On March 19, 2020, a broad low-pressure system hung over the Pacific Ocean off the west coast off of North America. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of the system on that same day.
Generally, high- and low-pressure systems form when air mass and temperature differences between the surface of the Earth and the upper atmosphere create vertical currents. In a low-pressure system, these vertical winds travel upwards and suck air away from the surface of the Earth like a giant vacuum cleaner, decreasing the air pressure above the ground or sea. This decrease in surface air pressure in turn causes atmospheric currents moving parallel to the surface of the Earth near the base of the low to spin counter clockwise (clockwise in the Southern Hemisphere).