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A thick layer of stratocumulus clouds is observed in a winter day in northern Europe where the temperature is close to 0°C at ground level. What can you expect?
  • A
    A high probability for icing in clouds. Severe icing in the upper part due to accumulation of large droplets.
  • B
    Turbulence due to a strong inversion, but no icing because clouds consist of ice crystals.
  • C
    Decreasing visibility due to snowfall below cloud base, but only light icing in clouds.
  • D
    Reduced visibility and light icing in clouds.

ICING. Some of the factors affecting the severity and the type of icing that occurs:

  • Size of supercooled water droplets. The larger the supercooled water droplets, the greater the intensity of icing. Large supercooled water droplets can be found:

    • Freezing Rain FZRA

    • CU and CBs

    • NS

  • Concentration of water droplets. The higher the concentration, the greater the intensity of icing. Concentration is highest in convective clouds – CU and CB - and NS.
  • Air temperature. Dictated what size of super-cooled water droplets will be present in a given cloud and also in what quantity.

In this case, it is true that Stratocumulus clouds primarily contain small sized water droplets. However, bear in mind that temperature is very important. Temperatures at the surface are quite cold in this case (close to 0 °C). The cloud top will typically exhibit the coldest temperatures in these clouds. When the temperature is just right, these harmless-looking clouds can surprise a pilot with some moderate or even severe icing while climbing or descending through them – especially at the top of the cloud where the concentration of super-cooled water droplets will be higher. The higher the concentration of super-cooled water droplets, the greater the intensity of icing. Even though it's more common to observe light/moderate icing conditions in SC clouds, in extreme conditions, as the one depicted in the question, severe icing may occur.

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