Weather refers to the state of atmosphere at any given time denoting the short term variations of atmosphere in terms of temperature, pressure, wind, moisture, cloudiness, precipitation, and visibility. It is highly variable and changing constantly, sometimes from hour to hour and at other times from day to day. The afore- mentioned properties of the atmosphere are subject to constant change, and their state at any time determines the state of the weather. However, weather elements are not separate entities; rather they are closely related with each other. According to David l. Blumenstock, an eminent climatologist, "weather is the behavior of the lower atmosphere with particular emphasis on those aspects affecting the land and water of the earth". For the environmental scientist and geographer, this definition of weather is more satisfactory (Lal, 2000).
Weather has been described as the sum total of atmospheric condition for any place for a short period of time. The weather elements include atmospheric pressure, temperature, winds, humidity and precipitation (Gates, 1972).Weather affects particularly all aspects of our lives. The air we breathe must be clean and not to be polluted. In our homes, we want a steady temperature and a comfortable humidity (Bodin, 1978). The weather includes all daily changes in temperature, wind, moisture and air pressure .It plays an important part in many human activities. Farmers need a good weather so that the crops are not destroyed. Strom and frost can destroy the valuable crops .Transportation and communication also are affected by bad weather .Fog often affects aviation, transportation and navigation. Therefore, weather forecasting plays a vital role and developed countries invest much in this field (Encyclopedia).