URP Hail Algorithm
n
Uses a algorithm developed in southeastern Australia (the Sydney area). Two approaches are used, the one giving the largest hail size is chosen. The first approach correlates hail size with the freezing level and the height of the 50 dBZ echoes. As you can see, the correlation is not strong.
Hail size is determined by empirically correlating the freezing level height to the maximum height of the 50 dBZ echoes.
The second approach estimates hail sizes based on the correlation between freezing level height and VIL as in the figure below. Once again, the correlation is not strong.
Hail size is determined by empirically correlating the freezing level height to the VIL.
Some modifications to the algorithm have subsequently been done in Prairie and Northern region:
- A correction was applied to account for the different terrain heights on the Canadian Prairies. The Australian work was essentially done at sea-level so the freezing level heights were ASL. The correction meant that the freezing level height was determined above ground (AGL).
- During the development of the Australian algorithm, observations were gathered close to the radar site; essentially, they were co-located. A correction was applied to calculate freezing heights AGL, where the cells were on the Prairie radars. This was done use Global Environmental Multi-scale (GEM) model output.