In February 2005, unexpected heavy snowstorms lasted a couple of days with changing intensities, producing significant snowfall that eventually paralyzed the life of Istanbul metropolis. Surprisingly, there was no caution announcement prior to the onset of this unusual weather phenomenon. What was the reason behind this wrong prediction? In this case study, using a meteorological model, a heavy sea-effect snowfall, the reason of this phenomenon, was simulated and researched. With a persistent surface high-pressure center over western Russia, a surface low-pressure positioned in the center of southern Turkey was the dominant feature of the formation of the sea-effect snow over the city. In addition to strong northerly winds (19 m/s), low directional vertical wind shear (< 30(o)) and extremely long fetch distance (similar to 600 km) feature; environmental conditions during the event were characterized by a sea-surface 850-hPa temperature difference of up to 14A degrees C and a sea-land temperature difference as high as 24A degrees C.