File:Open-cell clouds over Tasmania (MODIS 2017-02-17).jpg

English: After a period a period of extreme heat, including the hottest day on record (116.6˚F/ 47˚C) in New South Wales as well as the worst fire weather on record in that state, a high pressure system in the Great Australian Bight brought some relief to South Australia and New South Wales on February 13, 2017. The approaching high also triggered cold temperatures in Tasmania and Victoria. Hobart, the largest city in Tasmania, reported high temperatures of a cool 65˚C (18.3˚C) on that day. The day was also windy, with clouds and rain.

The Terra satellite was moving over Tasmania on that same day, allowing the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard to acquire a true-color image of the cloudy scene.

The primary cloud seen in this image is the open-cell cloud, which covers the southeastern section of the image. Open-celled clouds look like an open honeycomb, with lines of clouds tracing the cell borders and the center of the cell remaining cloud-free. A counterpart to this type of cloud, the closed-cell cloud, is also formed on the honeycomb shape, but the center of those cells are filled with cloud.

Both open- and closed-cell clouds get their general shape from Rayleigh-Bernard cells, the hexagonal patterns that form naturally when fluids are heated from below. The main difference between the two cloud types relates to the flow of air. Moist, warm air rises in the center of closed cells and sinks around the edges. Open-cell clouds have air sinking in the center of cells and rising along the edges. In both cases, clouds form when parcels of warm air rise, expand, and cool enough for water vapor to condense into liquid droplets.