The heavy but fairly well-distributed rains of May and June, accompanied by moderate temperatures, induced a remarkably vigorous growth of vegetation; and wheat, oats, and corn devel oped rapidly. The continuance of excessive rains through July and August made the harvesting and threshing of wheat and oats very difficult. Even with these handicaps of weather a most satisfactory yield was procured and marketed.
The excess of rainfall for August was due almost wholly to the passage of the Galveston hurricane diagonally across the state from southwest to northeast, August 17-18, with exceed ingly heavy rainfall, some points reporting more than 8 inches. This excessive rainfall and the high winds accompanying it laid the ripening corn over vast areas flat on the muddy ground. The moderate rainfall of September, however, followed by a clear and dry October and November, permitted the successful ripening and harvesting of an abundant corn crop.
The heavy rains of the year and their peculiar distribution in some localities were so far removed from the ordinary as to make perceptible changes in the annual-rainfall map of the state when the 1915 reports were averaged with all preceding records.
Tornadoes.—Many tornadoes have occurred in Illinois, and have done great damage over small areas. The tornado is a small, violent, whirling storm, which sometimes develops in the southeast quadrant of a cyclone, or low-pressure area, during the spring and summer months. It is almost always less than a mile, often only a few hundred feet, in width. Its course is easterly and the path is usually 20 or 30 miles in length. Tornadoes are more common in the Mississippi Basin than else where in the world. The St. Louis tornado of May 27, 1896, caused its greatest destruction in the city of St. Louis, but the storm crossed the Mississippi River and did much damage in Illinois. No means has been found for forecasting the time or place of occurrence of a tornado. In the open country a person may observe the narrow, funnel-shaped cloud approaching and run out of its path so as to escape its violence. It is better to run to the north of the center of the path as the winds are less violent on the north than on the south side of the tornado.
On May 26, 1917, Illinois and Indiana experienced two of the most remarkable tornadoes in the history of the Weather Bureau observations. These storms are fully described in the
Weather Bureau reports for May, 1917. Only a brief summary can be given here: Sleet, hail, and ice storms.—Precipitation sometimes falls in winter in the form of small, clear pellets of ice consisting of frozen raindrops known as sleet. Sleet is also called "winter hail." Small, white pellets of compacted snow occasionally fall in spring or late autumn. This is sometimes called "soft hail," but the Weather Bureau reports it only as snow.
Hail sometimes falls during a thunderstorm. It accom panies thunderstorms in the hottest part of the year and the hottest part of the day. The area receiving hail is smaller than the area of the accompanying thunderstorm. A large hail storm may be 6 to 7 miles wide and 40 to 50 miles long. Hail stones vary in size up to several inches in diameter. Doubtless hail has fallen in every part of Illinois. In some instances the destruction caused has been very great. Cornstalks have been stripped of their leaves and the crop practically ruined. Windows of houses have been broken, and the glass coverings of greenhouses have been shattered. In some cases animals have been killed.
The Weather Bureau report of June, 1915, gives an account of a destructive hailstorm which occurred during the night of June 20-21. The hailstorm crossed the state in a southeasterly direction from Calhoun County, where it appeared at S.30 P.M., to Wabash County, where it passed into Indiana about mid night.
Buildings and trees were destroyed, wire service crippled, trains delayed one person injured, large quantities of plate glass in store windows and glass in greenhouses broken by hail; timothy, oats, corn, and wheat laid flat by the wind and torn into shreds by the hail, causing a loss to crops alone of thousands of dollars. White County reports the total damage to buildings and crops as approximately $100,000. Carrollton, Greene County, reports an estimated loss in that immediate vicinity of more than $100,000. The hail killed 50 shoats on a farm near Carrollton. Reports stated also that some sheep and cows were killed by the hail.