南北方向の縦谷内低地における暖候季の気温分布特性を明らかにするため、岩手県西和賀地域を対象に7地点の観測点を設置し、1996年6月から9月の期間に気温観測を実施した。アメダス湯田観測点のデータも合わせ分析した結果、当該縦谷には、日較差の平均値が9℃を超える区域(日中に高温、静穏晴夜に低温)をはじめ、多様な気温特性を有する区域が識別された。このような気温分布特性には、縦谷内低地の標高差や谷方位・谷幅等の地形条件が深く関連していることが確認され、特に、谷幅200～300mの峡谷部は、静穏晴夜における気温分布を強く規定していた。Observation of air temperatures was performed during the warm season in 1996 in the Nishiwaga valley in the Ou Backbone Range. Its length runs in the same direction (N-S) as the range and is about 30 km long. The valley-width narrows to 200 and 300 m at two gorges respectively. The results revealed a variety of temperature characteristics in the elongated valley floor. Between upstream and downstream reaches, the difference in the maximum daily temperature was about 2 degrees on average. The main factors that caused this difference are altitude and the width and direction of the valley floor, which influence solar radiation. In addition, the downstream reach has a characteristic climate with a high maximum daily temperature and a low minimum daily temperature. The diurnal range of temperature results exceeded 9 degrees on average. An analysis of potential temperatures detected another reach besides the downstream reach in which cold air is apt to accumulate under calm conditions at night. These reaches lie just upstream of gorges respectively, where cold-air drainage flow in the valley stagnates at night.