RadarScope provides both the Hydrometeor Classification and the Hybrid Hydrometeor Classification output. While both serve the same general purpose, identifying precipitation type, there are some fundamental differences between the two.
The Hydrometeor Classification Algorithm uses several radar products to determine the precipitation type of what is being observed. One important issue to keep in mind is that this algorithm is determining the precipitation type at the beam height, not at the surface. What this means is precipitation at the beam height may be one type (for example, snow), but once it reaches the surface, it could have melted and therefore would be a different type (rain). Additionally, the Melting Layer Detection Algorithm is used in assigning a precipitation type. One major drawback of this algorithm is it assumes the precipitation does not refreeze. As a result, frozen precipitation such as sleet that is observed at the surface may be identified as rain.
The Hybrid Hydrometeor Classification Algorithm is an alternative product produced by the Hydrometeor Classification Algorithm. The hybrid algorithm utilizes the lowest available hydrometeor classification output at each radar range bin (accounting for beam-blockage) to assign a precipitation type to that range bin. The information from this scan is then fed into equations that determine both one hour and storm total precipitation. As the precipitation type changes so does the relationship between reflectivity and precipitation amounts. Based on the information received from the scan, the proper algorithm relating reflectivity and precipitation amount are selected. This algorithm is applied and a precipitation type is assigned. Below is a comparison of the two algorithms from a recent snow event in Colorado.
Comparison of Hydrometeor Classification and Hybrid Hydrometeor Classification Algorithms
While the hybrid algorithm appears to be a more accurate representation of precipitation type, it’s important to note that both algorithms are considered to be works in progress and are susceptible to errors. In order to gain more insight into precipitation type, other products (especially the dual polarization products) should be utilized. This information, combined with other meteorological data, can provide a clearer picture of what the radar is actually observing.