Jacques Wardlaw Redway

“ The tornado is a whirling storm, and the whirl becomes so rapid that the vortex develops into a black funnel-cloud. The funnel is usually observed first in the air. As the whirl increases, the funnel gradually extends downward to the ground. No measured velocity of the whirl is known to have been made; but calculations based on the weight and the surface of bodies moved by the wind show that the velocity, in various instances, has exceeded 500 miles per hour. ”

“ Not only may a cyclonic storm swerve from its predicted track; it also may fail to produce the rain or the snow which, according to popular tradition, constitutes the storm. As a matter of fact, the rain and the snow are merely an incident in a cyclonic movement. The essential feature of cyclone mechanics is the updraught. Now, in its progress if the cyclone invades an area of very dry air, the updraught may not be cooled to the temperature of condensation; in such a case there will be no precipitation. All lows are not rain storms or snow storms in the ordinary meaning ”

“ The position of the storm center may be determined by watching the wind closely and noting any change that may occur. Standing with the back to the wind the area of low pressure is on the left hand, and the area of high pressure on the right hand. During the passage of the storm, if the wind shifts from the east through north to northwest—that is, if it “backs in”—the cyclone center is passing to the south of the observer. If it veers through the south to the west or the northwest, the storm center is passing north of the observer. ”

“ The cooperative observer can do much to aid in establishing definite facts on which predictions may be made. Among them and of first importance is establishment of the direction of rain-winds. These, as has been shown, are easterly winds, but conditions of topography may change the real direction to one that is apparent. The apparent direction should be established for each month in the year. In every community there are weather-wise people who possess valuable information that they have not recorded. ”

“ Just as the trough of a wave is followed by a crest, so a low is pretty apt to be followed by a high; and cyclonic storms of the Alberta type are frequently followed by crests or waves of cold air from high latitudes. ”

“ The low of the West Indian hurricanes is very much smaller in area. Even after its existence has been discovered it may not be more than 100 miles in diameter; and by the time it passes a West Indian weather station it may not be more than 200 or 300 miles across. After it recurves and enters the United States, its area is much less than that of the ordinary cyclonic storm; the isobars are usually regular and more nearly of circular shape than those of ordinary storms. ”

“ Now, if the heavier cold air rests at the surface of the earth no disturbance follows. On the other hand, if the cold air comes to rest on the top of a thick layer of warm air, an unstable condition results. Sooner or later an updraught of warm air takes place and tornado conditions are established. ”

“ Almost every daily paper publishes a résumé of the weather map; some reproduce the map itself. All told, the daily forecast is so widely published that it is within almost instant reach of everyone within the main body of the country. ”

“ Inasmuch as the storm tracks of the different types are fairly regular in position, and the velocity of progress is known, it is not difficult to forecast the position of a storm from day to day; that is, a storm center which is over Cincinnati may be expected to reach Philadelphia or New York at about the same hour on the following day. Fast express trains run at a rate of speed that rarely varies; the cyclonic storm moves also at a fairly uniform speed. The express train does not ordinarily leave its steel-bound track ”

“ When the spout breaks, a considerable part of the water in the air drops in a torrential deluge. Popular tradition has it that sea water drawn into a spout falls as fresh water—a tradition that is contrary to the facts of the case. ”

“ The rapid whirl creates a near- vacuum, and this accounts for the fact that buildings struck bv the funnel-cloud burst outwardly. The air movement of tornadoes is three-fold—the updraught, the whirl, and the progressive movement. The destructive path of the tornado is as wide as the funnel-cloud, rarely more than a few rods. The entire whirl is not much more than half a mile in diameter; the extent of the path varies from a few miles to about 200 miles. The tornado progresses along its track at a rate varying from 10 or 12 miles an hour to express-train speed. ”

“ From the nature of the case, the best values concerning the dynamic force of the tornado are only approximate, but even these are instructive. Normal air pressure is at the rate of 2117 pounds per square foot. Now, if the air pressure within the funnel is only three-fourths normal when the funnel involves a building, the air pressure inside the building will be 530 pounds per square foot greater than on the outside. Such a difference in pressure is sufficient to burst the walls of almost any building. ”

“ They are more common in the United States than in Europe. The regions of greatest frequency are the lower Ohio and Missouri valleys and the Central Mississippi region. Very few occur in the arid region west of the one-hundredth meridian and fewer still are reported north of the fiftieth parallel. ”