Red Sky in the Morning. . .

"Red sky in the morning, sailors take warning".



This is a little piece of weather lore that actually works, in our mid latitudes, North American context.  Generally our weather systems move roughly west to east, so we see a rising sun in the east in clear skies, with light coming in at a low angle, so having to pass through a lot of atmosphere to reach us.  Having to come through so much air, the shorter wavelengths of light are scattered out and longer wavelength red is the predominant colour of the spectrum to reach us.  Hence red sunrises and sunsets.

Now a moisture laden sky gives more stuff for this red light to bounce off.  So coming from a clear sky in the east into moisture laden sky coming from the west, we get the "red sky in the morning".  So we can look for some damp weather today, as a low pressure system moves in from the west, bringing some rain, or at least a good chance of rain with it.