Virtual Skies

Weather Chart

Take Control Activity

An understanding of weather concepts is critical in aviation. Safety in flight is subject to conditions of limited visibility, turbulence, wind, and precipitation imposed by the weather. Weather also must be accounted for in navigation. In this exercise, we will examine some of the major meteorological factors critical to aviation, and how these factors are commonly depicted.

Wind is a vital consideration in navigation. It can assist or hinder the speed of an aircraft relative to the ground, and can blow an aircraft from its intended course. The movement of air may become turbulent and under extreme conditions, turbulence can pose a danger to aircraft. Weather charts use wind arrows to depict the speed and direction of wind. The head of the arrow points in the direction toward which the wind is blowing. (However, winds are described by the direction from which they are blowing - a north wind is a wind blowing from the north.) Wind speed is indicated by the feathers on the arrow. Full feathers represent 10 knot increments; half feathers represent five knots.
Wind arrow diagramWind blowing from the southwest (225 degrees) at 25 knots.
Wind arrow diagramWind blowing from the east (90 degrees) at 10 knots.

Atmospheric Pressure
Differences in atmospheric pressure from one area to another result in wind. Atmospheric pressure can also affect aircraft performance; under low pressure the air is less dense, and aircraft are not as efficient at taking-off and climbing. Changes in pressure can herald changes in weather; a sudden drop in pressure may indicate the approach of a storm. Atmospheric pressure is typically expressed in millibars. Normal pressure at sea level is 1013.2 millibars. Weather charts usually depict atmospheric pressure using isobars - lines connecting areas with equal pressure.

Diagram showing isobars

Cloud Cover
Clouds can have a dramatic effect on visibility. This is especially critical for VFR (Visual Flight Rules) flights which depend on the ability to see and be seen. Precipitation, which may be associated with clouds, can further impact visibility. Clouds can pose additional dangers. For example, aircraft flying into cumulonimbus clouds may encounter extreme turbulence and violent updrafts and downdrafts that can literally tear a plane apart as well as lightning, icing, and other hazards. A variety of weather charts depict a wide range of information about cloud cover. On surface weather maps, the following symbols are combined with the heads of the wind arrows to depict the amount of cloud cover.

Clear weather symbol

Scattered clouds symbol

Broken clouds symbol

Overcast with breaks symbol
Overcast with Breaks

Overcast symbol

In the following exercise, interpret the information on the simplified surface weather map in order to match the verbal weather descriptions with the stations shown on the map.

Weather Map

Wind 220 degrees at 20 knots. Pressure 996. Overcast.

Wind 45 degrees at 10 knots. Pressure 1017. Clear.

Wind 225 degrees at 25 knots. Pressure 1011. Scattered clouds.

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