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Mackerel sky

Photo credit: Denni Windrim

A mackerel sky is an indicator of moisture and instability at high levels. If the lower atmosphere is stable and no moist air moves in, the weather will most likely remain dry. However, moisture at lower levels combined with temperature instability can lead to spectacular thunderstorms should the rising moist air reach this layer. In weather lore, a mackerel sky portends changeable weather.