Being able to forecast mountain weather is a crucial skill when travelling or living in mountainous terrain. Checking online weather forecasts before leaving shelter and carrying a portable radio on longer treks is always a good idea. Nevertheless, it is crucial to pay attention to clouds and rapid changes in air pressure while on the trail. Such changes can alert one to changing weather conditions in the field. Clouds offer the most accessible reading of weather changes since they are formed by atmospheric changes.
What brings clouds?
The warmer the air is, the more water vapour it can hold. Clouds are usually produced through condensation – as the air rises, it will cool. Reducing the temperature of the air, decreases its ability to hold water vapour so that condensation occurs. The height at which dew point is reached and clouds form is called the condensation level.
Types of clouds
Broadly speaking, there are three categories of clouds. These are cirrus, stratus and cumulus. These broad categories can combine in various permutations and combinations to form hybrid clouds.
- Cirrus clouds are high level clouds and they look like thin, wispy strands. The name cirrus comes from the Latin word meaning a ringlet or curling lock of hair.
- Cumulo means “heap” or “pile” in Latin. Cumulus clouds are often described as “puffy”, “cotton-like” or “fluffy” in appearance, and have flat bases. They are low level clouds, often found below 2000 metres.
- Stratus is used to describe flat, hazy, featureless clouds of low altitude varying in colour from dark grey to nearly white. The word “stratus” comes from the Latin prefix “strato-“, meaning “layer”. Stratus clouds mean rain if it is warm and snow if it is cold. They look like a huge grey blanket that hangs low in the sky.
But, if these classifications confuse you, remember this simple rule of thumb
Cirrus Clouds indicate a change in weather
High, wispy cirrus clouds are often a signal of changing weather. When these wispy clouds meld together, they create a “milky” sky. Any time this milky sky is accompanied with strong winds, it is a clear indication that a storm is headed towards you.
Dark many headed Cumulus clouds spell trouble
Cumulus clouds indicate fair weather when they are white and widely separated, but if they are dark, large and many headed, they are capable of bringing heavy rain. The likelihood of cumulus clouds developing into rain bearing clouds increases as the atmosphere warms up in the summer. This occurs especially in the afternoon (between 1300 – 1800 hours). This is why we urge trekkers to start early and stay off high ridges or mountain passes after 1200 hours.
UFO like clouds on mountain tops
Lenticular clouds or lens-shaped clouds hovering over a mountain peak, indicate strengthening winds and the approach of moisture-laden air. Both indicate a storm from 6 to 18 hours away.
Ring around the Sun or Moon
A ring around the sun or moon indicates condensing moisture. This is often a sign of cirrostratus clouds. A Cirrostratus cloud cover accompanied with a darkening sky is a sign of rain or snow, within 72 hours.
Himalayan weather is often difficult to predict. Yet, clouds are the best indicators of local Himalayan weather patterns and observing changing cloud patterns is the key to avoid being caught in an unexpected storm. Be sure you are always thinking about a contingency plan, your descent options, and the commitment factor while you are trekking. Going to the Himalayas prepared for any and all conditions and with an appropriate level of knowledge and decision-making ability for your objective, is the most effective way to limit risks while trekking.