Describe the atmospheric conditions at the surface and aloft that are necessary for the development of most supercell thunderstorms. (Include in your answer the role that the low-level jet plays in the rotating updraft.)
What will be the ideal response?
ANSWER: Supercell thunderstorms are long-lasting violent thunderstorms, with a single rotating updraft that forms in a region of strong vertical wind shear. A rotating supercell is more likely to develop when (a) the winds aloft are strong and change direction from southerly at the surface to more westerly aloft and (b) a low-level jet exists just above the earth’s surface.
If the winds aloft are strong (strong shear) and change direction with height (from more southerly at the surface to more westerly aloft), the storm may move along in such a way that the outflow of cold air from the downdraft never undercuts the updraft. The wind shear may be strong enough to create horizontal spin, which when tilted into the updraft causes it to rotate. In this situation, the thunderstorm may grow into a larger, long-lasting (longer than an hour) severe storm called a supercell that has a violent updraft and a single cell.
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