Extratropical cyclones have cold air at their cores, and they are fueled by interactions between masses of cold and warm air masses. Mature extratropical cyclones like this often feature comma-shaped cloud patterns that are the product of “conveyor belt” circulation. While heavy precipitation is often present near the low-pressure head of the comma, a slot of dry air usually trails the west side of the tail.
NASA Earth Observatory image by Joshua Stevens and Adam Voiland, using VIIRS data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Adam Voiland.