Storm Object Size Analysis in a 1-km Warn-on-Forecast System Prototype

A 1-km Warn-on-Forecast System prototype (WoFS-1km) was run in pseudo-realtime during the 2021 and 2022 Hazardous Weather Testbed Spring Forecasting Experiments. This prototype is under development as the traditional WoFS has a 3-km model grid spacing (WoFS-3km) and cannot resolve some convective processes. Recent studies have shown that WoFS-1km is more accurate in depicting reflectivity objects than both WoFS-3km and 1-km forecasts downscaled from 3-km analyses (Wang et al. 2022; Kerr et al. 2023). However, these previous studies use a minimum object area threshold and do not consider smaller storm objects that may be better resolved by WoFS-1km than WoFS-3km. In this presentation, the focus shifts to these smaller storm objects (area < 100 km²). The size distributions of forecast objects matched to observed objects (“hits”) and false alarm forecast objects reveal WoFS-1km and 1-km downscaled forecasts have more small objects than WoFS-3km. This is the case for both hits and false alarms. Binning these statistics by forecast lead time shows which lead times WoFS-1km can be most beneficial over 1-km downscaled forecasts for small object forecast accuracy.