Saturday, July 25, 2009

More Than Two Simple Words

While much of the rest of Washington is basking in warm summer temperatures and sunny skies, that large orange ball has been having a hard time appearing in the sky over South Bend. For the first time in several days, we received a brief glimpse of it this afternoon before it disappeared again. The prime reason we're missing out on the fun and sun boils down to two words: marine layer.

If you don't live on the coast of an ocean or a large lake (e.g., the Great Lakes), you probably don't have much experience with the marine layer. Of all the various environmental and climatic factors that influences our weather, the marine layer plays one of the biggest roles. It helps to explain why our temperatures tend to be cooler in the summer and warmer in the winter than communities only a few miles inland.

This is what Wikipedia has to say about the marine layer:
A marine layer is 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. Stratus and stratocumulus will also form at the top of a marine layer in the presence of the same conditions there.
About one week ago, the marine layer made a significant difference in weather in a stretch of a mere 4 miles. In Raymond -- only 4 miles east of here -- the skies were clear and the temperature hovered around 70 degrees. On that same day, we were completely socked in by clouds and our temperature never made it out the 50s. This in the middle of July!!

What was really cool is that a very definitive dividing line could be seen from the highway. As I looked downriver, I saw the clouds dissipate about 1 1/2 miles to our east. Just beyond this line, one could see the shadows of the sun, but I was standing in misty fog. It was sort of surreal.

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