We frequently experience south wind at Utunomiya in the daytime in winter when the NW monsoon should blow. To investigate its mechanism simultaneous observation were made on Feb. 3rd, 1946, at about 30 stations in Totigi Profecture. As a result of the analysis of the data of observations, it was ascertained that the south wind occurrences are caused by the local front of diurnal change. And with the aid of statistical data, a clue, for the forecasting of the gale accompanied by the front was obtained and interpretation of the climate of Totigi Prefecture in winter was given.