Developing and evaluating week 2 and weeks 3-4 outlook tools for extratropical storminess

Extratropical cyclones give rise to most of the high impact weather in mid-to high-latitudes during cool seasons, including heavy precipitation and strong winds. Thus it is important for stakeholders be informed approaching periods increased or decreased cyclone activity. While individual tracks can predicted out about a week so, from 2 on, statistics summarizing activity, storminess, are more useful. Storminess defined based on Lagrangian tracking by Eulerian variance statistics. The outlook includes combination both methods. provide information where pass through intuitive users, while have been shown highly correlated with cyclone-related expected predictable given that they not as noisy. In this paper, we evaluate storminess tool developed dynamical model forecasts week-2 weeks 3-4 time ranges. uses two 6-hourly subseasonal ensemble forecasts–the Global Ensemble Forecast System version 12 (GEFSv12), coupled Climate (CFSv2). Hindcasts operational 1999–2016 used assess prediction skill. Our results show GEFSv12 CFSv2 combined has higher skill than either ensemble. shows some predicting amplitude frequency 3-4, highest winter, lowest summer. Models also deep 2. skills an sea level pressure metric significantly those track performs better its predecessor GEFSv11. Correlations between indices surface weather, winds, examined. A publicly accessible web page display predictions real time. contains climatology forecast verification enable users make use outlook.