WEATHER LORE CLOUDS : SHEETS AND HEAPS

The mood of the weather is clearly seen in the face of the sky. The ever changing patterns and colours painted across the sky by clouds is one of the wonders of the ‘weather world’.

But, what are clouds and how do they form? Air must be made to rise for any cloud to form. The upward motion takes the air into higher areas where lower pressure causes the air to cool. If the air is cooled to its ‘dew point’ condensation begins and water vapour, (an invisible gas), forms the tiny condensation droplets or ice crystals we see as cloud.

The World Meteorological Organisation recognises 10 different types of clouds. But, really, I think we can reduce this to just two main sorts.

Sheets’ and ‘Heaps’. Yes, most clouds are a variety or combination of these two simple forms.

Sheet, or to give them their proper name ‘stratus’, clouds are layered clouds which show as a white or grey overcast sky. They vary in height and thickness and are usually produced when air rises slowly over hills or at a front.

Heaped or ‘cumulus’ clouds are those fluffy, blobby, billowing ones that can be mistaken for a misshapen cauliflower. They vary from little white fluffs seen on a pleasant summer’s day….

… ....to deep, dark, towering ‘cumulonimbus’ cloud.

Formed when the heat of the sun on the ground causes bubbles or ‘thermals’ of air to rise, these danger clouds bring us some of our most violent and spectacular weather.

Not to be trusted, these cumulus clouds confirm the old weather lore: “ A dappled sky, like a painted woman, soon changes its face.”