What weather patterns result in droughts?

Strangely, weather scientists can’t explain why droughts occur in some years, or decades, and not others. They do come in cycles. Droughts occur when a high-pressure area settles over a region and then doesn’t move on, as is usual. Clouds can’t form because the high pressure is pushing down the air, causing “compressional warming” and lowering the humidity. Essentially, the conditions needed for creating rain have been removed. When this goes on for a long time, a drought occurs. Although the 20th century had some notorious droughts, one of the most famous of which produced the Dust Bowl of the 1930s, the United States and other parts of the world have seen worse. There were “mega-droughts” in the 13th and 16th centuries, and there’s nothing to stop such droughts from occurring again.