So, How Do Shelf Clouds Form Anyhow? (credit: Meteorologist James Spann)

DISCUSSION: During a typical severe weather season, there are a large variety of different forms of severe weather threats which evolve during a given situation based on the given atmospheric dynamics in place.  Having said that, in many cases, severe thunderstorm development nearly always involves some sort of dynamic interaction between updrafts and downdrafts.  In many cases wherein the convective storm development becomes what is referred to as predominantly “outflow dominant,” these types of convective scenarios consistently involve a storm exhibiting very impressive low-level features. When a convective storm is outflow dominant, this implies that the storm has a strong low-level air stream impinging on the back-end of the storm and forces stronger winds near the front of and/or just out ahead of the storm’s region of peak intensity.
 
One such feature which is somewhat consistently observed with many outflow dominant severe weather events is known as a shelf cloud. Shelf clouds form as a result of rain-chilled air within a strong downdraft of a strong to severe thunderstorm descending out of the base of the leading edge of the thunderstorm and then forcing relatively warmer and moister ahead out ahead of the approaching storm to be lifted.  This lifting of the relatively warmer air is directly due to the fact that this warmer air out ahead of a such a storm is warmer and moister which also means that such a storm has a greater degree of vertical buoyancy.

Hence, as the colder (storm-generated outflow) air descends both down and away from a given storm, this allows for the warmer and moister air to be lifted more easily and then often condense as well as it rises through the lowest levels of the atmosphere.  During this process of moisture condensation, there are many occasions during which this moister air condenses and is visualized by way of the development of a shelf cloud. A great example of this is captured in the image attached above (courtesy of Marty Hendickson via Meteorologist James Spann) in association with a severe storm which occurred on the afternoon of June 1st over the coastline of Palm Beach, Florida.
 
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 © 2018 Meteorologist Jordan Rabinowitz