Abstract
An investigation was made on the regionality of the seasonal weather changes from autumn to early winter in the Tohoku District.
Average cloud amounts for five-day intervals were used to make a comparison on three pairs of stations on both seacoasts in the district. The seasonal changes of three sections were also investigated with regards to the west-east distributions of average precipitation for five-day intervals as well as the frequencies. The main results are as follows:
1) At the beginning of October the cloud amounts at the Japan Sea side stations get larger than those at the Pacific side stations. This tendency increases towards winter.
2) The situation, in which the Japan Sea side recives rainfalls more frequently and in a larger amount than the Pacific side, makes its start at the middle of October: apparently the winter-type weather contrast between both sides of the Tohoku District begins so early, even in middle autumn.
3) The Japan Sea side rainy (snowy) weather is temporally stopped by a singular period, in which the singularity of November 3rd is included. After this period, the weather condition of the region becomes rainy (snowy) more and more.
4) There is almost no north-south difference of Japan Sea side in the average daily precipitation on the rainy (snowy) days for five-day intervals during the latter half of October. But after the singular period a difference is recognized: the value is higher in the south. Consequently rainfalls during the former term is different from the latter term depending on the area and the cause.
