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Climate of Tohoku district

Location of Akita City and Sendai City

Figure 1 Location of Akita City and Sendai City

Seasonal variation of meteorological elements in Akita City Seasonal variation of meteorological elements in Akita City
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Figure 2 Seasonal variation of meteorological elements in Akita City
Left panel: The green, red and blue lines indicate monthly averages of daily mean, maximum and minimum temperatures, respectively. The blue and brown bars show monthly precipitation amounts and monthly sunshine durations, respectively. Right panel: Purple bars indicate monthly snowfall amounts.

Seasonal variation of meteorological elements in Sendai City Seasonal variation of meteorological elements in Sendai City
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Figure 3 Same as Figure 2 but for Sendai City



Winter (December-January-February)

Weather chart at 00UTC, 10 December 2012

Figure 4 Weather chart for 00UTC on 10 December 2012
The Siberian High developed over the Eurasian Continent and the Aleutian Low developed over the northern North Pacific. Cold air flowed southeastward across Japan, bringing heavy snowfall to its Sea of Japan side.

In winter (December-January-February), the Siberian High develops over the Eurasian Continent and the Aleutian Low develops over the northern North Pacific. Prevailing northwesterly winds cause the advection of cold air from Siberia to Tohoku and bring heavy snowfall to the Sea of Japan side of Tohoku (upstream of mountainous land) and sunny weather to the Pacific side (downstream of mountainous land).

Spring (March-April-May)

Weather chart at 00UTC, 4 May 2006

Figure 5 Weather chart for 00UTC on 4 May 2006
An anticyclonic system covered Japan and brought sunny conditions to northern and eastern Japan.

In spring (March-April-May), migratory cyclones and anticyclones that alternately move eastward prevail across Japan. Temperature increases (decreases) in front (back) of cyclonic systems due to warm southerly (cold northerly) flow. Temperature in Tohoku rises gradually with large short-term variations. The sunshine duration is the longest in the second half of spring due to the predominance of anticyclonic systems.

Summer (June-July-August)

Weather chart at 00UTC, 20 July 2012

Figure 6 Weather chart for 00UTC on 20 July 2012
The Okhotsk High appeared over the Sea of Okhotsk, bringing cool moist easterly winds (called Yamase) to the Pacific side of northern and eastern Japan.

The period from the middle of June to late July is the rainy season (called the Baiu). Its precipitation is caused by a stationary front, called the Baiu front, which forms where a warm maritime tropical air mass meets a cool polar maritime air mass. In the second half of summer, the North Pacific High extends northwestward around Japan, bringing hot and sunny conditions to Tohoku. The Okhotsk High sometimes appears over the Sea of Okhotsk. This causes cool moist easterly winds (called Yamase), which bring cloudy and rainy conditions to the Pacific side of Tohoku.

Autumn (September-October-November)

Weather chart at 00UTC, 11 September 2010

Figure 7 Weather chart for 00UTC on 11 September 2010
Due in part to moist southwesterly flow along the periphery of the Pacific High, the active autumnal rain front brought torrential rain to the Sea of Japan side of Tohoku.

In autumn (September-October-November), temperatures in Tohoku fall gradually. Monthly precipitation amounts over the Pacific side of Tohoku are the largest in September due to the active autumnal rain front and tropical cyclones. In October, the frequent passage of anticyclonic systems brings sunny conditions and refreshing air to Tohoku. The frequency of cold northwesterly flows across Japan and precipitation (rainfall or snowfall) on the Sea of Japan side of Tohoku show an increasing tendency in November.