Why so Cloudy Lately? An Inversion is to Blame.
Well it seems as though most of December has been on the cloudy side, especially recently. Even with high pressure overhead, clouds continue to dominate the forecast. High pressure is supposed to bring sunshine, so why is it so cloudy? The answer is an inversion. The image above is an example of an inversion. This is a picture from a mountain top looking down at a city. Notice the cloud layer just above the buildings while it’s sunny just above, which is a little higher in elevation.
An inversion is when the atmospheric conditions, typically the temperature, is opposite of what a typical atmosphere would be. A normal temperature profile shows a decrease in temperature with height which means the surface is milder than the temperatures above our heads. In an inversion, temperatures increase with height and the temperatures at the surface are cooler. Inversions typically develop at night when the heat from the previous day escapes into the atmosphere and the surface becomes much cooler.
Clouds, pollution, etc can be trapped underneath the inversion. An explanation is in the graphic below. Low-level moisture in the form of clouds typically become trapped within this inversion and mixing is limited. Mixing allows the clouds to break apart and the temperatures to warm. Without mixing, temperatures likely remain on the cool side.
An inversion occurred yesterday (Sunday December 14th) when it was cloudy and cool near 50 degrees. Some computer models forecasted sunshine and obviously did not do well forecasting the proper sky condition. We will continue to see the influence of the inversion through today, especially the first half.
Inversions are tough to forecast and are almost always a challenge for meteorologists.