The Tohoku region (along with Hokkaido) exists overthe Okhotsk Plate, which is bounded on the north by the North American Plate and on the east by the Pacific Plate. The Pacific Plate that exists off the east coast of Tohoku converges underneath the Okhotsk Plate at the Japan Trench, which is an ocean trench that is a part of the Pacific Ring of Fire, in the floor of the northern Pacific Ocean. This convergence results in continuous movement causing an unusual number off earthquakes of the Northeastern coast of Japan. In addition to the Magnitude 9 earthquake on March 11th, 2011, there is research proving two other earthquakes of Magnitude 9 occurred along the Pacific coast from Hokkaido to the Tohoku region over the past 3000 years.
The Tohoku region is divided into 4 different climate areas: 1) the coastal areas of the Japan Sea (west Aomori, west Akita, west Yamagata), 2) the Nasu Volcanic Zone and western basin (north central Aomori, central east Yamagata, west Fukushima), 3) the eastern basin of the Nasu Volcanic Zone, but not including the Nasu Volcanic Zone (northern Aomori, west central Iwate, west central Fukushima), 4) and the coastal areas of the Pacific Ocean (east Aomori, east Iwate, Miyagi, east Fukushima). All four areas have different climate tendencies and with the exception of the Pacific coastal areas of Miyagi and Fukushima all areas are part of Japan’s great snowbelt.
Areas 1 and 2 experience a Foehn Phenomenon creating a warm and dry air that flows down the backside of the central mountains to the Japan Sea creating many clear days and high summer temperatures, but offset by warm and cool nights. In the winter months there is little sunlight with many areas becoming a snowbelt, especially the western basin of the Ou Mountain Range.
Area 3 in the summer experiences a mix of high temperatures caused by a Foehn Phenomenon and mild cloudy days along the Pacific coast, and in the winter it experiences a cold air mass from the north and west wind streams with heavy snow falls similar to the coastal areas of the Japan Sea, but with substantial clear weather along the Pacific coastal areas.
In the summer, the northern and central areas of Area 4 are usually cloudy with mild temperatures and every few years the area experiences a “Yamase,” which is cold wind stream from the north that creates a cold summer effect following the rain season (mid June to late July). In the south, the high air pressure of the Pacific Ocean creates high temperature and clear skies. In the winter, the central and southern areas experience little snow and have dry and clear weather.