This week’s satellite image is from this morning over Colorado. It is not a visible satellite image, as I often post, but rather a water vapor image. This means that the sensors on the satellite are recording wavelengths outside the visible spectrum, instead recording the reflections of this wavelength off the water droplets in the atmosphere between roughly 700 mb to 400 mb high.
Notice how the moisture seems to bunch up in central Colorado, and it is drier on the opposite side of the mountains.
What we are seeing is the winds are blowing towards the mountain, and forced up the western side. As the air travels upward, it cools and expands, and some of the moisture condenses out. This is how both dew and clouds form, and explains the “bunching up” of moisture on the windward side of the mountain.
Once the winds cross the peak of the mountain, they sink down the opposite side. The sinking causes the air to compress, which helps it warm up. Also, as the air sinks it warms due to the warmer environment as it approaches sea-level. This sinking air, and the fact that some of the moisture condensed out (and was thus left on the windward side of the mountain) is why we see dry signatures on the leeward side of the mountain.
This can set up a dangerous situation. The air on the leeward side is dry and can be gusty through the mountains. This is the perfect recipe for wild fires, if there is a source of ignition and good fuel about, especially if this has been occurring for several days and has dried out the wooded areas.
Thank you for reading this post!
Source: College of DuPage – SATRAD