Weather altering charms have been outlawed by the International Confederation of Wizards since the early 1940s. The practice was fairly common before being banned, the usual purpose being to ensure crops had enough rain or didn’t flood or freeze. However, while effective in the short term, long term weather became increasingly unpredictable. For example, while stopping or slowing the rain in the winter may seem like a good idea during a particularly rainy season, it may cause flooding later in the year or several years later, depending on the frequency and intensity of the spells. Causing rain in the summer may induce a drought. While it is possible that the effects may be mild, the resulting backlash will certainly be greater than what it originally would have been. Ensuring sunny skies for an afternoon may only cause rainy skies for a week, but inducing rain weekly for years on end will have a much greater backlash.
The case that finally ended weather spells for good was the American Dust Bowl. While it was true that Muggle farmers used incorrect farming methods to prevent wind erosion, it was wizards who caused the droughts in the first place. Wizarding farmers in the area magically induced rains, sometimes up to weekly, to grow crops that would not generally grow on the American Prairie. The combined effect of the spells gradually built up to the first drought in 1934. Unfortunately, instead of letting the backlash run its course, wizards fought back with more weather charms, and were temporarily successful for the duration of 1935. The same thing happened in 1936, and again in 1939. Finally, in 1940, the Magical Congress of the United States of America (M.A.C.U.S.A) outlawed weather charms, and the droughts and dust storms finally died down. Shortly after, the International Confederation of Wizards outlawed weather charms in all wizarding nations.
Ms. Nyx Bluestone, July 22nd, 2015