In complex terrain, the topographic condition has a main role in minimum temperatures. In these areas, radiative inversion occurs in mountain and produces radiative freezing. During nights, the heights cool down as a result of long wavelength radiation, and the cold air near the earth moves towards the bottom of the slope because of its weight. This kind of flow is called the katabolic flow which cause the ice pits to form. [1] Based on the radiation laws, the amount of the long wavelength radiation from the surface of the earth can be calculated at each point considering its characteristics. Meanwhile, employing the digital elevation model (DEM), the modeling of convection flow motion can be achieved. Finally, having the valley\\\\\\\'s properties obtained from the nearest weather forecast station, the amount of temperature decrease in valleys and mountainous regions can be calculated. In this study, a model was developed to quantify the amount of temperature drop and to predict the minimum temperature in order to draw the minimum isothermal graph. Results from this model were compared with the measured data in Darband\\\\\\\'s heights (north of Tehran).these results clearly demonstrated the gradient of minimum temperature in this region.

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