Rain (or snow) will fall:
Within five minutes after the arch of the thundercloud is seen to move toward one.
Within five minutes when the curtain of falling drops obscures the landscape to the west of one.
Within a few minutes after the bottoms of cumulus clouds turn from black to gray, letting down visible trailing showers.
Within a short while after the winter sky has become uniform in color.
Within an hour after the pavement-like, but scarcely discernible, thundercloud consolidates along the west, if the wind is from the southwest. If the wind is from the southeast this cloud may take four hours to rise.
From two to eight hours after the sun or moon has vanished behind the cirro-stratus.
From eight to forty-eight hours after the first cirrus is seen, depending upon the distance from the sea and the time of year.
Every little while from southwest showers in the passing of a summer low.