Recall from the previous post that a close low formed over Utah yesterday and was forecast to move southward to the Gulf of California by Wednesday. The circulation center is presently parked over the Lower Colorado River Valley, with easterly–northeasterly upper-level flow over southern Nevada where several dark bands cut across the flow in the water vapor imagery.
These dark bands result from mountain waves induced by flow over the ranges of southern Nevada. The water vapor channel is very sensitive to the amount and temperature of water vapor in the upper troposphere. The dark bands are generated in areas where the mountains cause the air to sink, warm, and dry. The band near the head of the arrow appears to be related to flow over Mt. Charleston and other high topographical features east of the Amargosa and Pahrump Valleys along the CA-NV border.
These mountain waves are only briefly detectable in conventional infrared satellite images because the air is too dry and clouds are only generated for a short time at the beginning of the loop in areas where the mountain waves are causing rising motion. For most of this period, the atmosphere is "severe clear."
Mountain waves are sometimes associated with aircraft turbulence, which can be particularly problematic when there is wave breaking in the atmosphere, which is similar to wave breaking on the beach.
|Source: Whiteman (2000)|
Thus, water vapor imagery can be useful for helping anticipate areas of clear-air turbulence.