photo #5941983

So says the rhyme of the ancient mariner: ‘Red sky at morning, sailors take warning.’ The idea is that a red sunrise can act as an early indicator of unsettled weather to come. There is some truth to this old saying. A red sunrise happens when the sky off to the east is free from cloud, letting the morning sunlight shine onto clouds overhead. This happens when there is high pressure to the east. High pressure also tends to trap tiny airborne particles in the lower sky, which has the effect of making a sunrise look redder. In middle latitudes, prevailing winds and jet streams mostly drive weather systems from west to east, and so a red sky in the morning suggests the high pressure is moving east, and a low-pressure system is approaching from the west. Low pressure can bring the stormy weather sailors fear. Rich Dow (Member 50,373) spotted these crimson Altocumulus at sunrise over Sonoma County, California, US. The red skies did indeed herald a day of heavy rain and strong winds. The streaks of cloud hanging from the Altocumulus and catching the morning light are known as virga. They’re trails of precipitation that are evaporating before reaching the ground. Seems this red sky is going out of its way to warn sailors of the coming downpours.