Archive for November, 2013

Kelvin-Helmholtz Wave Clouds
November 18, 2013

Hotshots3 Photo by: Kathleen Dimmel, Navasota

These cloud-waves rarely occur because you need almost perfect atmospheric conditions.  Much like ocean waves, the air on the tops of these clouds is moving faster than the bottom of the clouds.  The clouds near the surface are cooler than above and the wind speeds are light, like fog.  Over the low clouds is a warmer and faster-moving layer of air creating the crest, like we see in the ocean.

Hotshots2

Rita Casserly sent in this picture.

 

This is probably the best example from Birmingham, Alabama.

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Roll Clouds
November 18, 2013

RollCloud_Houston

It’s called a roll cloud — low, horizontal, tube shaped, and completely detached from the cloud base near it. They are rare to see but when present they are located on the leading edge of a line of thunderstorms, cold fronts or squall lines.

Roll clouds form when cool air sinking from a storm cloud’s downdraft spreads out.  This is called a gust front. This outflow undercuts warm air being drawn into the storm’s updraft. As the cool air lifts the warm moist air water condenses creating this kind of cloud, which rolls with the different winds above and below.

While they look like tornadoes turned sideways, they are not and do not produce tornadoes.

RollCloud_BrianGrimm

Photo by: Brian Grimm, Crosby

RollCloud_Lou

Photo by: Vanessa Rich, Vinton, LA

You can e-mail your cloud pictures to: hotshots@click2houston.com