Features September 2016 Issue
Reading the Sky
You don’t need a meteorology degree to read the sky, but if you have a basic understanding of what you’re reading, it can be an interesting story indeed.
A cloud is the visible manifestation of liquid water droplets or ice. It forms when humid air cools sufficiently for water vapor to saturate and produce condensation—the dewpoint temperature. On a dry summer day in California, this temperature might be 20 degrees F, and the weather remains clear. On more humid summer days in California, the cloud formation temperature might be 50 degrees, producing morning clouds along mountain peaks. When air is chilled to the dewpoint, the humidity becomes 100 percent and from the texts we expect saturation to occur. But in real life this doesn’t always happen. If a given volume of air doesn’t contain condensation nuclei—microscopic bits of dust, pollen, etc.—the relative humidity may exceed 100 percent without producing clouds. But for the most part, this relationship between temperature and dewpoint is correct.