Predicting Weather: How clouds affect light quality.
Good clouds can make or break a landscape photograph. Understanding the weather is an important, if unsung, skill for a landscape photographer. What the weather is doing (or is about to do) will make a difference to the quality of the light on the landscape. And it's the quality of the light that will make a difference to the success or otherwise of a shot.
The light from the sun shining high in a cloudless sky is very hard. This results in sharply-defined and dense shadows. This is fine for very graphic compositions (when hard shadows are used to define shape) but it's not very subtle. Clouds act as natural reflectors, softening and filling in shadows. At either end of the day clouds also bounce the warm light of the sun back down on to the landscape in a very pleasing way. It's probably fair to say that clouds are a landscape photographer's best friend.
The distinctive mackerel appearance of Cirrocumulus.
Well, sometimes. You can have too much of a good thing. A blanket covering of cloud blocks out the sun, reducing contrast and producing a very flat light. For wide-open vistas this isn't ideal. In low contrast the texture of the landscape is more difficult to discern and the resulting photos can look dull and uninteresting. However, overcast days are ideal for woodland, which benefit enormously from the reduction in contrast. Overcast cloud is known as Stratus cloud. It's essentially fog that's not at ground level (or to look at it another way, fog is Stratus cloud that's reached ground level).
A change from good to bad weather shouldn't necessarily be a deterrent. I enjoy shooting in those in-between periods.
Clouds can also be used to predict the weather. High Cirrus clouds generally mean a change in the weather, often for the worst. The most familiar type of Cirrus cloud is Cirrocumulus, also known as mackerel cloud because of its resemblance to the patterns formed by a school of mackerel. An old folk saying 'mackerel sky, a storm is nigh' has a good basis in fact.
Cumulonimbus clouds have a top-heavy appearance and mean rain and even lightning is on their way.
However, the fact that the weather is set to change isn't necessarily a bad thing. Often the most dramatic light occurs at the cusp of the change, when good weather turns bad or vice versa. Cirrus clouds that have a streaked appearance are useful indicators of wind direction. Once you know that, you'll know the direction the change of weather is coming from.
Low and brooding, Nimbostratus means heavy rain.
Another familiar type of cloud are Cumulus clouds. These are low clouds that have a flat base and a puffy, cauliflower appearance to the stack above. Cumulus are fair weather clouds. If rain does fall it's likely to be in the form of a short-lived shower. However, if the stack grows upwards and develops into a Cumulonimbus cloud then heavier rain and lightning will result.
Nimbostratus cloud is low, thick and wet looking. Unsurprisingly this means that rain is very, very likely. And long lasting. Unless you're particularly keen to shoot in the rain, the appearance of Nimbostratus is a sign that it's time to go home and make a start on processing all the dramatic landscape photos you've shot previously.