Abstract
In order to study the geographical distribution of daily snowfall in the Tohoku region and its relation to synoptic weather conditions, the 10 district regions were first identified. All of these areas experience intense snowfall by either one of the three major types of snowfall. The first type of snowfall, defined by Types D, E and F occurs in the mountainous regions with the winter monsoons. The second type, defined by Types A, B and C occurs near Japan Sea coast. Finally the third type which is associated with cyclones is defined by Types G, H, I and J.
The study of synoptic conditions associated with snowfall types has shown distinct conditions for each of the three major types of snowfall. In the case of mountain snowfall, the wind at the 850-mb level over Akita was strong. The mechanism of the coastal snowfall was found to be different between the northern (Types A and B) and the southern (Type C) regions. In the southern regions, the wind at the 850-mb level over Akita was weaker than 10m/sec, but in the northern regions rather stronger. Hence, it can be concluded that the distribution type of snowfall in the southern region is similar to that occurred in the Hokuriku region. On the other hand, the distribution type of the coastal snowfall in the northern region appears to be unique to the Tohoku region. The third major type of snowfall which is associated with cyclones is characterized by the absence of cold air at the 850-mb level. In addition, the regionality of the snowfall occurred under the strong influence of the track of the cyclone.
As a result, each of the 10 region which was defined by the probability of the simul-taneous occurrence of intense-snowfall day, may possess distinct characteristics in addition to the common characteristics associated with one of the three major types of snowfall in the Tohoku region.
