Fascinating Meteorology Terms: Mackerel Sky and Mare’s Tails

Altocumulous clouds forming a mackerel sky (first photo) and swift cirrus clouds resembling mares tails (second photo)

Another beautiful sight for the eyes, Mackerel Skies and Mares Tails are cloud formations that have distinctive patterns and displays of beauty in our atmosphere. These cloud formations are rather common and can hint at inclement weather as they are often seen during specific weather patterns. So, if you see these beautiful cloud formations you will be aware of the weather that is expected to precede. 
Characterized by rows of clouds arranged in a pattern of ripples or waves often resembling fish scales, a mackerel sky is quite a crowd pleaser of beautiful sky displays. This type of cloud formation is created by two different types of cloud formations: altocumulus and cirrocumulus clouds. Altocumulus are mid level clouds that are made up of mostly water droplets that form at elevations around 2000 meters to 7000 meters. These clouds are puffy and can be dense at times, blocking out most of the sunlight making the day look almost overcast. Cirrocumulus clouds are higher level clouds. They are mostly made up of ice crystals and take the form of small puffy white tufts. These are not likely to block out most of the sun like altocumulus can. They are rather thin in nature and more scattered. 

Although these clouds are fair weather clouds, meaning they are often seen during times of calm weather, these clouds most often prelude to unsettled weather. Altocumulus and cirrocumulus clouds are usually an indication of rising air and are seen ahead of a warm front. When warm air rises you can expect moisture to condense into rain. Most of the time when altocumulus clouds are spotted in the morning during a humid summer, pop-up thunderstorms can be expected by late afternoon that same day.    

Mares tails are characterized by clouds that are long, thin and wispy. They are called mares tails because they resemble the long flowing tails of horses. Cirrus clouds form like this.They are thin, high-level clouds solely made up of ice crystals. They are so high in the atmosphere they are influenced by strong upper level winds called prevailing winds that flow in a specific direction depending on the region. You can also spot these clouds on a clear fair weather day out ahead of a warm front.

Sailors used to use clouds as weather predictors during their trips across seas when technology and weather predictions were not as advanced as they are today. Whenever a combination of mackerel skies and mares tails was spotted, it meant that the weather was deteriorating and a low pressure system was on its way. This was typical of these clouds, being ahead of a warm front meant a cold front was to follow. Both warm and cold fronts are associated with low pressure systems that can produce wind, heavy rain and unsettled seas.

© 2020 Meteorologist Alex Maynard

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Sources:
Ahrens, C. Donald., and Robert Henson. Meteorology Today: an Introduction to Weather, Climate, and the Environment. Cengage, 2019.
“Cirrocumulus Clouds.” Met Office, www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/high-clouds/cirrocumulus.
“Clouds Form Due to Weather Fronts.” UCAR Center for Science Education, scied.ucar.edu/cloud-form-weather-fronts.
“Weather Lore That's A Bit Fishy.” Farmers' Almanac, 5 Jan. 2020, www.farmersalmanac.com/what-is-a-mackerel-sky-26275.