The higher the dBZ, the stronger the rainrate. Typically, light rain is occurring when the dBZ value reaches 20. The scale of dBZ values is also related to the intensity of rainfall. The value of the dBZ depends upon the mode the radar is in at the time the image was created. Notice the color on each scale remains the same in both operational modes, only the values change. The other scale (near left) represents dBZ values when the radar is in precipitation mode (dBZ values from 5 to 75). One scale (far left) represents dBZ values when the radar is in clear air mode (dBZ values from -28 to +28). Each reflectivity image you see includes one of two color scales. The dBZ values increase as the strength of the signal returned to the radar increases. So, a more convenient number for calculations and comparison, a decibel (or logarithmic) scale (dBZ), is used. Reflectivity (designated by the letter Z) covers a wide range of signals (from very weak to very strong). "Reflectivity" is the amount of transmitted power returned to the radar receiver. Bright reflectivity returns that are stationary and appear during both calm and inclement weather are usually land-based obstructions such as mountains, trees, or especially wind farms (nothing gets electromagnetic signals confused like spinning metal blades!).The colors are the different echo intensities (reflectivity) measured in dBZ (decibels of Z) during each elevation scan.This is helpful for picking out snow/mix/rain transition zones In all snow situations, dBZ values of 40 indicate 3-4”/hr snowfall rates and whiteout conditions. Anything larger than this is usually due to “bright banding” where the radar is seeing the part of the atmosphere where snowflakes are clumping together and melting into raindrops.
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