TOPOGRAPHIC FEATURES – Louisiana lies roughly between latitudes 29.5 and 33 degrees North and from the 94^th meridian eastward to the Mississippi River. Elevations increase gradually from the coast northward, rising to over 100 feet above sea level on uplands and 400 to 500 feet on some of the hills in the northwest. In the north are rolling hills, while in the east many bluffs dot the river plain. Coastal marshes and bayous are features of the southern terrain. The Mississippi Delta, a fertile sedimentary deposit, comprises a third of the State's total area.

Drainage in Louisiana is into the Gulf of Mexico. The Red River basin comprises the largest drainage area in the state. The Red joins with the Atchafalaya and Old Rivers, the latter forming an outlet to the Mississippi River. Most of the water from the Red flows to the Gulf through the Atchafalaya system, except on rare occasions when the Mississippi is at higher stages much of it's flow will be through Old River and then into the Atchafalaya. In times of high water the lower Black basin, near the confluence of the Black and the Red, becomes a backwater storage basin. Because of an extensive artificial levee system there is not much drainage directly into the Mississippi within the state. Lowlands bordering the Red and upper Atchafalaya are also protected by levees.

Southern Louisiana is mostly low and level with elevations generally less than 60 feet above mean Gulf level. The runoff is through numerous sluggish streams or bayous which flow through lakes and considerable marshland. The larger marshlands are mainly in the coastal area, extending farthest inland in the southeast. A great part of the southwestern region is drained through the Calcasieu River. The extreme southwestern part of the state drains into the Sabine River which forms more than half of the western boundary. The Pearl river drains a relatively small area in the southeast and forms the southeastern boundary.

CLIMATIC FEATURES – The principal influences that determine the climate of Louisiana are its subtropical latitude and its proximity to the Gulf of Mexico. The marine tropical influence is evident from the fact that the average water temperature of the Gulf along the Louisiana shore ranges from approximately 64 degrees F in February to 84 degrees F in August. Elevation and type of soil is a factor of varying importance.

In summer the prevailing southerly winds provide moist, semitropical weather often favorable for afternoon thunderstorms. When westerly to northerly winds occur, periods of hotter and drier weather interrupt the prevailing moist condition. In the colder season the state is subjected alternately to tropical air and cold continental air, in periods of varying length. Although warmed by its southward journey, the cold air occasionally brings large and rather sudden drops in temperature, but conditions are usually not severe.

Louisiana is south of the usual track of winter storm centers, but occasionally one moves this far south. In some winters a succession of low pressure centers will develop in the Gulf of Mexico and move over or near the state. The winter of 1957-58 was a classic example. The state is occasionally in the path of tropical storms or hurricanes.

From December to May the water of the Mississippi River is usually colder than the air temperature, which favors river fogs during this season, particularly with weak southerly winds. In the more southern sections, lakes also serve to modify the extremes of temperature and to increase fogginess over narrow strips along the shores.

TEMPERATURE – The average annual temperature ranges from about 66 degrees F in northern divisions to about 69 degrees F in southern divisions. The lowest January average is approximately 49 degrees F in the northwest and north-central ranging upward to 57 degrees F in the southeast. The highest July average is 83 degrees F in the northwest and north-central, ranging downward to 81 degrees F in the east-central (north of Lake Ponchartrain). This reversal of temperature distribution with warmer summers in the northern portion than in the southern portion, is due to the almost daily showers in the parishes near or along the Gulf of Mexico. This is further shown by the number of days with temperatures 90 degrees F or above. While Shreveport and Alexandria average 102 such days, Lake Charles and New Orleans average 86 and 57 , respectively. In other words, at New Orleans, where there is a 50 percent expectancy of showers on any day in July, the temperature reaches or exceeds 90 degrees F about half as often as at Shreveport where summer showers are much less frequent. The highest temperature ever recorded in Louisiana was 114 degrees F on August 10, 1936, at Plain Dealing. The lowest temperature ever recorded in Louisiana was 16 degrees F below zero on February 13, 1899, at Minden. Despite this, temperatures above 100 degrees F and below zero are rare. The average number of days with freezing temperature or lower ranges from 24 in Shreveport to 4 at New Orleans. Near the mouth of the Mississippi River a freeze can be expected only about once in seven years. Growing seasons are long, ranging from 220 days in the north, to over 300 in the southern portion of the state.

PRECIPITATION - Mean annual precipitation ranges from 46 inches in Caddo Parish to as much as 66 inches in parts of St. Mary, Assumption, Terrebone, and Lafourche Parishes. A median line of 56 inches per year runs from Hackberry northward to Leeville, Montgomery, Winona, Luna, and southward to Harrisonburg and Deerpark on the Mississippi River. This line separates areas of lower precipitation averages to the north from areas of higher precipitation to the south.

During the summer months, seasonal rainfall usually increases from the northwest (9 inches) toward the southeast (22 inches). In the winter this pattern is reversed with the heaviest seasonal precipitation 917 inches) in the area extending from the Carroll Parishes southwestward to Winn and southward to St. Landry, with the least (13 inches) in the lower delta. During the summer months the rich source of moist tropical air results in almost daily showers in the coastal parishes; however, shower frequency diminishes with distance from the Gulf Coast toward the northern parishes. In the winter months the northern portion of the state is invaded by cold air which tends to stall and become stationary. This sometimes produces prolonged rains over that area, while clear weather continues in the southern parishes. The pattern of spring rains is similar to that of winter, while fall rains are distributed in the same manner as summer rains. However, fall (September, October, and November) is the driest season of the year, with precipitation ranging from 9 inches in the north to 15 inches in the southeast. Spring precipitation ranges from 13 inches on the coast to 18 inches in the central interior.

The heaviest rains of short duration are associated with thunderstorms, although tropical storms sometimes cause prolonged heavy rains. An example is the august 1940 tropical storm which deposited over 19 inches of rain at Crowley and Lafayette in 24 hours. Aside from this, rains of as much as 20 inches in a month have occurred at most stations, and falls of as much as 10 inches in 24 hours are not rare. Although Louisiana is one of the wettest states, droughts are not unknown, especially during the summer and fall. For instance, in New Orleans, where the normal annual precipitation is 63.54 inches, in each decade since 1870, there has been one or more periods of 3 consecutive weeks without measurable rainfall. The longest such period in 87 years of record was 52 days, from September 29 to November 11, 1924.

The heaviest recorded rate of rainfall was 1 inch in 5 minutes at New Orleans during the thunderstorm of February 5, 1955. This is a rate of 12 inches per hour. However, such a rate of fall is never long sustained and, in fact, in 1 hour this storm produced only 2.37 inches.

Showers and thunderstorms occur on an average of 50 to 60 days a year in the northwest and north-central, 70 days in central and northeast Louisiana. During fall, winter, and spring, these are often attended by high winds, but this is no the case during the summer. Thunderstorms which move off Lake Ponchartrain at any season are usually attended by high winds. During late fall, winter, and early spring, thunder may occur at any time of the day, but from late spring to early fall about 80 percent of all thunderstorms occur between noon and midnight in the northern and between 6 am. And 6 pm. In the southern half of the state.

Snow and sleet are of little importance in Louisiana except for rare storms that have dumped up to 24 inches at some stations. Significant snow storms have occurred in the month of February in 1895, 1899, and 1973.

FLOODS – Flood-producing rains may occur during any month of the year in Louisiana, although they are less likely during September, October, and November, the drier months, and are most frequent during late winter and early spring. Floods on the lower Mississippi and Atchafalaya result from runoff upstream, and rainfall within the state has little influence on these stages. The flow of the Red River is controlled by Denison Dam at Denison, Texas. Also, discharge into the Red from the sulphur River, as important western tributary, is controlled by Texarcana Dam. Major floods can still occur on the lower Red River from heavy rains in Louisiana.

Heavy rains cause several minor floods each year on the Sabine, Calcasieu, and Mermentau Rivers. A major flood on the Sabine occurs about once in 4 years. In th upper portions of the Calcasieu and Mermentau a major flood occurs about once in 10 years and in the lower portions not more than once in 25 years. The Mississippi and Atchafalaya Rivers have a record of a major flood every 2 years, but due to flood control systems (levees and floodways) the resultant damage is relatively minor. Major floods on the lower Mis River average about 6 years apart.

STORMS AND OTHER WEATHER – Tropical storms and hurricanes are a potential hazard to life and property in Louisiana, especially along the coast. The records show that such storms are experienced in the state on the average of about once a year. Of course, not all tropical storms reach hurricane intensity (wind speeds > 74 miles per hour), but even gale winds can be destructive. Although these storms can occur from June through November, September is the month of greatest frequency. Tornadoes can strike in any month and occur somewhere in the state almost every year. The greatest number of tornadoes reported in a single year was 55 (1974), while the fewest was 5. Most occur in the months of February to May, and November. It should be noted that hurricane and tornadoes affect only a relatively small area for a brief time and their frequency is really quite low. Contrasting with these occasional adverse features are the mild and short winters, abundant precipitation, and the long growing (frost-free) season.

AGRICULTURE AND RECREATION – Louisiana agriculture is well adapted to climatic influences, with many crops grown in fairly well defined regions. Cotton is grown primarily in the northern and central districts where summer rainfall is generally insufficient for other crops, while rice is grown on the flat prairie lands of the southwest with its plentiful water supply. Sugar cane is grown primarily in the south-central, the western portion of the southeast, and the southern portion of the central district, where copious rainfall and a long growing season are nearly ideal. Citrus fruits are grown in a narrow strip bordering the Mississippi River below New Orleans, where freezes occur about once in 7 years, on the average. Tung culture is practiced n Washington, and St. Tammary Parishes, but it is still doubtful that the climate of the area favors this in other than exceptional years. The rapidly growing industrialization of Louisiana, especially in the southern third of the state, is no doubt partly due to the favorable climate and unfailing water supply. The chief industries consist of chemical, petroleum, sulfur, aluminum, paper, shipping, fishing, trapping, and winter tourist trade. Construction is carried on throughout the year. The “frost line” offers no problem as freezes are usually of 1 to 3 days duration, and freezing of the soil is rare even in the northern parishes.

Outdoor recreational activities are possible for a longer period of the year than in the Northern States. Golfing is a year-round activity, but swimming is confined to the warmer half of the year even on the coast. Tourism has become a major enterprise and the state offers many historical attractions. The famed French Quarter and Mardi Gras Festival of New Orleans are known around the world.

Adapted from: Climatography of the United States No. 60, National Climatic Center