Air temperature and sunshine duration for agricultural fields were extracted from 1‐km‐resolution weather data, and their relationship with winter wheat yield was compared for the adjacent Tokachi and Okhotsk regions of eastern Hokkaido, Japan. Major climatic drivers of winter wheat yield were air temperature during spring and grain‐filling period in Tokachi, and sunshine duration during grain‐filling period in Okhotsk. The regional difference in the sensitivity of yield to air temperature is attributed to variations in sunshine duration during grain‐filling period. In Tokachi, a shorter grain‐filling period limits the cumulative sunlight available to plants, because sunshine duration declines from late June to late July. In Okhotsk, yields of winter wheat were attributed to receiving adequate sunlight, although the growth period was curtailed by higher air temperature. We found that different climatic drivers affected winter wheat yield even in adjacent regions. The sensitivity of winter wheat yield to temperature can be determined by a threshold of 4.5 h daily sunshine duration regardless of region. Short sunshine duration during the grain‐filling period exacerbated the sensitivity of wheat yield to temperature. Early summer in Okhotsk is characterized by sunnier weather than in Tokachi due to foehn, with respect to the southerly winds. Then, southerly wind was associated with significantly longer sunshine duration in Okhotsk. Regional cloud development affects sunshine duration as the climatic driver of wheat yield.