NASA's Terra satellite "drove over" the cloud streets in Hudson Bay, Canada on November 20, 2011 at 12:25 p.m. EST (17:25 UTC). These rows of clouds stretch from northwest to southeast over the Hudson Bay.

A "cloud street" appears to be long horizontal rolls of clouds. Cloud streets are basically long rolls of counter-rotating air, and they are parallel to the ground. These are basically eddies in the atmosphere that help transport moisture, heat and pollutants within the boundary layer of the atmosphere.

According to NASA's Earth Observatory, cloud streets form when cold air blows over warmer waters, while a warmer air layer—or temperature inversion—rests over top of both. The comparatively warm water of the ocean gives up heat and moisture to the cold air mass above, and columns of heated air—thermals—naturally rise through the atmosphere. As they hit the temperature inversion like a lid, the air rolls over like the circulation in a pot of boiling water. The water in the warm air cools and condenses into flat-bottomed, fluffy-topped cumulus clouds that line up parallel to the wind.

Hudson Bay is a large body of saltwater located in northeastern Canada. It drains a very large area, including parts of Alberta, Ontario, Quebec, Saskatchewan, much of Manitoba and southeastern Nunavut, all of which appear snow covered in this image. It also drains into parts of North and South Dakota, Minnesota, and Montana.

Also in the image, are several snow-covered islands in Hudson Bay. The larger island to the north is South Hampton Island, and the smaller island east is Coats Island, and further east is Mansel Island. Image: NASA MODIS Rapid Response Team. Caption: NASA, Rob Gutro and NASA's Earth Observatory

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