before the northward movement sets in. This type also goes to the St.
Lawrence Valley.

"These five tracks are clearly marked, but as such areas are a thousand
miles across, it follows that the country for five hundred miles on
either side of the lines has its weather governed by them. Knowing these
tracks is of great importance in forecasting weather, because, while you
cannot always tell exactly what a storm is going to do, you definitely
know some of the things that it will never do."

"What sort of things, sir?" asked Fred.

"Well, my boy," the Forecaster answered, "if there's an area of low
pressure in Dakota, we know that it won't strike California; if there's
one in New York, we know that Maryland is safe. A storm will never go
down the Mississippi, nor up the St. Lawrence, but will always travel up
the Mississippi and down the St. Lawrence."

"There does seem to be something regular about it," the farmer remarked,
his interest growing, as the Forecaster took his pencil and sketched
out, across the map of the United States, the five great storm tracks.
"That's all right for storms, maybe. But how about a cold wave? Fred,
here, said that a cold wave was coming. Can you figure that out in the
same way?"

"Certainly," the weather expert answered. "As a matter of fact, it is
comparatively easy. A cold wave is simply a fall of temperature caused
by the cold air from the upper atmosphere sweeping downwards after a
cyclone of low pressure has passed."

"A cyclone?" ejaculated Ross, in surprise. "Is there always a cyclone
before a cold wave?"

"Always," the Forecaster answered, "but, unless I'm mistaken, Ross,
you're using the word 'cyclone' in the wrong sense. Most people do. I
suppose you think a cyclone is some kind of a whirlwind, a particularly
violent storm, eh?"

"Yes, sir," said Ross, "that's what I thought."

"Well, Anton can tell you better than that," the weather expert
rejoined. "Tell him what a cyclone is, Anton."

"So far as I can make out," the crippled lad answered, "a cyclone is a
whirl in the air, generally from five hundred to a thousand miles
across, in the middle of which the barometer is very low, and on the
edge of which the barometer rises. It always has winds that blow
spirally inwards, those in the United States whirling in a direction
opposite to the movement of the hands of a clock.

"So you see, Ross, to the east of a 'low' or ahead of it, the winds are
southeasterly, to the no