When windows won't open and salt clogs the shaker/Weather will favor the umbrella maker is another weather-predicting rhyme. When the air is humid, or full of water vapor, wood swells. It absorbs the water in the air. Salt also absorbs water in the surrounding air, forming large lumps. Wood-framed windows and salt in shakers become difficult to use. As the humid air reaches its saturation point, rain (and umbrellas) are likely to be seen.