Mapping Precipitation Intensity to Radar Observations and Derivatives

This is a feasibility study to investigate whether a 2-D analysis of precipitation intensity (i.e., light, moderate, heavy) can be derived from existing products within the Multi-Radar/Multi-Sensor (MRMS) system in order to better detect events with rapidly-accumulating snow or ice. This is done by comparing Automated Surface Observing System (ASOS) observations of intensity to various MRMS fields, including base reflectivity, composite reflectivity, and instantaneous precipitation rate for the 2016/17 winter season. Since there is a rather limited number of mixed phase and refreezing habits, only pure classifications of rain and snow (RA and SN) are considered. Even when the data were filtered to include only SN events with low wind speeds and only sites that are within about 50 km of the nearest radar, no meaningful correlation between SN intensity and the MRMS fields was found. There was a clearer correlation between RA intensity and the MRMS fields. However, the different intensity categories still had significant overlap indicating that any threshold based on a single MRMS field will result in a significant number of misclassifications. An attempt to define intensity based on linear and nonlinear combinations of multiple MRMS fields was also made, but again, a clear set of discriminants could not be found. While these results are largely unpromising, it is possible the low correlations could be due to the way in which the ASOS observations were partnered with the MRMS data. It is also possible that other fields, such as echo depth, may provide improved correlation. Efforts to investigate these additional methodologies are discussed.