Physical Environments - Climate Contributor: Kindinger
Climate is integral to the natural systems of Pontchartrain Basin. Short- and long-term climate variability has an enormous impact on the seasonal and long-term health of any ecosystem.
Annual average temperatures range from 19 to 21°C (66 to 69°F) , with July averaging 28°C (82°F) and January averaging 12°C (53°F).
Snow rarely falls in the southern sections, with only small snowfalls usually recorded in the northern areas. The statewide annual rainfall is about 142 cm (56 in) a year, with the northern regions averaging 117 cm (46 in) and some of the southern coastal parishes averaging as high as 167 cm (66 in) of rainfall a year.
The climate of the New Orleans area can has been described by Ruffner and Bair (1977) as humid with the surrounding water modifying the temperature and decreasing the range between the extremes. Almost daily sporadic afternoon thunderstorms from mid-June through September keep the temperature from rising much above 30°C (90°F). There is only an average of about seven days per year when the temperature reaches 35°C (95°F). From about mid-November to mid-March, the area is subjected alternately to the southerly flow of warm tropical air and to the northerly flow of cold continental air in periods of varying lengths. The usual track of winter storms is to the north of New Orleans, but occasionally one moves this far south, bringing large and rather sudden drops in temperature. However, the cold spells seldom last over three or four days.
During the winter and spring, the cold Mississippi River water enhances the formation of river fogs, particularly when light southerly winds bring warm moist air into the area from the Gulf of Mexico. The nearby lakes and marshes also contribute to fog formation. Even so, the fog usually does not seriously affect automobile traffic except for brief periods.
Rather frequent and sometimes very heavy rains are typical for this area. During the past 100 years, an average of 120 days of measurable rain per year occurred at the official observation site in the city with the annual amount averaging 153.5 cm (60.44 in).
A fairly definite rainy period is from mid-December to mid-March. Precipitation during this period is most likely to be steady rain. May, October and November are generally dry, but there have been some extremely heavy showers in those months.
While thunder occurs with most of the showers in the area, thunderstorms with damaging winds are infrequent. Hail of a damaging nature seldom occurs, and tornadoes are extremely rare. However, waterspouts are observed quite often on nearby lakes.
Specific climate data for several regions around Lake Pontchartrain are shown in the following pages.
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