The thunderstorm complex Tuesday morning brought heavy rainfall to Eastern Iowa and some very strange looking clouds to major urban centers like Cedar Rapids. The featured image and many others were captured by many people with many questions about how clouds like that form. They are a result of a very strong and stable boundry between humid air and drier air. The cloud's border sort of floats along this interface and appears to be very sharp due to the near zero entrainment of dry air which would produce a "fuzzy" look.

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