The predictability of the Stratospheric Sudden Warming of January 2013 in various NWP systems

During the 2012-2013 winter anomalous upward propagating planetary wave activity was observed during the second and third weak of December followed by a rapid deceleration of westerly circulation around January 2, and within 3-4 days the circulation reversed on January 7, 2013. This stratospheric dynamical activity was followed by an equatorward shift of the tropospheric jet stream and a high pressure anomaly over North Atlantic, resulting in severe cold conditions in the UK and Northern Europe. A planned multi model study to estimate the predictability of the event is performed. In most of the models the event was successfully predicted by 10 days in advance. However, only some ensemble members of a few models were able to show the weakening of westerly wind by 15 days in advance. The event is recognized as the stratospheric sudden warming preconditioning by anomalous wave-1 amplification of planetary waves in the stratosphere followed by anomalous wave-2 amplifications. The models have some success in reproducing wave-1 activity by the 15 days in advance but they failed to produce triggering wave-2 activity during the final days of the event. Current skill in predicting SSWs and its consequential impact on tropospheric weather forecast in the context of stratosphere-troposphere coupling is explored. The limitations of different models in correctly simulating the event is investigated.