards.
• Highs tend to be large and slow-moving.
• They are generally associated with widespread, longer-term settled weather and lighter winds.

On a weather map, a high-pressure system is identified by an H.

Depression – Low

A depression, or low, is an area of low atmospheric pressure.