2015 Volume 11 Pages 59-64
The influence of large-scale atmospheric blocking over the northwestern Pacific on heavy snowfall events in the Kanto area and on the Pacific Ocean side of northern Japan (PNJ) within the time scale of ∼10 days was examined through blocking case studies. The past 14 blocking cases over the Pacific, including the blocking during early- to mid-February 2014 that influenced a record-breaking snowfall over the Kanto area, were analyzed using a long-term reanalysis dataset and local meteorological observation station data. Results reveal that blocking over the Pacific causes large precipitation over the Kanto area and the PNJ by shifting cyclone (storm) tracks towards the east coast of Japan from their usual eastward course across the mid-Pacific via the south coast of Japan. Excessive passing of cyclones caused large precipitation in the Kanto area and snowfall in the PNJ. In the blocking cases with heavy snowfall events in the Kanto area, a strong cold-air inflow over Japan also existed in the lower troposphere originating from east Siberia, which initiated synoptic ground cold-air environments in the Kanto area.