Considering Zmax based on 2D maximum reflectivity, the threshold
was varied between 45 and 65 dBZ in increments of 1 dBZ. A maximum
HSS of 0.61 is obtained relying on the BI data as ground truth for a lower
reflectivity threshold of 56 dBZ (Fig. 3a). Implementing this threshold
yields 62% of detected events and 35% false alarms. Evaluation with
the VH data gives a slightly lower maximum HSS of 0.53 (POD =
0.55; FAR = 0.4) for a threshold of 55 dBZ (Fig. 3b). This finding approximately
confirms the 55 dBZ threshold originally considered by the
Mason (1971) criterion.