Clouds lowering and thickening, ceiling lowers. Puffy clouds begin to develop vertically and darken.
Sky is dark and threatening to the West.
Clouds increasing in numbers, moving rapidly across the sky. Barometer falling steadily or rapidly. Wind shifting North to East and possibly through East to South. If on land, leaves that grow according to prevailing winds turn over and show their backs. Temperatures far above or below normal for the time of year.