Observational study was made of the thermal belt during December 19-20, 2002, in the western slope of Mt. Tsukuba, central Japan. Using a spatially distributed temperature logger, 1.5 m above the land surface, it was revealed that the maximum temperature is centered around 200 ∼ 250 m above sea level (a.s.l.), especially developing in the early morning. The vertical temperature profile was observed by use of captive balloons. Strong surface inversion, in excess of 4°C, occurred in the bottom of the mountain around daybreak, while the vertical distribution of temperature at 150 m a.s.l. is uniform, roughly 3.5°C ∼ 4.5°C, up to 40 m from the terrain. The time series of air temperature toward daybreak implicates a significant role of radiation cooling, since the abrupt temperature fall was concurrent with rapid improvement of weather. Analysis of thermal image, obtained by thermography, also indicates that this relatively warmer region extends in the mid-slope of the mountain. However, zonally nonuniform temperature distributions implicate a presence of terrain-related cold air drainage.