CHAPTER III
THE STORM CYCLE
Doubtless those who hope for a Hereafter of unmitigated ease and song, desire, on this earth, one long, sweet anticyclone. But theirs, in most of the United States, is disappointment. With an irregularity that seems perversely regular at times our fair weather is interrupted by a storm which in turn gives way to some more fair weather or another storm,—there is no telling which very long in advance. And that is why American weather ranks high among our speculative interests.
To emphasize this irregularity a seemingly regular succession of events may be noticed. It will cloud up, let’s say, on a Sunday, rain on Monday and Tuesday, clear on Wednesday, staying clear until Sunday when it will cloud up for the repeat. During this past season it rained on a dozen washdays in succession. The newspapers grew jocular about it. And very often one notices two or three rainy Sundays in a row. By actual observation this year we enjoyed fifteen clear Thursdays in succession in a normal spring.
The weather gets into a rut. And if the anticyclones and cyclones were all of the same intensity it is conceivable that the rainy Sundays might go on until the Day of Rest was changed by Statute. But the intensities of the whirls differ. Before long an anticyclone feebler than ordinary is overtaken by a cyclone and annihilated. Or one stronger than the average may dominate the situation for several days. Or the great body of cold air in winter over the interior of Canada may send a succession of moderate antis across our country making a barrier of dry cold air through which the lurking cyclone can not push.
Mostly, however, three days of anticyclonic influence and three days of cyclonic influence with one day in between for rest, the transition period, make up a normal week of it. Let the American farmer thank his stars (and clouds) for that. For no other regions of the earth are so consistently watered and sunned all the year round as the great expanse of the North American Continent.
The cyclone is that activity of the atmosphere which prevents us from suffering from an eternal drought. The cyclone is an accumulation of air which has become warmer than the air about it. This area of air usually has a central portion that is warmest of all. Since warmth expands, this air grows lighter and rises. Nature, steadfast in her grudge against a vacuum, causes the surrounding air to rush it. Since these contending currents cannot all occupy the central area at once they fall into a vast ascending spiral that spins faster and faster as it approaches the center. Imagine an inverted whirlpool. It is a replica on a much smaller scale of the great polar influx, except that the latter has a descending motion.
The cyclone thus is tails to the anticyclone’s heads, the reverse of the coin. Where the anti’s air was cool and dry the cyclone’s is warm and moist. The anti had a downward tendency and a motion, in our hemisphere, flowing outward from the apex in generous curves in the direction of clock hands. The cyclone has an upward tendency, flowing inward to the core contrariwise to clock hands.
From these two great actions and reactions come all the varieties of our weather. To understand the procession of the cyclones and anticyclones across our plateaus, our mountains, our plains, and our eastern highland is to know why, and often when, it will be clear or not. To mentally visualize the splendid sweep of the elements on their transcontinental run is to glimpse grandeur in the order of things which will go far to offset the petty annoyances of fog or sleet. Ignorance may be bliss, but knowledge is preparedness.