Wind Arrows

Wind direction is shown by the direction in which the arrow is pointing. The strength is indicated by the size of the arrow. The larger the arrow, the stronger the wind.

On both website and television forecasts, once the speed of the wind reaches a certain strength, the wind arrows will not increase in size. On the website, this speed is 35mph on television, this speed is 45mph. The small arrows that would indicate light winds at speeds below 7mph are omitted from charts shown on the website.

The data files supplied by the Met Office contain a number of fields for each arrow. Apart from direction and a value of size, each arrow is given a temperature value. We can use the temperature to colour arrows so that cold air will be seen as blue arrows and warmer air in white and yellow.

The wind forecast is tied to grid points on the surface of the Earth. The wind forecast for a particular location can be seen to change as the direction, size and colour of the arrow changes.

On television broadcasts, the wind forecast is animated and pressure systems can be seen to move across countries and regions. On the website, still charts are used to give the forecast for a particular time.

The wind arrow graphics are closely related to pressure charts, in that as the isobars on the latter become more tightly packed, so then the wind will strengthen - this being depicted by the larger arrows.

It is worth noting that the wind direction is approximately in line with isobars (if you stand with your back to the wind in the northern hemisphere, you will have low pressure on your left hand side and high pressure on your right hand side).

It is an interesting exercise to overlay a wind chart for a particular area over a pressure chart for the same time and area, to see the relationship between the two weather tools.