LAUSR

Arctic cyclones (ACs) are a severe atmospheric phenomenon that affects the Arctic environment. This study assesses the forecast skill of five leading operational medium-range ensemble forecasts for 10 extraordinary ACs that occurred in summer during 2008–2016. Average existence probability of the predicted ACs was>0.9 at lead times of ≤3.5 days. Average central position error of the predicted ACs was less than half of the mean radius of the 10 ACs (469.1 km) at lead times of 2.5–4.5 days. Average central pressure error of the predicted ACs was 5.5–10.7 hPa at such lead times. Therefore, the operational ensemble prediction systems generally predict the position of ACs within 469.1 km 2.5–4.5 days before they mature. The forecast skill for the extraordinary ACs is lower than that for midlatitude cyclones in the Northern Hemisphere but similar to that in the Southern Hemisphere. Plain Language Summary The shipping on the Northern Sea Route has become more accessible due to the recent sea ice loss. Meanwhile, such human activity over the Arctic is exposed to risks of severe atmospheric phenomena, including Arctic cyclones (ACs). As the AC frequency reaches its peak in summer and ACs can affect the Arctic environments like sea ice and wave height, the planning of ship routes requires an accurate prediction of extraordinary ACs, particularly their positions. This study assesses the forecast skill of operational medium-range ensemble forecasts for 10 extraordinary ACs that occurred in the recent decade. The results show that average central position error of the predicted ACs is less than half of the mean radius of the 10 ACs 2.5–4.5 days before their mature stage, with a central pressure error of 5.5–10.7 hPa. The forecast skill for the extraordinary ACs is lower than that for midlatitude cyclones in the Northern Hemisphere but similar to that in the Southern Hemisphere. These results are useful for using and improving numerical weather predictions over the Arctic.