Photo: NASA earthobservatory.nasa.gov/IOTD/view.php

On July 16, 2017, NASA’s Terra satellite captured this image of a mid-latitude (extratropical) cyclone off the coast of Portugal. Hot, dry, continental areas typically see lower pressure (thermal lows) than the nearby ocean. Sometimes these thermal lows become mobile and move offshore. When the image was acquired, there was a particularly strong contrast between North Atlantic and continental Europe developing cyclonic circulation. In summer, these systems tend to be slow-moving, which is why it doesn’t rain.