Using Dual-Pol Radar during Snow Showers and Non-Meteorological Targets

National Weather Service radars are equipped with technology that can help identify the type of weather we're seeing (rain, snow, hail, etc) and meteorologists use this information during severe (and routine) weather operations to make decisions and provide support to our partners. During the early morning hours on January 4th, a weather system produced scattered to numerous snow showers across the lower Ohio Valley and the image below is what the dual-pol radar out of the Cincinnati area showed at the time.

Reflectivity: Echo intensity, or how strong the target the radar is sampling

ZDR (Differential reflectivity): The difference between the horizontal and vertical pulses of what the radar is seeing. In other words, is the shape of the hydrometer more like a hot dog or a hamburger

Correlation Coefficient (CC): How similar in shape/size. Are all the objects being sampled similar?

Hydrometer Classification (HC): The radar alogrithms' best guess as to what it is seeing (based on research and field tests)

Notice in the reflectivity (top left) that are 2 areas of interest (highlighted by white and yellow outlines). Both have similar values of reflectivities and using this alone, a meteorologist would likely assume both are snow showers (given the environment). However, using the correlation coefficient (CC), it is very obvious that these features have very different characteristics. The bottom right feature (yellow outline) has high CC values, meaning the radar is sampling targets that are very similar and is typical of rain or snow. The other feature (white outline) has very low CC values, meaning what the radar is sampling is a mix of different shapes, sizes, etc. When CC values are this low, it typically means it's non-meteorological. In addition, the ZDR values for both of these features are very different, indicative that they are not the same targets. Finally, the hydrometer classification alogrithm correctly identified the non-meteorological target as 'unknown' while showing the rest of the real snow showers were 'dry snow.' It is unclear exactly what the non-meteorological targets are - possibly birds taking off around sunrise?

NWS meteorologists in Wilmington, OH were able to diagnose this and provide decision support to their partners as these snow showers (or not) moved through the area during the peak of the morning rush.