The NEXRAD radar network was developed by the National Weather Services in the 1980s and first deployed in the early 1990s. In the years since, advances in technology and communications have allowed them to improve the quality of radar products. The “Classic Products” in RadarScope date back to the original NEXRAD Level III product suite. Most of them of been superseded over the years by better alternatives. But they can still be useful for reference purposes or when using RadarScope on a low-bandwidth connection.
Composite Reflectivity
Composite reflectivity combines data from all elevation scans, or tilts, to create a single product. The resulting image shows the highest reflectivity value from the vertical cross section at that location. Composite reflectivity can reveal important features in a storm’s structure that might not be seen in the base reflectivity product.
Because it combines data from all the tilts, the composite reflectivity product is one of the last to be produced during a volume scan. As with all NEXRAD products, it’s important to remember that the data displayed in the image depict conditions that have already happened rather than what is happening right now.
Storm Relative Velocity
Storm relative velocity is base velocity with the average storm motion subtracted out. When storms are moving quickly, this makes it easier to spot green/red velocity couplets that are indicative of rotation and which might be masked out by the motion of the storm. As with base velocity, green is motion towards the radar and red indicates motion away. We aren’t always lucky enough to see prominent radar signatures from tornadoes. The radar isn’t looking at ground level, so it can’t actually see the tornado itself. It’s seeing rotation higher up in the storm covering an area that is several miles wide. The height and width of the radar beam increases with its distance from the radar. So the farther away a storm is from the radar, the higher up the radar is seeing and the wider the beam, making it is less likely to detect the rotation associated with a tornado. You can learn more about storm relative velocity on this National Weather Service page.
One-Hour Rainfall
The classic one-hour rainfall product estimates the amount of rain that has fallen over the past hour. It’s an older, lower-resolution alternative to the Digital Accumulation Array product.
Storm Total Rainfall
The classic storm total rainfall product estimates the amount of rain that has fallen for an arbitrary period determined by the radar operator. It’s an older, lower-resolution alternative to the Digital Storm Total product.
Vertically Integrated Liquid
Vertically integrated liquid (VIL) estimates the amount of water in a column of air. High values for VIL can indicate heavy rainfall or the presence of hail. When VIL values fall rapidly, it may indicate a downburst. VIL is subject to radar limitations and seasonal dependencies, so it’s a tricky product to interpret. The classic VIL product is a older, lower-resolution alternative to Digital Vertically Integrated Liquid.
Echo Tops
The echo tops product shows the maximum height of precipitation echoes detected by the radar between 5,000 and 70,000 feet that exceed 18 dBZ. Higher echoes are often associated with stronger areas of a storm. This product is useful for identifying strong updrafts, and a sudden drop can indicate the onset of a downdraft. Some storms are too close to the radar for the beam to see the top, so echo tops is often underestimated for strong storms near the radar. The classic echo tops product is an older, lower-resolution alternative to Enhanced Echo Tops.