The weather effects on aviation

Except perhaps for local or very short flights, a pilot, before taking off, obtains a weather forecast giving him the weather conditions, which are expected along the route of his flight and at his destination. Because weather conditions affect aircraft in flight, to a considerable extent, special aviation forecasts are provided by meteorologists at weather offices all over the world.

The meteorologist, or forecaster, prepares a weather chart* which shows the current weather conditions over the whole country. The current weather chart is called a synoptic chart. This synoptic chart shows the areas of low pressure, the areas of high pressure, where precipitation is falling, and all other weather conditions across the country.

From this weather map**, the forecaster can advise pilots of the weather conditions they can expect to encounter during their flights. A high-pressure area, for instance usually means good weather while a low-pressure area usually involves one or more fronts producing clouds and precipitation over many hundreds of miles.

Pilots will pay particular attention to a low-pressure area, which lies en route, and the weather conditions associated with that low-pressure area. The associated cold or warm fronts could involve clouds, thunderstorm, snow, rain and turbulence. From his charts, the meteorologist can forecast where this weather will be at a certain time in the future, and with the help of these predictions, the pilot will decide which route to fly, what weather conditions to expect. If the forecast is very bad, for example, dense fog or poor visibility due to snow, the pilot may decide to postpone his flight.

A pilot needs to know the wind direction and speed. A headwind will delay the arrival of flights and is to be avoided if it is possible. A tailwind increases the ground speed and results in a reduction in fuel consumption. Winds vary with altitude, and also from one place to another, so information on winds is very important.

A pilot needs to know how the wind will affect his aircraft. He needs to know things about the wind: its direction and its speed. The wind direction is where it is blowing from and the wind speed is how fast the wind is blowing.

The words, used to describe how strong the wind is, are: calm, breeze, strong, gale (very strong), storm.

Calm means that there is no wind; storm means that the wind is very strong. A sudden increase in wind speed lasting only a few seconds is called a gust and the wind is described as gusting.

A squall is similar to a gust but lasts longer. Wind shear is the word used by ATC to warn pilots of a sudden change in wind direction or speed. Wind shear is a rapid change in wind speed or direction over a short distance horizontally or vertically. It can occur at any height, but is far more dangerous when encountered close the ground.

When wind shear is forecast or is reported by aircraft, ATC will warn other aircraft.

Jet stream is high level wind, which is very important for navigation because they blow very fast. They can blow faster than 200 knots.

Turbulence can be light, moderate and severe. In severe turbulence an aircraft can lose or gain a lot of height.

Clear air turbulence, or CAT, occurs at high altitudes away from clouds. It is normally associated with jet streams.

Information about significant changes in metconditions in the take-off or climb area is transmitted without delay, e.g. changes in surface wind direction and speed, visibility, RVR, air temperature, thunderstorm, moderate or severe turbulence, wind shear, hail, moderate or severe icing, severe line squall, freezing rain, sand storm, dust storm, blowing snow, tornado, waterspout.

* A map is a drawing of a part of the world showing ground features.

** A chart is a typeof map, which includes navigational information such as controlled airspace, airways, radionautical equipment, dangerous and restricted zones, frequencies, beacons and other information that is necessary for flight preparation and operating.

***Latitude – together with longitude, latitude can be used to give the position of any place on the Earth.

e.g. The latitude of Montreal airport is N 45 38.

****Longitude – used with latitude to give a place’s position anywhere in the world.

e.g. The longitude of Reykjavik is W 21 56.