A spectacular, though fleeting, display of low-level cloud streets were visible over the Kansas City metro area Wednesday morning as strong low- and mid-level southerly flow usured in moisture from the south.
Cloud streets generally orient themselves parallel to the low-level flow, with a slight slant of 10-20 degrees to the left. This orientation was evident this morning as strong southerly flow created streets that were generally oriented from the south-southwest to the north-northeast.
Cloud streets generally form within the lowest mile or so of the atmosphere – a region known as the planteary boundary layer. This is the area where upper-level winds and low-level winds mix and great interesting phenonmenon when conditions are suitable.
In the case of cloud streets, winds that are relatively constant speeds with height will create favorable conditions. Though wind speeds are generally constant, multiple sources of thermal currents from below will give rise to a series of rolls that become visible when moisture condenses into clouds.
This effect is strengthened when a low-level temperature inversion is in place — that is, when temperatures at lower levels are cooler than temperatures at higher levels. The inversion acts as a ‘cap’ on the atmosphere, preventing further upward motion, as colder air is less buoyant than warmer air. This turns the rising thermals around, generating the ‘rolling’ motion necessary to create the clean edges seen in the cloud streets.
In the case of the Kansas City display today, the steets were not visible from visible satellite imagery, as higher-level clouds covered the low-level streets, though cloud streets have been visible in satellite photographs in the past when upper-level clouds aren’t present.