May 21 - July 31
Mapping Precipitation Intensity to Radar Observations and Derivatives
Elizabeth Sims
What is already known:
- Winter storms produce a wide range of precipitation types such as rain, snow, ice pellets, and freezing rain.
- Winter precipitaiton is a public safety concern due to its impact on transportation and other public services.
- Hydrometeor classification algorithms, including one being deployed in MRMS, typically predict only precipitation type.
- The type of precipitation and amount of precipitation can both be important, so decisions can be improved with identification of type and intensity.
What this study adds:
- A feasibility assessment of the potential for including intensity as a part of the MRMS surface hydrometeor classification algorithm.
- Overall, ASOS intensity did not correlate well with MRMS measures of intensity.s
- Results for mapping ASOS observations of intensity for rain to MRMS variables is inconclusive, so further studies will be needed to make final conclusions.
- Mapping ASOS observations of intensity for snow to MRMS variables is unlikely.
Abstract:
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 things are underway.