An intercomparison of skill and over/underconfidence of the wintertime North Atlantic Oscillation in multi-model seasonal forecasts

Journal article

Recent studies of individual seasonal forecast systems have shown that the wintertime North Atlantic Oscillation (NAO) can be skilfully forecast. However, it has also been suggested that these skilful forecasts tend to be underconfident, meaning that there is too high a proportion of unpredictable noise in the forecasts. We assess the skill and over/underconfidence of the seasonal forecast systems contributing to the EUROSIP multi‐model ensemble system. Five of the seven systems studied have significant skill for forecasting the wintertime NAO at 2–4 month lead‐times. Four of these skilful systems are underconfident for forecasting the NAO. A multi‐model ensemble (ensemble size 126 members) is both skilful and clearly underconfident. Underconfidence becomes more pronounced as the ensemble size increases. Certain years in the hindcast period are well forecast by all or most models. This implies that common teleconnections and drivers of the NAO are being captured by the EUROSIP seasonal forecasts.

Authors: Baker, LH; Shaffrey, LC; Sutton, RT; Weisheimer, A; Scaife, AA

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Geophysical Union
• Journal: Geophysical Research Letters
• Volume: 45
• Issue: 15
• Pages: 7808-7817
• Publication date: 2018-07-05
• Acceptance date: 2018-06-26
• DOI: 10.1029/2018GL078838
• EISSN: 1944-8007
• ISSN: 0094-8276
• Keywords: Europe; seasonal forecasting; North Atlantic oscillation; predictablity