In this paper, the heights of PBL are estimated during daytime (12:00 UTZ) and nighttime (00:00 UTZ) or equivalently 14:00 and 02:00 LST respectively, for a coastal location, Dhahran, in the Kingdom of Saudi Arabia using the potential temperature profiles. These profiles are obtained from radiosonde launches for a period of six years between 1986 and 1991. The monthly average values of PBL height show a seasonal variation during daytime. These variations in PBL height have a great impact on wireless communication, radar performance, and quality of air. Moreover, a prior information on the seasonal trend of this important parameter can be used for site selection of industries, power plants, desalination plants, etc.