Field guide training: Climate and weather – Part 6

If you are a field guide in the wilderness, it is of vital importance to be able to interpret weather phenomena correctly. Especially rainfalls and thunderstorms play an important role because they can become dangerous on a safari tour. Clouds and their shapes often reveal the weather conditions to be expected. A basic knowledge about the so-called nephology (cloud science) should not be missing in any guide training.

Clouds are created by the evaporation of water from oceans, lakes, rivers or moors. The evaporated water molecules rise into the atmosphere, where they condense again to water drops due to the air pressure and the rather low temperatures. The temperature at which the air has reached its maximum water holding capacity is called dew point.

The resulting water drops accumulate on small particles in the atmospheric air, also called nuclei. These are usually dust, soot or salt crystals. The combination of air particles and water drops finally joins together to form the actual cloud. If the weight of the water becomes too heavy, it falls back to the earth as rain.

Different types are distinguished with regard to the cloud shape:

1. Cumulus clouds are located in rather low atmospheric layers up to 3000 meters altitude. They are usually as high as they are wide. Their bottom side is often flat and the top rugged. Because of their cotton wool-like shape, they are also called "fluffy clouds". As long as they don't get too big, they often occur during periods of good weather.

2. Stratus clouds occur in lower atmospheric layers, but are much denser than cumulus clouds. In addition, they often form a closed cloud-cover, why they are called also high fog. However, in contrast to fog, they often produce drizzle or snow.

3. Cirrus clouds occur at altitudes of up to 10,000 meters. These are delicate, thin veil clouds, which consist mainly of ice. They only move slowly in the sky and hardly interfere with sunlight or moonlight. The curvature of the Cirrus clouds often indicates the direction from which a weather change can be expected within the next 24 hours. These are often warm fronts that can transport thunderstorms.

4. Nimbus clouds are often divided into the two types Nimbostratus and Cumulonimbus. Nimbostratus clouds are usually associated with a low pressure area at the lower edge of the troposphere. They are characterised by a dense, dark grey layer in the sky and often bring rain or snow at higher altitudes. Cumulonimbus are the classic storm clouds that bring rain, storm, lightning and thunder. Their extent often reaches deep into the stratosphere. Sometimes, high winds flatten the upper part of the clouds, creating an anvil shape. The tip of the anvil points in the direction in which the storm moves.

As a field guide you should be particularly careful of thunderstorms, as they represent one of the greatest dangers in the bush. They occur when very humid, warm air masses meet cold air layers. This leads to a strong condensation of atmospheric humidity and the formation of cumulonimbus clouds typical of thunderstorms. These are characterized by their vertical orientation and strong up winds. The energy transported by the clouds is often discharged by lightning. The thunder that follows is generated by the suddenly expanding air around the flash.

If you are surprised by a thunderstorm out in the field, you should stay away from tall objects such as trees or masts, as lightning always strikes the highest point of the landscape. Instead, you should seek protection in a metal car, as this works like a Faraday cage and directs the flash directly into the ground. If no car is available, it is important to make yourself as small as possible. The best place to do this is in a hollow in the ground, where you squat down and wait until the thunderstorm has passed.