A strong local wind has been observed in Rumoi, northwestern Hokkaido, Japan. In order to investigate the wind around Rumoi, an analysis was performed using 30-year AMeDAS wind observations and numerical experiments with the Weather Research and Forecasting (WRF) model. Observation results show that there is a frequent strong wind in Rumoi in comparison with other areas around Rumoi. In relation to seasonal changes in wind direction, more than 50% of the wind in summer blows from ESE, but westerly winds are frequent in winter. To clarify the mechanisms involved in producing a strong local wind in winter, we compared two events using observations and numerical experiments. One case involves a strong local wind with a speed of approximately 12 m/s in Rumoi and a weak wind of less than 5 m/s in the surrounding areas; the prevailing wind direction is ESE (03:00 on January 28, 2003). The other case is that of a strong wind over 10 m/s blowing over the entire study area (on the afternoon of March 8, 2005), with a westerly prevailing wind. The experimental results show a relatively good correspondence with those of the observation. A cross-section view demonstrates the existence of a mountain wave when the strong local wind is observed in Rumoi. The wind then passes through the valleyshaped topography, and wind speeds are accelerated in the vicinity of Rumoi, which suggests the existence of a gap wind. Additionally, a sensitivity experiment is performed by changing the land surface model without considering snow, and the wind speed over land is seen to be reduced by 2 m/s, with very little change in the wind direction.