National Weather Service radar assigns each thunderstorm that develops
or moves into the range of a particular site, within the composite
reflectivity product, a tracking code. This code consists of one letter
followed by one number, such as in X1. Use this code to locate the cell
on the radar.
reason some of the characteristics may be different pertains to the
vertical level at which the storm was scanned, which depends on the
cell's distance from the radar. Best imagery is usually taken close to
a radar site, but not above it, allowing for all of the beams sent by
the radar to reflect off the cell.
given thunderstorm may or may not retain the cell identification code
between radar scans. This is largely dependent on how consistent the
storm is, by means of development and growth, between runs. If the
radar believes a new cell has formed, it will identify it with a new
tracking code, even though it may have been a detected storm in
previous runs that changed structure. Two tracking codes could be
assigned to one storm if it appears to the radar that the cell is
splitting into two new storms. A linear squall line or bow/comma echo
usually has several identification codes.
A thunderstorm that is very near or above the radar site may not be
detected because the radar's beams are unable to tilt at such an angle.
A cell identification code will likely not be assigned to such a cell,
which will tend to have poor and inaccurate reflectivity. Even cells
that had a tracking code at one point may lose them.