Onshore Flow

Onshore flow is the movement of air from the ocean (or a large body of water) onto the land, driven by the temperature difference between the cooler water and the warmer land. During the day, the land heats faster than the water, creating a pressure differential that drives cool, moist marine air inland.

Aviation Significance

Onshore flow is a key ingredient in advection fog formation along Canadian coastlines. When warm, moist air is advected from the ocean over colder land surfaces, or when a cool marine air mass replaces warmer inland air, fog and low ceilings can develop rapidly and persist for extended periods.

Sea Breeze

The classic form of onshore flow is the sea breeze — a thermally-driven local circulation that develops on sunny days along coasts and large lakeshores. The sea breeze front can be a trigger for convective development, and the sharp wind shift at the front can create turbulence and wind shear at low levels.

Related Terms

See also: Advection Fog, Low-Level Wind Shear.