Marine-Influenced Snowfall (MIS)

Lake-effect snow is a type of precipitation that occurs when relatively warm lake or sea surfaces destabilize cold polar air masses as they pass over them, leading to the acquisition of heat and moisture. During this process, the cold air mass warms and gains moisture from below as it moves over the water, creating atmospheric instability. As a result, cumulus-type clouds form and produce snowfall. This type of precipitation typically affects narrow areas and can lead to rapid accumulation of heavy snow.

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The formation process of lake-effect snow occurs in the following stages:

• Cold Air Flow: A cold air mass moving from the north warms and gains moisture as it passes over the surface of a lake or sea.
• Instability: The warmed and moistened air rises, creating atmospheric instability.
• Cloud Formation: This instability leads to the development of cumulus-type clouds.
• Snowfall: These clouds produce heavy snowfall, particularly along coastal areas.

This process is frequently observed along the coasts of the Black Sea and the Sea of Marmara.

The lake-effect snow event that affected Istanbul between 17 and 19 February 2015 is a classic example of lake-effect snowfall. During this period, a cold air mass originating from the north moved across the Black Sea before reaching Istanbul. As the cold air passed over the sea, it absorbed moisture and became unstable, resulting in intense snowfall over the city.

During this event, snow depths measured 40 cm at Atatürk Airport, 39 cm at the Sarıyer Meteorological Station, 27 cm in Kartal, 18 cm at Sabiha Gökçen Airport, and 3 cm in Kumköy. Additionally, numerous flights were canceled or diverted to other airports due to the heavy snowfall.