Echo size and asymmetry: impact on NEXRAD storm identification

Abstract

The effects of echo shape and radar viewing angle on detecting small thunderstorms with the NEXRAD storm identification algorithms are examined. The amorphous low level echo shapes are modelled as ellipses with major axes ranging from 5-15 km and minor axes varying between 2-5 km. The model echoes are then used to create a "probability of detection' chart that demonstrates the impact of storm asymmetry on cell identification. A new algorithm based on the analysis of 15 storms observed in Florida, Alabama, and New Mexico is proposed that would identify storms as having lightning if 40 dBZ reflectivity is present at the -10°C level and the echo top exceeds 9 km. This algorithm would have a 100% probability of detecting lightning producing storms 4-33 min before the first flash, a 7% false alarm rate and a critical success index of 93%. -from Authors