Seasonal winter forecasts and the stratosphere

• Published in: Atmospheric Science Letters
• Main Authors: Scaife, A. A., Karpechko, A. Yu., Baldwin, M. P., Brookshaw, A., Butler, A. H., Eade, R., Gordon, M., MacLachlan, C., Martin, N., Dunstone, N., Smith, D.
• Other Authors: Suomen Akatemia
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://dx.doi.org/10.1002/asl.598; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fasl.598; https://onlinelibrary.wiley.com/doi/pdf/10.1002/asl.598; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/asl.598; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/asl.598

Abstract We investigate seasonal forecasts of the winter North Atlantic Oscillation (NAO) and their relationship with the stratosphere. Climatological frequencies of sudden stratospheric warming (SSW) and strong polar vortex (SPV) events are well represented and the predicted risk of events varies between 25 and 90% from winter to winter, indicating predictability beyond the deterministic range. The risk of SSW and SPV events relates to predicted NAO as expected, with NAO shifts of −6.5 and +4.8 hPa in forecast members containing SSW and SPV events. Most striking of all is that forecast skill of the surface winter NAO vanishes from these hindcasts if members containing SSW events are excluded.