Abstract
The winter of 2019–2020 was dominated by an extremely strong stratospheric polar vortex and positive tropospheric Arctic Oscillation (AO). Here, we analyze forecasts from six different prediction systems contributing to the C3S seasonal forecast database. Most performed very strongly, with consistently high skill for January–March 2020 from forecasts launched through October–December 2019. Although the magnitude of the anomalies was underestimated, the performance of most prediction systems was extremely high for a positive AO winter relative to the common hindcast climate. Ensemble members which better predicted the extremely strong stratospheric vortex better predicted the extreme tropospheric state. We find a significant relationship between forecasts of the anomalous midlatitude tropospheric wave pattern in early winter, which destructively interfered with the climatological stationary waves and the strength of the stratospheric vortex later in the winter. Our results demonstrate a strong interdependence between the accuracy of stratospheric vortex and AO forecasts.
Plain Language Summary
Westerly winds during the winter of 2019–2020 were unusually strong and long lasting through a deep layer of the atmosphere. We investigate how well this was predicted months ahead of time. We find that seasonal weather forecast systems predicted the winter pattern very well, especially when compared with previous winters. Forecasts which better predicted the strength of the winds higher in the atmosphere did better overall. We find that there was a link between predictions of the weather patterns lower down in the atmosphere and how they suppressed large-scale atmospheric waves in the midlatitudes, which likely helped the winds remain stronger higher up.
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https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL090328
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De discussie over het nut van winterverwachtingen komt elk jaar wel terug. Een fraaie traditie 
De ene winter laat zich beter voorspellen dan de andere. Soms is er een krachtige driver aanwezig die e.e.a. eenvoudig maken. Soms spelen meerdere een rol en dan is het al een stuk lastiger.
Een voorbeeld van een eenvoudige winter was die 2020. Het is dus zaak -voor wie daar mee bezig is- om goed te weten wanneer je wel/ niet op de modellen kunt rekenen en welke drivers aanwezig zijn die daar invloed op hebben. Een ambacht.