NEXRAD Aims to Stop Purple Haze

The NWS says in a PDF released last month that a new range-folding algorithm will soon be included in NEXRAD radar software that will significantly reduce range-folding in velocity data. Below is an example of the before and after shots. Impressive.

For non-radar-enthusiasts, PURPLE=BAD. What this breakthrough means is simply that we'll have much less missing wind data on radar maps in the future. When the radar sends out signals to detect winds, it waits to hear the signal come back. In some cases, it can't tell whether the answer back came from the original transmission or not. This data gets marked a purple color on NEXRAD displays, indicating that the radar can't determine which way the particle of precipitation is moving, or at what speed. Sometimes called "purple haze", the phenomenon can hide or obscure tornadic twisting of the winds.

They explain:

The American Meteorological Society defines range-folding, or range-aliasing, as follows.

The improvement is associated with "Build 9" of the software and will be distributed to NEXRADs across the nation during the latter half of 2007.