What do clouds tell me?
Clouds are the most visible indicators of weather and impending changes. Take a small weather reference text with you on trips and learn to identify different cloud types and become familiar with their movement. There are three main cloud levels: high, mid and low. In southern Australia, high-level clouds, such as cirrus or altocumulus, moving in from the west may indicate an approaching frontal system that could arrive in the next 12 to 36 hours. In tropical areas, such clouds may mean a quicker change for the worse.
A high flying plane leaving long-lasting contrails in the air indicates relatively high levels of moisture, also a forewarning of potential bad weather coming from the west.
Fluffy cotton-ball cumulus clouds may appear during sunny afternoons, as the warming earth heats the air which rises. Depending on moisture content, these fair weather clouds will appear. If the air is humid, it becomes unstable. The heat released by condensation drives the air to greater heights, producing more condensation. This feedback process continues and large cumulonimbus thunderheads develop, extending from low to very high levels. Watching this process can be exhilarating. The wise leader, noting this process, will try to get his or her party away from exposed locations. Chaotic winds within thunder clouds generate static electricity that discharges as lightning. In the tropical north, this procedure can be repeated day after day in hot, moist conditions.
You can roughly estimate how far away the storms are, by counting the seconds between a lightning flash and the following thunder. Noise from thunder travels about 1 km in about 3 seconds. Use these distance estimates to plan your party’s next movements. Move off the tops of ridge lines and exposed slopes. Be prepared for sudden rain squalls and potential hailstorms. A green tinge to the base of a cloud or a whitening of rain may indicate approaching hail or snow.
Another indicator is the colour of the sky: ‘A red sky at night is a shepherd’s delight; a red sky in the morning is a shepherd’s warning’. If it has been a cloudy, miserable day and just as the tents are being erected, the rain stops and the sky turns red, this indicates a break in the cloud to the west, and higher air pressure, probably associated with improving weather. If, however, a morning sky is deep red, it may mean rain or a cloud-filled sky for most of the day.
While pitching a tent next to a dry creek bed or a small meandering stream and watching the thunderheads and lightning play about the distant hills, you should consider the impact the of mountains on precipitation, and may reassess the location of your camp as thoughts of flash floods occur.
Coronas or haloes about the moon indicate the presence of mid- to high-level clouds and are often a sign of advancing rain or storms. The larger the halo, the higher the cloud, and so the further off the worsening weather.
Care must be taken when venturing into the forests of southern Australia in summer. Forest fires can cause much damage. The alert leader will look out for pyro-cumulus clouds. A bush fire will generate heat, causing air to rise in a column of smoke. With sufficient heat, the smoke column will rise to the condensation layer leading to the formation of dense white cumulus cloud. After a thunderstorm, a party in the bush should be wary of fires ignited by lightning.