Doppler radar gets its name because it allows for the detection of motion within thunderstorms. This is a particularly useful tool when it comes to dissecting ‘spin’ within storms.
Velocity products are one of the more misunderstood imagery types within radar, and people oftentimes confuse how to read velocity.
Weather radar can see what is known as radial velocity, which is essentially if winds are moving towards or away from the radar. You can correct this somewhat with a chart known as “Storm Relative Velocity” which allows you to adjust velocity values for storm motion.
Base velocity: This is the basic velocity image to look at. You can use this chart to do things like detect strong wind gusts within storms or to see if a storm is spinning at all. But it is worth noting that this chart does have its limitations — you must always note where the radar is to determine which way the wind is blowing.
Typically red returns are moving away from the radar and green returns are moving towards the radar.
Storm relative velocity: This chart is helpful with severe storms especially because it takes into account the storm’s forward motion to give a look at the spin within a storm. Oftentimes, the forward motion within a storm can mask rotation — using storm relative velocity will correct for that and allow you better discern the presence of low-level mesocyclones as just one example.