An observation over 21 years living in Paignton.
Holiday main seasons down comes the rain. It can be dry for weeks on end and as soon as the motorists arrive in their drives the rain arrives. Now it could be a coincidence but it happens too often IMO.
So what changes have occurred that might be responsible for causing it to rain?
1. Sometimes along our particular part of the coast we are privileged to be visited by some unusual clouds rolling along the coastline. They do not cross over the hot dry coastline beyond the black tarmac road. So one side is shrouded in mist, the other side is a bright sunshine day with clear air. This can last for many hours as the mist rolls around like washing in a tumble dryer and is channelled along the coast.
2. Where the trees meet the sea mist rolls inland and hugs the wooded areas but goes no further than the tree line does. Walking in the trees on these particular days the temperature is several degrees below that outside of the trees and the air is saturated with water, the trees are dripping and the ground is moistened.
3. When the mist finally vanishes it remains shrouding the trees and the trees milk the remaining water from the air over several hours more
4. Thermals rising from the hot tarmac road can be seen as you drive along it. You can see the wavy thermal pattern as the heat rises. These thermals rise high into the atmosphere and form an invisible barrier against ocean born humidity. These same thermals cause the same barrier along desert coastlines and are undoubtedly responsible for the inherent lack of rainfall in these areas.
5. Trees transpire vast amounts of water into the atmosphere and in doing so remove the thermal barrier that prevents cloud and mist from crossing onto the land. They lower the temperature and as warm moist air rises it is cooled causing a downdraught which causes warm air to rise in a density flow and indeed this can be seen happening at times when dew point has been reached.
6. The holiday traffic involves a massive increase in vehicles cruising along the hot roads. These obviously provide some shadow and while they are moving along they remain cooled by the moistened air flowing over them from the exhaust emissions of other vehicles so an overall reduction in temperatures due to traffic is offset against the heat generated by the engine and the friction from the transmission, brakes and tyres.
7. The exhaust emissions contain collectively a vast amount of warm water released into the atmosphere along with particles which rise due to the heat from combustion. These gasses quickly cool transferring the heat into the atmosphere and fall back towards the ground while the dry hot air rises again generating the same flow and return system that the trees perform.
8. This additional water from exhausts also blocks out some of the suns energy and like the trees removes the thermal barrier so moisture from the ocean can again cross onto the land and fall as rain, and rain it does with incredible regularity.
So the old adage said to holiday makers with regularity “you have brought the bad weather with you may have a lot of truth in it after all.