What do the colors mean on a supercell radar image?

Answer 1

It depends on what type of image you are looking at. The most common type of image is a reflectivity image, which is how much of the radar signal is bounced back. For the most part, this represents how heavy it is raining. Blue and green (low reflectivity) is light to moderate rain while red (high reflectivity) is very heavy rain. Deep red and violet often indicates hail. In some rare cases there is an area of high reflectivity called a debris ball, which forms when a tornado is causing major damage and lifting debris high into the air. Many supercells have a hook-shaped area of reflectivity called a hook echo that indicates roatation that can lead to the formation of a tornado.

Sometimes, particularly with supercells, there will be a velocity image, which shows how fast rain drops and other material is moving towards or away from the radar, used a a proxy for wind speed. In these images, green indicates wind blowing toward the radar (relative to the moiton of the storm) while red indicates wind blowing away from the radar. Brighter colors mean higher velocities. In some cases blues an yellows are used in place of green and red for the highest velocities, something usually only seen during violent tornadoes. Velocity images are often used to find a velocity couplet, and areas where high velocities both toward and away from the radar occur in a small area, indicateing strong rotation.

See the image linked below for an example. At the time that this image was taken, an EF5 tornado was tearing through Joplin, Missouri. The image on the left shows reflectivity. The hook echo with a debris ball at the end is near the "Joplin" marker. The image on the right shows storm relative velocity. The velocity couplet, near the "Joplin" marker shows the location of the tornado.