Marine Cloud Cover: Friend or Foe?

So the old question asked to the weather center (from the newsroom and public) is: How can the forecast numbers be so affected by the clouds we see off the ocean?

Marine layer clouds are just that- layers of clouds that have an origin of marine air. On the East Coast, that doesn’t mean that much, because they generally hang offshore. But here on the west coast, its a game-changer. Or in our case, a forecast changer.

Take today for example: The picture above is a visual satellite image from this morning. Note how gray and opaque the clouds are draped over top of most of Western Oregon. Marine clouds are thick AND form just above the ground. We had a steady west wind at 850mb which is just a few thousand feet above the ground. We use that pressure height a lot to determine what the surface temperature will be and where the low clouds will be moving in from. Winds stayed westerly at 850 almost all day so we weren’t able to get a different wind direction to stir any of those thick clouds up and thus inject some drier air which would thin them out and “break” them up so to speak.

Think of it like making pancake batter: The mix you put in doesn’t mean that much until you add the water and batter. The more mix you add, the thicker the batter. It becomes heavier and the only thing to “thin” it out is by stirring. Since we had little stirring today, the temperatures “underneath” the clouds are very slow to rise as radiation from the sun can’t fully blast through the pancake batter. and some places don’t reach the 70s (see Portland), while others that did see sunshine (see Roseburg) got into the 80s.  So it can and usually does cause forecasting headaches here in the weather center.

If they ever come up with a cake stirrer the size of Texas, I’ll be the first in line for Oregon and our marine layer friend …


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