Weather Prediction from Observations of Cloudlets

Abstract

MAY I refer to the first letter of Sir G. Archdall Reid? (NATURE, November 7, p. 676). He says: “if then the behaviour of the smallest and thinnest fragment of cloud that can be clearly isolated be watched, it is usually possible to predict very quickly and with fair confidence the state of the weather for the next few hours. If the cloudlet waxes visibly, rain is almost certain; if it wanes, fine weather is equally probable; if it neither waxes nor wanes, existing conditions are likely to continue.” It seems to me that the method of forecasting is falsified on every day on which clouds form and when rain does not follow, and there are very many such days in the year; for the cumulus of a fine day, which is common in spring, summer, and autumn, and occurs sometimes in winter, begins its life as a cloudlet, whether the ordinary man gets up early enough to see it or not. Certainly, too, cirro-cumulus often begins its life as cloudlets, but I have never seen cumuli “wane into cirro-cumuli” and rather doubt whether any one has ever observed such a phenomenon.