The Weather

Atmospheric pressure on maps is measured at sea level The Isobars Those plain lines that curve across the map are called isobars (iso = equal, bar = pressure). They join together places of equal atmospheric pressure. Some have numbers on them showing this value in hectoPascals. Atmospheric pressure on maps is measured at sea level

Winds blow almost directly along the isobars. ANTI-CLOCKWISE around HIGHS.     CLOCKWISE around LOWS

The closer the isobars, the stronger the winds.

When a high is over us we can expect dry sunny weather The Highs When isobars enclose an area of high pressure (above 1013 millibars. This is called a High, anticyclone or Ridge and its centre is labelled on a weather map by an 'H'. When a high is over us we can expect dry sunny weather

When a low is over us we can expect, cold rainy weather. The Lows Isobars make shapes and patterns. When they enclose an area of low pressure this is called a Low, cyclone, trough or depression and its centre is labelled on a weather map with an 'L'. When a low is over us we can expect, cold rainy weather.

What to do when trying to predict the weather. Look if any anticyclones or cyclones are present. Wind direction Wind speed Fronts Especially in the South Island think of the southern Alps

Write down the important features to look out for on this map to forecast Gisborne’s weather? Write a weather forecast for Gisborne telling us the wind direction/strength and the expected weather

Weather forecast for Gisborne Sunday Max: 18°C Min: 14°C Rain, heavy at times. Gusty south easterlies

Analysis Map v’s a Prognosis Map You can generally get two different types of weather maps. An analysis map What has actually occurred. The current situation Prognosis What the future holds for us

Fronts, Troughs and Convergence Zones A front marks the boundary between two air-masses, and appears on the weather map as a line with triangles or semicircles attached.

Cold Front Cold fronts push in underneath the warmer air ahead of them, forcing the warm air upwards and making cloud and areas of rain. As a cold front passes by: any rain clears but showers may appear, humidity drops, air temperature usually drops, pressure rises and the wind changes direction.

Warm Front The advancing warm air rises over a zone of retreating cooler air, making a cloud bank that slopes forwards from ground level upwards, often bringing prolonged steady rain. As a warm front passes by: any rain becomes patchy but humidity remains high, air temperature may rise a little, pressure steadies, and the wind changes direction.

Occluded front Occurs when a cold front overtakes a warm front, so that all that remains of the original warm air is trapped above, where it cools making dense cloud and rain. As an occluded front passes by: any rain becomes patchy, wind eases, the rate of pressure fall may level out but air temperature does not change much.

Stationary front A front which has lost its impetus for movement, so that neither air-mass is making much progress. It takes a while for a stationary front to pass by: any rain clears only slowly and temperature and pressure do not change much.

Weather from around the world Weather in Darfield www.metservice.co.nz/default/index.php?alias=farmcanterburyplains Weather from around the world http://www.bbc.co.uk/weather/world/