West Bay & Chesil Beach
The northeast section of Lyme Bay, around West Bay and east along Chesil Beach often appears to enjoy its own mini weather system (micro climate). While the majority of Cornwall, Devon, Somerset and Dorset might be experiencing cloud and / or rain, West Bay will often be bathed in blue sky and sunshine. Why is this? We need to delve into some basics of cloud formation.
Air generally contains invisible moisture or water vapour. Clouds form when air rises through expansion which then cools, causing some of the water vapour molecules to condense on small particles of dust in the atmosphere (as saturation of the air is approached), consisting of droplets of water or ice crystals.
Air rises for three main reasons:
- Sunshine – Heat from the sun or warm ground warms the air and makes it lighter, causing it to rise into the sky.
- Terrain – Air rises as it is forced upwards due to changes in the terrain. This often occurs when wind blows air over mountains or cliffs from the sea.
- Weather Front – At a cold front, cold air is pushed under warm air, forcing it upwards. At a warm front, warm moist air is forced up and over the cold air.
Along the coast eastwards from Land's End, cliffs line the coast and present the conditions for any rain to fall. After passing over the peninsular of South Devon, the air falls again to pass over the waters of Lyme Bay, causing the opposite condition to that of forming clouds. This air is now less moist but also capable of holding more moisture. So the air's water droplet or ice crystal state turns back into water vapour. The clouds therefore fade away. When the air arrives at West Bay, the cliffs cease. There is then almost 18 miles of beach with a gently rising terrain behind, causing air to rise slowly onto the land. By the time sufficient moist air has risen to form clouds again, this air has also travelled a few kilometres inland.
Abbotsbury Subtropical Gardens about halfway along the Chesil Beach benefits from this effect, while the Meteorological Office regularly overlooks this in its weather predictions for the area.
The above conditions are generally satisfied when our weather arrives from the southwest, which for the United Kingdom is most of the time. However, under more severe conditions or when our weather arrives from a different direction, then even West Bay can get rain!