[Illustration: FIG. 19.—THE ST. LOUIS TORNADO OF MAY 27, 1896, SHOT A SHOVEL SIX INCHES INTO THE BODY OF A TREE.] Some have advocated the planting of trees to the southwest of cities in the regions where tornadoes are frequent, so that the tornadoes may expend their energy in uprooting the trees before they come to the city, but this storm traveled through several miles of brick buildings, razing them to the ground and almost pulverizing them and still left the city apparently with greater force than it had on entering. The largest trees would offer no more resistance to a tornado cloud than would so many blades of grass. When the official forecasts contain the statement that conditions are favorable for “severe local storms” it would be well to carefully observe the formation of portentous clouds in the west and southwest, between 3 and 6 o’clock in the afternoon, and if one with black, ragged fringes on its lower edge and accompanied with a noise like several railroad trains makes its appearance, seek safety in the cellar of a frame house. [Illustration: FIG. 20.—THE ST. LOUIS TORNADO DROVE STRAWS ONE HALF INCH INTO WOOD.] =General Rules for Forecastings.= What has gone before in this chapter gives an idea of what guides the weather forecaster in making his deductions. In brief, he studies the developments and the movements of the Highs and the Lows during the past two or three days, as shown by preceding weather maps, and from the knowledge gained forecasts the future course and intensity of the fair and the foul weather areas for one, two, or three days in advance. By preserving the weather map each day and noting the movements of the Highs and the Lows, any intelligent person can make a fairly accurate forecast for himself, always remembering that the Lows, as they drift towards him, will bring warmer weather and sometimes rain or snow, and that as they pass his place of observation the Highs following in the tracks of the Lows will bring cooler and fair weather, except during periods of extreme summer heat, when the Lows bring showers that cool the parched earth; and except in the north Rocky Mountain plateau, where most of the precipitation occurs after the center of the Low has passed and northwest winds are blowing. The amateur weather forecaster can closely anticipate the temperature of his region by remembering that the weather will be cool and the humidity low so long as the center of the predominating High (the High inclosing the greatest area within the thirty-inch isobar) is north of his latitude, either northeast or northwest, and that it will be warm so long as the High is south of the parallel of latitude that passes through his section of country.