What is the range of WRAL's Doppler radar?
Posted May 3, 2008
MIKE MOSS SAYS: Zach, The range can be varied, depending on the mode we operate the radar in and in particular what pulse repetition frequency (PRF) it is set to operate at, as the time between pulses controls the maximum rabge that a target can be unambiguously observed. Also, regardless of the PRF setting, we can choose to display the sweep out to a user-defined range that may be less than the maximum. We typically do this, and usually set the radar to display returns out to somewhere between 100 and 150 miles from the transmitter (located near Clayton). The reason we don't usually run it at longer ranges is that the beam rises higher and higher above the ground as you continue outward, so that significantly different parts of rain-producing systems and storms become visible, sometimes making it difficult to compare close-in echoes with those farther away. Likewise, in cases where rather shallow-topped showers or stratiform rain areas are underway, the beam may be completely passing over the top of distant systems. Finally, the farther out the beam travels, the wider it is and therefore the lower the horizontal resolution. This can cause distant showers to appear larger than they are, or can cause separate showers at a great distance to appear as one larger echo. Note that this is not a specific characteristic of Dual Doppler 5000, but of all weather radar systems.
So, even though a weather radar might be able to see echoes a great distance away, outside of about 100-150 miles it is usually better to switch to viewing a system with a radar that is located closer to the precipitation area than that. In our case, we are fortunate to have National Weather Service sites readily available in Norfolk, Morehead City, Wilmington, Blacksburg VA and Greer SC, so that if we want to see the lower portions of precipitation areas outside of that 100-150 mile range, and see them with greater horizontal resolution, we can just switch to one of those sites in our displays.