To Libby Lyman, age 15, of Stanley, N.C., for her question:
Why does our weather come from the west?
Hurricanes howl up the Atlantic coast from the southeast, and icy blizzards sweep down from the polar regions. But these are local weather events. Over most of North America, the major weather events are brewed in the west and then whirl their way slowly eastward to the Atlantic.
A weather map shows the great air masses of high and low pressure. The lines of atmospheric pressure, one inside another, are called isobars, and the picture of an air mass looks somewhat like the ripples on a pool. Day by day, you can trace its path for perhaps a week and its path is almost always from the west to the east.
In Florida and Mexico, the big weather events usually move in the opposite direction. Here, the storms that hatch in the Atlantic whirl westward to the Pacific. North of the Arctic Circ1e, the Weather events also tend to move eastward. And the Satrie pattern of Weather belts is repeated south of the equator.
These Weather belts are the belts of the prevailing winds. The trade Winds blow between the equator and Latitude 30 degrees North, which cuts through Jacksonville, Fla. They are northeasterly winds, and the weather events that hatch in this wind belt are usually carried eastward by trade winds.
The prevailing westerlies blow between 30 degrees arid 60 degrees North. Most of North America is swept by the westerly winds, which circle around and around the globe. The big weather events that form in this wind belt are usually wafted along from the west to the east.
Pockets of light air or dense air tend to form here acid there over land arid sea. A pocket of light air forms a low pressure cell, and air flows in from all sides to even the atmospheric balance. A pocket of dense air forms a high pressure Cell with winds flowing out froth the Center. The spinning earth gives a twist to these winds, and both high .:and low pressure cells swirl around in spirals.
A mass of high pressure tends to bring us a spell of balmy weather. As it passes overhead, the breezes at first come from the northwest. Later we get the winds on the other side of the spiral which come from the southeast. Though the winds change, the entire air mass is being wafted eastward across the land by the prevailing westerlies that circle the globe.
Sometimes a major weather event is strong enough to sweep from one wind belt to another. The polar easterlies often rip down into Westerlies and upset our normal weather picture. The hurricanes that hatch in the West Indies are wafted east by the trade winds, but the land mass of North America, often forces them to turn north. For a time, they battle the westerlies, but at last the prevailing winds blow them back out to sea.