CLIMATOLOGY AND HYDROLOGY 



INTRODUCTION 



This section relates information on water availability and its use in 

 coastal Alabama. Included is a description of the coastal climate and how it 

 affects the area, stream and river discharge, and surface and ground water 

 availability and quality. Currents and their effects on salinities in the 

 coastal estuaries are also discussed. 



CLIMATE 



Temperature 



The climate of coastal Alabama is primarily humid subtropical, due to the 

 warming influence of the Gulf of Mexico. This large warm-water surface is a 

 major contributor to warm, humid summers, and mild winters, with a fairly 

 consistent range of temperature extremes (Lineback 1973). 



Coastal Alabama air temperatures are relatively mild, with an average 

 annual temperature in Mobile of 20 °C (68 °F). Mean annual temperature 

 variation is approximately 10 °C (18 °F) (Table 31). Summer temperatures are 

 rarely high ranging between 21 and 32 °C (70 and 90 °F). Temperatures in 

 winter generally range between 4 to 16 °C (40 and 60 °F), with temperatures 

 below freezing occurring on an average of 22 days per year. Periods of 

 freezing temperatures generally do not last more than 2 or 3 days. The 

 lowest mean monthly temperatures, 10 °C (50 °F), occur in January, while July 

 produces the highest average temperatures (28 °C, 82 °F). Temperature 

 extremes in the Mobile area vary from a maximum of 40 °C (104 °F) (July 1952) 

 to a low of -18 °C (-1 °F) (February 1899) (National Climate Center 1980). 



Mobile and Baldwin Counties have a growing season ranging from 230 days 

 in the northern sector to 300 days in areas near the coast. The first 

 killing frost occurs in early November in the northern parts of the counties 

 and early December in areas near the coast. The last killing frost occurs in 

 mid-February near the coast (0 'Neil and Mettee 1982). 



Precipitation 



The normal annual rainfall in coastal Alabama is the highest in the state 

 and among the highest in the United States. Average annual rainfall in the 

 Mobile area is about 162.5 cm (64 inches) (Table 32). Rainfall is fairly 

 evenly distributed throughout the year with a slight maximum at the height of 

 the summer thunderstorm season in July and a slight minimum during the late 

 fall in October. 



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