Senate Document 84 Message from the President of the United States Transmitting A Report of the Secretary of Agriculture in Relation to the Forests, Rivers, and Mountains of the Southern Appalachian Region

The climate of the southern Appalachian region possesses some distinctive features, yet, on the whole, it is rather closely related to the great continental type of the middle latitudes. The pure type of continental climate—cold winters and hot summers—is found immediately to the westward in the Mississippi Valley and the plains region beyond, up to the foothills of the Rocky Mountains. The Atlantic slope has a climate somewhat less severe than that of the interior valleys, being oftener under the influence of warm southerly winds in winter and cooling oceanic winds in summer.

Climatic conditions vary with topographic features.

Intermediate in geographic position between the two great areas just mentioned the southern Appalachian region naturally possesses a climate that partakes somewhat of the main features of the climatic zones both to the westward and the eastward. Its distinctive features are lower temperature, both summer and winter, a drier atmosphere, greater rainfall and snowfall, higher wind velocity, and a greater intensity of the direct solar rays. These characteristics are due for the most part to the greater altitude of the Appalachian region as compared with surrounding levels. In a region of such extremely varied topography there must naturally be limited areas in which, owing to some natural advantage of position or exposure, the climatic conditions are materially different from those which obtain over the greater part of the region. Thus, for example, a mountain slope or a valley facing southward would naturally possess a higher temperature and an immunity from frost not to be found in similar orographic conditions with a northern exposure.

Temperature.

The temperature of the region as a whole can not well be stated, since it is in general proportional to the altitude and is always higher on southern than on northern slopes. Few meteorological observations of any character whatsoever have been made except in the valleys and lower levels; indeed, with the exception of a few months' observations on the summit of Mount Mitchell, no meteorological observations are available for the 4,000-foot level and but two series of observations for the level between 3,000 and 4,000 feet.

The monthly means and extremes of temperature, to which reference will again be made, are given for a number of stations in the tables which accompany this paper.

Winds and weather types.

The wind system of the southern Appalachians in spring, fall, and winter is largely conditioned by the movement in latitude of cyclonic and anticyclonic storms. In the summer season these disturbances move across the country so far to the northward that their influence upon the weather of the southern Appalachians is almost inappreciable. The winds of summer will depend very largely upon the contour of the country, being upward from the valleys along the mountain side during the day and downward at night, with a general westerly drift over the mountain summits. In the more boisterous circulation of spring, late fall, and winter the winds are almost wholly controlled by the atmospheric disturbances passing eastward over the lake region or northeastward from the Gulf of Mexico.

The movement of cyclonic storms eastward across the lake region produces a type of weather in the southern Appalachians which, for convenience, may be called the southwest type. The chief characteristics of this type are southwesterly winds with rising temperature and increasing cloudiness. The velocity of the wind generally increases for a day or so, and finally shifts to the west and northwest, with lower temperature, but not much rain. The southwest is the most common type experienced, and is often associated with long periods of fair, dry weather.

Next in point of frequency to the southwest type is what may be called the west gulf type, from the fact that the weather with which it is associated is produced by storms which approach from the west Gulf States. In this type fresh to brisk southeast to east winds are experienced with generally heavy rain throughout the entire region. As soon as the storm passes the winds shift to a westerly quarter, with markedly cooler weather and frequently snow on the higher summits in winter.

A third type of weather may be mentioned, viz, a type produced by storms which move from the Gulf of Mexico or the West Indies northeastward along the Atlantic coast. In this type strong northeast to north winds prevail. The rainfall, especially in the warm season, is often torrential, and in spring and autumn may continue for several days in succession. In winter such storms are attended by heavy snow and followed by very cold weather.

Weather conditions at high levels.

In 1873 a party of Signal Service observers spent the months of May, June, July, and August on the summit of Mount Mitchell, North Carolina, carefully observing the temperature, rainfall, barometric pressure, and other features of the weather.

The highest temperature observed on the summit of the mountain during the four months was 72° in July; the lowest, 41° in June. The monthly mean temperatures for the four months were as follows: May, 49.3°; June, 54.1°; July, 56.4°, and August, 55.3°. The rainfall was very heavy, 36.8 inches being recorded while the observers were on the summit. Rain fell on 21 days in May, 22 in June, 15 in July, and 21 in August. There was a great abundance of foggy and cloudy weather, the fog and clouds being frequently below the summit. The prevailing winds were from a westerly quarter.

A summary of meteorological observations in the southern Appalachian region appears in the tables which accompany this paper. The highest point at which observations have been made is at Highlands, N. C., elevation 3,817 feet. The mean temperature of summer at that station is 65.7° of winter, 35.4° The extremes reached during a period of eight years, 1893-1900, were 19° below zero in February, 1899, and 86° above zero in June, 1895. The temperature has not reached 90° at that station or at Linville, N. C., the next highest station, altitude 3,800 feet, during the period of observations.

Rainfall.

The precipitation on the southern slopes of the Blue Ridge and connecting spurs is the heaviest in the United States with the exception of the north Pacific coast. It ranges from about 60 inches in northern Georgia to 70 inches in western North Carolina, whence it diminishes northward, falling as low as 40 inches in the southwestern part of Virginia and to almost that figure locally in several portions of the intermediate region. The rainfall of the western slope of the Appalachians in considerably less than on the summits and along the eastern and southern flanks of the mountains, though it generally averages from 40 to 50 inches annually on the lower levels.

As previously stated, the rainfall in the southern Appalachian region is occasionally torrential in character. The mountain ranges of western North Carolina and northern Georgia are so situated with respect to the rain-bearing winds as to greatly facilitate the rapid condensation of moisture, whether borne by the winds from the Gulf of Mexico or the Atlantic Ocean. The indraft of warm, moist air from these great storehouses of moisture and the subsequent cooling as it is forced up the mountain sides give downpours of rain seldom experienced in the adjacent lowlands. On September 22, 1898, 7.57 inches of rain fell within 24 hours at Linville, 6 inches at Lenoir, 8.30 inches at Paterson, 6.75 inches at Marion, and 5.75 inches at Flat Rock. During August, 1901, the total rainfall for the month at Flat Rock was 30 inches; at Highlands, 30 inches; at Hendersonville, 26 inches; at Horse Cove, 26 inches; at Paterson, 24 inches, and at Marion, 21 inches. The precipitation for the year 1898 in western North Carolina at Highlands was 105.25 inches; at Horse Cove, 99.97 inches; Flat Rock, 78.39 inches, and Linville, 71.05 inches. These heavy downpours naturally cause destructive floods in the streams whose headwaters penetrate the mountain region. The severity of the floods is in a large measure mitigated by the fact that a large proportion of the rainfall is conserved by the forest covering, which abounds on the greater part of the area, and is thus prevented from reaching the streams quickly and in great volume, as would be the case were the mountain sides and the summits bare. It is a mistake to suppose the forests per se tend to increase precipitation. The precipitation would be equally heavy, forest or no forest. In the latter case it would run off more quickly and the regimen of the streams would be much more irregular than in the case of a forested area.

Not much can be said of the relative humidity of the higher elevations, since no observations have been made. Along the western edge of the Piedmont Plateau the air is considerably drier than on the coastal plain. Tables of monthly mean relative humidity for Atlanta, Ga., Charlotte and Asheville, N. C., and Chattanooga and Knoxville, Tenn., accompany this report, and there have been added, for the sake of comparison, similar data for Savannah, Wilmington, and Raleigh on the east, Montgomery on the south, and Memphis, Nashville, and Cincinnati on the west. The data for Asheville are not directly comparable with those of the remaining stations, since the Asheville observations were made three times daily, viz, at 7 a. m., 2 and 9 p. m., whereas observations at the remaining stations were made but twice daily, viz, at 8 a. m. and 8 p. m. The omission of an observation during the driest part of the day tends to give mean values somewhat above the true figures. Nevertheless, the observations at Asheville confirm the local belief that the relative humidity of the mountain region is less than that of lower levels.

TABLE 1.—Normal monthly mean temperature (in degrees Fahrenheit,) compiled in the Weather Bureau, United States Department of Agriculture, from observations extending over a series of years.

TABLE 2.—Highest temperatures observed during the eight years 1893 to 1900, at the points named; a compiled in the Weather Bureau, United States Department of Agriculture.

TABLE 3.—Lowest temperatures observed during the eight years 1893 to 1900, at the points named; a compiled in the Weather Bureau, United States Department of Agriculture.
[Minus signs indicate temperatures below zero F.]

TABLE 4.—Mean monthly and annual precipitation, in inches and hundredths; compiled in the Weather Bureau, United States Department of Agriculture, from all available records from the beginning of observations to December, 1900.

TABLE 5.—Monthly mean relative humidity, compiled in the Weather Bureau, United States Department of Agriculture.