Reading the Weather

by Thomas Morris Longstreth

One of the most frequent starting places for investigators is the spots on the sun. They found that periods of three, eight, eleven, and thirty-five years should bear some resemblance; 1901 was eagerly looked forward to. They wanted it to correspond with the remarkably cool summer of 1867. When it started off in July with a temperature of 103 degrees, the highest ever recorded in Philadelphia, they concluded that the sunspots were fooling them. A connection between sunspots and weather has not been established, therefore, although they are now known to affect the electrical condition of the earth’s atmosphere. Longer periods of observation will permit comparisons that may yet define concurrent cycles of sunspots and weather.

A definite weather cycle has not yet been discovered, but one step in the way has been cleared up. We now are pretty sure of one cause for unusual single seasons of heat and cold.

There exist in winter great bodies of cold, dry air heaped up over Canada and Siberia, which are formed by the greater rapidity of radiation over land surfaces than over water. These mounds of cold air build up during December, January, and February and form great so-called permanent areas of high barometer. It is on the skirts of the Canadian high that the smaller highs form which sweep over our country, giving us our cold waves. Also in winter permanent lows form over the North Pacific and North Atlantic where warm currents afford continuous supplies of warm moist air. From the great Aleutian (Pacific) low spring most of the cyclones which swing down below the border of the Canadian high, make their turn somewhere in the Mississippi Valley, and then head for the Icelandic low.

It can be seen that if the Canadian high is a little stronger than usual and spreads a little farther south, then the northern half of our country will come more directly under its influence and we will experience an unusually severe winter. As the storms are pushed south and as the cold air pours into the northern quadrants the snow line is pushed south too. Hence all abnormally snowy winters are caused by a strengthening of the permanent Canadian high which may be central anywhere north of our Dakota or Montana borders.

Conversely, if this high is weaker than usual the cyclones can cross the country on a line farther north, there will be less snow, and the cold waves that follow will be less severe or even non-existent.

In summer the reverse occurs. Great oceanic highs are built up over the South Atlantic and South Pacific and a permanent low occupies the center of our continent. The character of the season is determined by the strength and position of these areas. The eastern states are affected especially by the slow movements of the South Atlantic low. The puzzle is why should these areas change their power and position, and if they must change why don’t they do it regularly? The puzzle will undoubtedly be solved. These great centers of action will be plotted against and observed from every vantage point by a thousand observers. A fascinating field for scientific speculation opens.

At present our Government exchanges daily observations with stations in Siberia, Canada, and the West Indies. The great storm-breeder, the Aleutian Low, is watched from Alaskan shores. In the Atlantic the Bureau needs stationary ships to record the growth and decline of the High over the Azores. Knowledge of the wind circulation from this would inform us whether our storms were to be shunted farther north and pushed somewhat inland. A storm which is pushed to the left of its normal track increases tremendously in intensity. Whereas a cyclone that limps slackly to the right of its normal line loses intensity at once. It misses coil. In this respect storms seem to resemble rattlesnakes.

The energy of the Azores High influences the number and destructiveness of the West Indian hurricanes: the larger the area is the closer do the hurricanes hug our shores and the more destruction do they accomplish.

The very sureness that the general average of the seasons is to be the same enables us to guess pretty accurately for individual purposes as to the kind of season coming next. A guess, let me add, is not a forecast. It is a gamble and disapproved of by the Bureau, but until they supply us with a basis for judgment we will have to go on guessing, for human curiosity is as near to perpetual motion as the weather is to the lacking fourth dimension.

One of these guesses is that if the winter has been a warm one the summer will be cool, for the very good reason that the yearly average does depart so slightly from the fixture. Unfortunately one hot summer does not mean that the following summer will be cool. Certain sequences of the seasons have been observed often enough to have been gathered into proverbs. Everybody agrees that “A late spring never deceives.” “A year of snow, Fruit will grow.” “A green winter makes a full churchyard.”