TIP 97: LEARN A STORM’S SECRET
 
Looking at the radar is a great way to know where all that precipitation is located, but sometimes we also need to use that precipitation to tell us secrets about the storm’s inner workings. The two most common products available to radar users across the world are called “reflectivity” and “velocity.” Reflectivity is used to make the maps you’re probably used to seeing, with rainbow-colored shading that shows where the heaviest rain and snow are pouring down at the moment.
 
Velocity, meanwhile, tells us the speed that a storm is traveling by using the Doppler effect to determine how fast, say, a raindrop is moving. So, if the raindrop is moving east at 45 MPH, we can deduce that the winds in that region of the storm are blowing at around 45 MPH. This measure is extremely helpful in severe weather situations, especially during tornadoes.
 
The velocity data can rat out a tornado hiding in the rain. Most radar velocity images are shown in red and green, with reds showing wind moving away from the radar, and greens showing wind moving toward the radar. When all those red and green colors show strong winds moving in opposite directions very close to one another, you often have strong circulation in a thunderstorm or a tornado on your hands. These regions of rotation can be very subtle and hard to spot during weak tornadoes, and obvious during the most violent storms.