"So does air," the Forecaster rejoined. "There is something the same sort of a whirl at the poles. The prevailing westerly winds of the United States are due to this circumpolar whirl, though modified and altered by the changes of the seasons, the differences of heat between day and night, the radiation from the land, the irregularity of the coastline, the currents of the ocean and a thousand other factors. Each of these the Weather Man has to study when he makes a forecast, but, in the United States, his work is aided by the fact that weather always travels eastward and that the storm follows regular tracks, sharply outlined, like Indian trails across the country." "Roads in the air?" queried Fred. "Yes, my boy," the Forecaster answered, "regular roads in the air. There used to be an old saying: 'American weather is made at Medicine Hat.' In a sense this was true, for about sixty per cent of the storm areas--'lows' or region of low barometric pressure--come from the Canadian Northwest. The St. Lawrence Valley is the outlet for our storms. You know the saying about the St. Lawrence, don't you?" "No, tell us, Mr. Levin," begged Fred, always eager for some weather saying which he could put into the _Review_. "Up there," the Forecaster rejoined, "they say that when a stranger complains about the weather, a native will reply, 'Don't mind this, we'll have another sample along in about five minutes.' And, sure enough, they do. The St. Lawrence Valley is a magnet for weather changes and has, perhaps, more storms than any other valley in the world." "You spoke of the 'roads in the air,' sir," put in Ross, "how many are there?" "Five regular trails," the Forecaster answered. "The northernmost one begins at the Canadian Northwest, runs along the International Boundary, crosses the Lake region and disappears up the St. Lawrence Valley. The second starts at the same point in the Canadian Northwest, travels southeast to the lower Mississippi Valley--a little north of where we are now, boys--curves up to the Ohio Valley and also escapes by the St. Lawrence route. "A third storm track strikes into the Pacific Coast a little north of San Francisco and runs east and a little south until it joins the Ohio Valley and St. Lawrence track. A fourth develops in the southwestern states and runs along Texas and the gulf states to the Florida coast, where it curves northward along the Atlantic coast, though a few storms take a sharp turn in the Mississippi Valley and go Ohiowards. The fifth storm track is that of the West Indian hurricanes, which whirl around the West Indies and enter the United States south of Cape Hatteras or from the Gulf of Mexico and pass north or northeastward. A few of these hurricanes--like the famous Galveston type--sweep westwards a long way before the northward movement sets in. This type also goes to the St. Lawrence Valley.