Marine-Influenced Snowfall (MIS)

Sea-effect snow is a type of precipitation that occurs due to instability generated when polar cold air masses pass over relatively warmer sea or lake surfaces, acquiring heat and moisture. During this process, the cold air mass warms and gains moisture 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.

Formation of sea-effect snow. (Generated by artificial intelligence.)

Formation Mechanism

The formation process of sea-effect snow occurs in the following steps:

• Cold Air Flow: A cold air mass moving from the north warms and gains moisture as it passes over the sea or lake surface.
• 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 intense snowfall, particularly along coastal areas.

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

The Sea-Effect Snow Event in Istanbul on 17–19 February 2015

The sea-effect snow event that affected Istanbul between 17 and 19 February 2015 is a typical example of this phenomenon. During this period, a cold air mass originating from the north passed over the Black Sea before reaching Istanbul. As the cold air moved across the sea, it absorbed moisture and became unstable, resulting in heavy snowfall across 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, due to the intense snowfall, many flights were canceled or diverted to other airports.