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What would it take to break the massive drought of 2012? Before we can answer the question, we need to know what's causing it in the first place. Obviously, when more water is coming out of the ground than going into it, the soil is going to dry out. That can happen due to below-average precipitation, above-average temperatures, or most often, a combination of both.
And when you have an upper-atmospheric pattern like the one we have this year, you get both. A persistent zone of high pressure is leading to sinking air over a large part of the country, and that makes it difficult for rain-bearing clouds to form.
"Conventional wisdom has it that a tropical storm or hurricane moving inland can end a drought," says The Weather Channel senior meteorologist Stu Ostro. "However, the extent of rainfall would not nearly be enough, given the scope and severity of this drought and the fact that the heaviest rain even with the largest tropical cyclones typically falls within a relatively narrow swath."
"There's been a persistent, strong, dry ridge of high pressure aloft anchored over the west-central United States," Ostro says. "A switch to the opposite pattern – a persistent, strong, stormy trough (dip in the jet stream) during the cool time of year when there's less evaporation would make a significant dent in the drought, though the drought is so massive and severe that it’s going to be hard to end it across even nearly the whole area."