Red Sky at Night
When the sun sets in the west, the light hits the atmosphere at a different angle. If an area of high pressure is in the west, skies will be clear, the dense cool air will sink and higher concentrations of dust will be at lower levels.
The dust acts as a filter and limits short wavelength light (violets and blues), but will allow for long wavelengths (reds and oranges).
If the sunrise is red, it means that the area of higher pressure has moved through the area and could be followed by a low pressure system.
