Pt Loma
Gene and I went to Pt Loma yesterday at low tide to poke around the tide pools and enjoy the coastal scenery. The weather was beautiful, but offshore we could see the marine layer in the distance. At one point when we were heading north along the shore, I turned around to see the southern area completely enveloped in a blanket of fog…it’s not really fog, but the marine layer air mass. It overtook us in a matter of seconds. Bizarre. Some days we wake up to find everything grey and foggy, but a short drive across the bridge and it’s clear and cloudless and it almost looks as if there’s an invisible wall holding it back at a certain point. It’s almost always present, at varying distances from the shore, and makes sunset viewing difficult. From Wikipedia:
A marine layer an air mass which develops over the surface of a large body of water such as the ocean or large lake in the presence of a temperature inversion. The inversion itself is usually initiated by the cooling effect of the water on the surface layer of an otherwise warm air mass. As it cools, the surface air becomes denser than the warmer air above it, and thus becomes trapped below it. The layer may thicken through turbulence generated within the developing marine layer itself. It may also thicken if the warmer air above it is lifted by an approaching area of low pressure. The layer will also gradually increase its humidity by evaporation of the ocean or lake surface, as well as by the effect of cooling itself. “Fog” will form within a marine layer where the humidity is high enough and cooling sufficient to produce condensation. Stratocumulus will also form at the top of a marine layer in the presence of the same conditions there
In the case of coastal California the offshore marine layer is typically propelled inland by a pressure gradient which develops as a result of intense heating inland, blanketing coastal communities in cooler air which, if saturated, also contains fog. The fog can last until midday when the heat of the sun is frequently strong enough to evaporate it. An approaching frontal system or trough can also drive the marine layer onshore.
A marine layer will disperse and break up in the presence of instability such as may be caused by the passage of frontal system or trough, or any upper air turbulence which reaches the surface. A marine layer can also be driven away by sufficiently strong winds.
