A cold snap that dropped temperatures 20-40°F (11-22°C) below normal helped paint a pretty picture in white over the Atlantic Ocean in early January, 2014. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite captured this true-color image on January 7 as it passed over the region.
The dramatic, parallel bands of cumulus clouds are known as cloud streets, and are formed when cold air passes over relatively warm water, while a layer of warmer air (a temperature inversion) lies over both. The comparatively warm water gives up heat and moisture to the cold air above, and columns of heated air called thermals rise upward through the atmosphere. When the rising thermals hit the warmer inversion, which acts like a lid, the thermals roll over and loop downward, creating parallel cylinders of rotating air. As this happens, the moisture cools and condenses into parallel rows of clouds.
Clouds streets are aligned with the prevailing winds; the direction of the predominantly northwesterly winds on January 7 is clearly written in the clouds.