National Geographic : 1897 Mar
STORMS AND WEATHER FORECASTS The three conditions essential to the formation of tornadoes are clearly as follows: (1) A cyclone or area of low pressure, the center of which is to the north or northwest, with a barometric pressure not necessarily much below the normal; (2) a tempera ture of about 70 degrees on the morning map; (3) a great hu midity, and (4) that the time of year be March 15 to June 15. These conditions may and often do exist separately; one or two of them may be found coexisting; but so long as the third is ab sent, tornadic formation is not likely to occur. I am satisfied that the number of these storms is not increas ing; that the breaking of the virgin soil, the planting or cutting away of forests, the drainage of land surfaces by tiles, the string ing of thousands of miles of wire, or the laying of iron or steel rails have not materially altered the climatic conditions or con tributed to the frequency or intensity of tornadoes. As well might one by the casting of a pebble attempt to dam the mighty waters of the majestic Mississippi as attempt the modification or restriction by the feeble efforts of man of those tremendous forces of nature which surround our earth and control our storms and climate. To be sure, as towns become more numerous and population becomes more dense, greater destruction will ensue from. the same number of storms. It is not possible with our present knowledge of the mechan ism of storms to forewarn the exact cities and towns that will be visited by tornadoes without alarming some towns that will wholly escape injury; but we know that tornadoes are almost entirely confined to the southeastern quadrant of the cyclone, and that when the thermal, hygrometric, and other conditions are favorable, the spot 300 to 500 miles southeast from the cyclonic center is in the greatest danger. Chart XV shows the conditions on the evening of the St Louis tornado, two hours after its occurrence. The abnormal heat, humidity, and other conditions of the rather small and weak cyclonic system shown by the morning chart were sufficient to justify the Weather Bureau in distributing at 10 a. m. danger warnings throughout the whole of Missouri and eastern Kansas. I am informed that the schools of St Louis were dismissed at once on the receipt of the warning forecast. What is urgently needed is a system by which weather signals may be sent simul taneously from telephone headquarters to all subscribers by a stroke of a telegraph key; then a whole city could be warned in a minute's time.