CHAPTER IX
HOW TO FORECAST FROM THE DAILY WEATHER MAP

IT IS NOT DIFFICULT TO BECOME WEATHERWISE AND THEREBY TO GAIN ADVANTAGES IN HEALTH, HAPPINESS, AND BUSINESS

The person who will take the time to learn to interpret the daily weather map has a decided advantage over those who are less progressive. The maps may be secured by applying to any Weather Bureau station. Many members of commercial associations, having the advantage of seeing the large glass weather map that is made each morning by an observer of the Weather Bureau and displayed on the floor of the association, have become expert weather forecasters. The value of the principal crops of the country is largely influenced by the weather, as are the prices of transportation and industrial stock; and there is hardly a business that directly or indirectly is not influenced by the prospects of coming weather.

Vessel masters, long accustomed to forecast the near approach of storms from the action of their “glass” (barometer), now have learned that the daily weather map shows them at a glance the height of not one but of many barometers scattered over a wide area and read at the same moment of time. They see that the direction and the force of the wind are the results of differences in air pressure; that the air flows from a region where the air pressure is great, that is to say, where the barometers are high, towards a region where the pressure is less, or where the barometers are low; and that the velocity of the wind will be in proportion to the difference in the pressure of the air. Coast-wise and lake shipping are therefore not only affected by the forecasts made by the Weather Bureau but by the forecast made by the masters themselves when they can get access to the daily weather map. Their own lives and the lives and property of others are in their keeping. But the great mass of intelligent people have no idea of the methods employed in the making of the weather map and of the many and widely diversified uses to which a study of its data would lead.

One first must learn of the simple manner in which the map is constructed; then, by a comparison of the map each day with the preceding chart, he soon will be able to detect the beginning of storms, trace them through their various migrations as they cross the continent and finally pass out to sea, bidding them bon voyage as they go in quest of a more eastern continent on which to bestow their blessings of rain and active, purified air; or, as it often may happen, shuddering for the fate of the mariner who is caught in their fierce vortical whirls, and for the land areas that may be laid waste by their gyrating force.

How the Weather Map Is Made. At 8 A.M. to-day Washington time, which, by the way, is about seven o’clock at Chicago, six at Denver, and five at San Francisco, the observers at some two hundred stations in the United States and contiguous territory were taking their observations and from carefully standardized instruments noting the conditions of the atmosphere. By 8:20 A.M. the barometers at each station have been reduced to sea level, that is to say, they have been made to read what they would if they were located at the level of the ocean. Thus differences in air pressure that are due to differences in elevation are eliminated, so that they may not obscure those due to storm conditions. Then, for purposes of brevity and accuracy, the observations are reduced to cipher form, and each filed at the local telegraph office. During the next thirty or forty minutes the observations, with the right of way over all lines, are speeding to their destinations, each station contributing its own report, and receiving in return such observations from other stations as it may require. The observations from all stations are received at such important centers as Washington, New York, Chicago, and other large cities having Weather Bureau stations, and from these centers daily weather maps are printed and issued at 11 A.M. each day.

Now turn to Chart 3. Heavy black lines (isobars, meaning equal pressure) are drawn through places having the same barometric reading. The readings are omitted from the printed Chart. By drawing lines for each difference of one tenth of an inch, the high and the low-pressure areas (called Highs and Lows) are soon inclosed in their proper circles. These lines run in oval or circular form, indicating that storms operate in the form of great atmospheric eddies; that there are central places of attraction towards which the air is drawn if the disturbance be a low-pressure area, with its usual accompaniments of warm, moist, and often rainy weather, and from which the air is driven if it be a high-pressure area, with cool, settled weather.

The word “High” is written inside the isobar marked 30.6, located in southern Oregon, and the same word is written inside the isobar marked 30.4, located on the South Atlantic coast, and also inside the isobar 30.04, which traverses Nova Scotia. These are the regions of great air pressure. The word “Low” is written at the center of the area inclosed by the isobar 29.6, which is situated in the State of Iowa. The latter is the region of least pressure. Sometimes there are several such regions shown on the weather map.

Why the Wind Blows. Under the pull of gravity the atmosphere presses downward and outward, thus causing it to flow from the several regions of great pressure towards regions of less pressure. Observe the arrows, which fly with the wind, and it will be seen how generally this law is obeyed. The velocity with which the wind moves from the High toward the Low depends on differences in air pressure, modified in the lower stratum by the friction offered in passing over surfaces of varying degrees of roughness, the speed being greater over a water surface with the same difference in air pressure than over a level unwooded prairie, and greater over the open prairie than over an irregular wooded area. To illustrate:

If the barometer were 30.5 at Bismark, Dakota, and 29.5 at Chicago, it would press upon the earth with a force of about seventy pounds greater per square foot at the first place than at the second. This difference in pressure would cause the air to flow from Bismark towards Chicago so rapidly that after allowing for the resistance due to friction on the earth there would remain a velocity of some fifty miles per hour, and Lake Michigan would experience a severe “Northwester”; and if the wind continued from the same direction for twenty-four hours a mighty sea would beat upon the eastern shore of the lake, and mariners and marine property would be at the mercy of a destructive tempest unless the Weather Bureau forecaster were alert and gave warning as soon as he saw such a juxtaposition of pressure distribution in the process of formation.

We will give careful attention to this chart, for when its details are understood, others will be easily read.

The chart shows a winter storm central in Iowa on December 15, 1893. The word “Low” marks the storm center. It is the one place in all the United States where the barometer reading is the lowest. The heavy black lines, oval and nearly concentric, about the Low, show the gradation of air pressure as it increases quite uniformly in all directions from the center of the storm outward.

The arrows fly with the wind, and, as will be seen, almost without exception are moving towards the Low, or storm center, clearly demonstrating the effect of gravity in causing the air to flow from the several regions marked “High”, where the air is abnormally heavy, toward the Low, where the air is lighter. As the velocity of water flowing down an inclined plane depends both upon the slope of the plane and the roughness of its surface, so the velocity of the wind, as it flows along the surface of the earth towards the storm center, depends on the amount of the depression of the barometer at the center and the resistance offered by surfaces of varying degrees of roughness.

Storms and Cold Waves Simply Great Eddies in the Atmosphere. Now picture in your mind that all the air inside the 30.2 isobar, as it flows inward, is rotating about the Low in a direction contrary to the movements of the hands of a watch, and you have a fair conception of an immense atmospheric eddy. Have you ever watched the placid waters of a deep-flowing brook and observed that where the waters encountered a projecting rock little eddies formed and went spinning down the stream? Well, our storms are somewhat similar eddies in the atmosphere, more or less perfect, that are carried along by the general easterly movement of the atmosphere in the middle latitudes of both hemispheres. But they are not deep eddies; the Low marks the center of an atmospheric circulation of vast horizontal extent as compared with its thickness or extension in a vertical direction. Thus a storm area extends from Washington, D. C., to Denver, Colorado, and yet extends upward only about six miles. The whole disk of whirling air, six miles thick and two thousand miles in diameter, is called a cyclone, or low-pressure area. It is important that a proper understanding be had of this fundamental idea, since the weather experienced from day to day depends almost wholly upon the movement of these migrating cyclones, or areas of low pressure, and the anti-cyclones, or areas of high pressure.

The temperature readings are omitted from each station, but the average temperature of each quadrant of the Low is shown by the large black figures. The greatest difference in temperature is seen to be between the southeast and the northwest sections. This is due in part to the fact that in the southeast quadrant the air is drawn northward from warmer latitudes, and in the northwest quadrant it is drawn southward from colder latitudes, and to the further fact that winds blowing into the west side of a Low have a downward component of motion, and those blowing in on the front, or east side, have an upward component.

One should gain a clear idea of the difference between the movements of the air in the cyclone and the movement of the cyclone itself, or its translation from place to place; how the wind must blow into the front of the storm in a direction partly or wholly contrary to the movement of the storm itself, and into the rear of the storm as it passes away; how the wind increases in velocity as it spirally gyrates about the center and approaches nearer and nearer the region where it must ascend; how the higher layers of air move spirally away from the center and thus cause an accumulation of air about and over the outer periphery of the Low, which in turn presses downward and impels the surface air inward. This whole complex system of motion moves eastward. Think of the sun drifting in space, while at the same time each of the planets maintains its respective orbit, and it will help one to visualize the phenomena of a migrating cyclone or anti-cyclone.

Chart 4, constructed from observations taken twelve hours later, shows that the Low has moved from central Iowa since 8 A.M., and is now, at 8 P.M., central over the southern point of Lake Michigan. The shaded portion of the chart shows that rain has fallen during the past twelve hours throughout nearly the entire region covered by the cyclone. This was due to the mixing of the air as the storm progressed, to the cooling by expansion as the air ascended, to the more rapid rotation about the storm center, because of the further lowering of the barometer at the center of the disturbance since the preceding chart was made, and especially to the more humid air encountered as the storm moved eastward and came nearer to the supply of moist winds,—the Atlantic Ocean.

On Chart 5 a line of arrows extends from the storm center westward to Wyoming, where the storm originated. A small cross inclosed by a circle marks its western extremity. Another cross located near Cheyenne shows where the storm center was located twelve hours after its origin. A third cross gives it location near Des Moines twenty-four hours after it started eastward. It was here that we began the study of this storm on Chart 3. A cross near Chicago indicates the distance traveled by the center during the third twelve hours, and Chart 5 shows its progress during the fourth twelve-hour period. When the storm was central at Cheyenne the danger warnings for mariners were displayed at all ports of the Great Lakes, as the forecaster knew that in accordance with general laws the storm must move toward the east. When it was centered at Chicago, danger warnings were displayed on the Atlantic coast from North Carolina to Maine, as it was known that long before the storm reached the ocean the in-rush of wind toward the storm center would cause a dangerous on-shore gale and the breaking of heavy seas on the shore line. All craft that could be reached with the danger signals made safe in port, except the great ocean liners, which are of such strength as to safely withstand almost any storm. A special set of observations ordered by the Washington office of the Weather Bureau from its stations in the region of the storm, and well in advance of it, kept the chief forecaster informed as to the progress of the cyclone, and before the storm center reached the coast the danger signals communicated to mariners the fact that the winds would soon shift to northwest as the center of the disturbance passed out to sea.

The reader’s attention will now be directed to the red lines on Chart 5; they pass through places having the same temperature, but for simplicity the readings of temperature, whereby these lines were located, are omitted from the printed chart. Observe the line marked 40°; it passes across southern New England to western New York, but when it reaches the center of the storm it encounters the cold northwest winds blowing into the storm on its west side and is forced southward to Texas.

Charts 3, 4, and 5 give a graphic history of one severe winter storm. In summer such general storms do not often occur. They are frequent in spring and fall, but of higher temperature and less severity than in winter. In summer Lows drift sluggishly across the continent; the barometer at the center of the cyclone is usually not more than two to four tenths of an inch below the pressure of the Highs, and the rain, instead of falling in a broad sheet, as shown by the shading of charts 4 and 5, falls in numerous sporadic outbursts, each of which is but a few square miles in area, their combined surfaces usually covering only a part of the region over which passes the Low.

Cold Waves and the Speed of Storm Movement. Highs and Lows drift across the continent from the west towards the east at the average rate of about six hundred miles per day, or about thirty-seven miles per hour in winter and twenty-two miles in summer, the first at about the rate of an express train, and the second approximating the speed of a freight. The Highs are attended by dry, cool, and settled weather. By a vortical action at their centers they draw down the cold air from great altitudes above the clouds. In winter, when vortical action is vigorous, they may reach upward to an altitude of seven miles. Air starting downward from this region has a temperature of some 70° below zero. We know this from the records secured by sending aloft free balloons carrying automatic thermometers. (Chapters II and III.) This air heats by compression because in its downward movement it is continually leaving more and more air above it to exercise pressure upon it. It gains about twenty degrees with each mile of descent, and if there were no other factors to the problem it would be hot air when it reached the surface of the earth instead of cold air. But early in its descent it gains such heat as to melt and evaporate the ice spiculæ floating at the height of the fleecy cirrus clouds; then it evaporates and clears away the moist clouds lower down and finally creates such diathermancy (the capacity to transmit heat without absorption; see Chapter V) that the heat lost by radiation to a clear sky causes what we call a “cold wave”, and this notwithstanding the heat of compression.

The forecaster first observes a cold wave in the northern Rocky Mountain region, in the form of an intense High. It will travel southeastward to the center of the continent, and often to the Gulf if it is preceded by an active Low that is located on a low latitude, as the latter will draw southward the frosty air of the High; after that the course of the storm will be more nearly eastward. Now it is of rare occurrence that a cold wave gains entrance to any considerable area of our territory without warning, but in the early days of the Weather Bureau they too often reach Iowa, or States farther east, without any notice whatever. It was then discovered that a certain type of weather map preceded such failures of the forecaster. One who is interested in gaining early knowledge of the approach of a cold wave to the United States should watch not only for the appearance of abnormally high barometer readings, from the stations of the Canadian Northwest, or from Montana and North Dakota, but especially for a crescent-shaped Low, with one horn of the crescent touching Lake Superior and the other extending into the middle Rocky Mountain region, at about Colorado. This Low will appear to be an innocent affair; there may be a small secondary Low in each end of the crescent, and no High of any importance in the northwest, for which one ordinarily would look in anticipating a cold wave. But when this crescent-shaped Low appears on the morning weather map, a High of marked intensity invariably will develop with great suddenness over Montana and North Dakota and bring a cold wave to the Middle Mississippi Valley before the next morning, if the time of year be winter.

Do not forget that the Low is as important as the High in causing a cold wave, for the High that brings the cold air must follow in the track of the Low and will be attracted by the latter in proportion to its lowness, as indicated by the isobar inclosing the center of the Low. A cold wave will reach the Gulf only if the preceding Low originate in Texas; it will be confined to the Ohio Valley as the limit of its southern influence if the preceding Low originate in Colorado; and it will only skirt the northern border of the United States and the Lake region if the Low begin in Montana.

More and more is man applying science to commerce and industry. When the weather map, which was unknown but little more than half a century ago, indicates the formation of a heavy body of cold air in the extreme northwest, the chief official forecaster at Washington is on the alert; he orders special observations every few hours from the Weather Bureau stations directly within and well in advance of the cold area, and as soon as he becomes satisfied that a cold wave is on its way, the previously arranged system of disseminating warnings is brought into action, and by telegraph, telephone, flags, whistles, bulletins, and other agencies, the people in every city, town and hamlet, and many in the stock and farming regions, are notified of the advancing cold twelve to twenty-four hours before it reaches them.

Charts 6 and 7 show how the Weather Bureau defines a cold wave. There must be a fall of sixteen degrees, eighteen degrees, or twenty degrees within thirty-six hours and a certain degree of coldness must be reached. The charts show that what is a cold wave in the Gulf region is far from one in the northwest.

Chart 8 shows the lowest temperatures experienced in the United States since the founding of the Weather Bureau, 1871 to 1913. Note the influence of the Pacific Ocean in forcing the zero line from Arizona northward to British Columbia.

Chart 9 shows the number of times that a cold wave occurred at each station of the Weather Bureau for a period of ten years. The number is greater for northern New England than for the Red River of the North Valley, because practically all the cold waves that cross Minnesota reach New England; and the latter also receives fierce boreal visitors that come to it from the Hudson Bay region lying directly northeast, which do not visit any portion of Minnesota or the region farther west. During the period not a single technical cold wave occurred at the coast stations of California, Oregon, or Washington, while Red Bluff and Sacramento were the only two places in California west of the Sierras, and Roseburg, Oregon, the only station west of the Cascade Range that had any, the numbers being one, two, and five respectively. In the Florida peninsula south of Jacksonville, Tampa had two, while none occurred at Miami. Sometimes the temperature falls lower than that required for a cold wave, but not within the period of twenty-four hours required by the regulations. A notable case in point is the severe cold wave in California in January, 1913, the lowest temperature ever observed being recorded at San Diego on the 7th, when the minimum fell to 25°.

Cold Waves Tempered by Great Lakes. The severity of cold waves is markedly modified by the Great Lakes, especially in the fall and the first part of winter, before much of the water surface is covered with ice and snow. Not only is the number of cold waves much less at stations of the Lakes than at near-by places in the interior, but there is a marked variation in the number that occur at the Lake stations, depending upon which side of the lake and how close to the water the station is located. The most striking differences are noted in the Lake Michigan region, the number on the west shore being five or six times as great as on the east side. Milwaukee shows a count of forty-seven as compared with nine at Grand Haven. This lake influence affects the entire Lower Michigan peninsula, but it is not so great in the interior and eastern sections as along the west shore, Grand Haven’s nine standing out against fourteen, fifteen, and twenty-three for Grand Rapids, Detroit, and Port Huron. A similar condition is noted in New York State; Buffalo, Rochester, and Oswego, near the lake shore, had twenty, twenty-seven, and twenty-nine cold waves respectively, while the interior stations of Ithaca, Binghamton, and Syracuse had thirty-eight, forty-five, and fifty-two.

Cold Waves Tempered by the Heat of Cities. Another reason for the lack of uniformity in the recorded number of cold waves in the various sections of the country is the difference between city and suburban temperatures. Stations located in small villages or in the open land will show a greater number of recorded cold waves than those located in large cities, where the heat stored up by pavements and brick buildings during sunshine each day, and where the heat from thousands of chimneys, and maybe millions of human beings, holds the minimum temperature of night much above that of the free air in the open country. Charles City, where the instruments have open country exposure had sixty-five cold waves, which far exceeds the number recorded at any other station in Iowa.

No matter how severe may be the cold wave that appears in the northwest, it will not extend over Wyoming, Colorado, Utah, and any region south of them, unless the center of the High extends well over the Rocky Mountain Divide. Otherwise it will come down the east slope of the mountains and the cold will not cross them.

In the Lows the conditions of the air and its movements are exactly the reverse of what they are in the Highs; the air is warmer and moister, it is drawn spirally inward from all directions instead of being forced outward as in the High, and it ascends as it approaches the center of depression, sometimes causing rain or snow as it cools by expansion during its ascent. While the air cools with ascent in the Low at the same rate that it warms with descent in the High, the earth experiences a general warming effect with the passage of the Lows, because the air falls but little in temperature as it rises before it reaches its dew point, and then there is a liberation of the latent heat of condensation (see Chapter V); and what is more important, there is formed a covering of clouds that checks or wholly stops radiation outward from the lower air. However there are times when the passage of Lows produces a cooling effect. This is when abnormally hot weather has prevailed for some days; then the air may be mixed, washed, and cooled by thunder-showers.

Highs and Lows alternately drift across the continent in periods of about three days each. They are a part of the divine economy that provides for the seedtime and the harvest, for, as previously stated, the Lows draw the warm, vapor-bearing currents inland from the Gulf and the ocean and cause them to deposit their moisture far to the north and west. Four sevenths of all our storms come from the middle or the north plateau regions of the Rocky Mountains, or at least enter our field of observation from those regions, and pass from this arid or sub-arid section of the continent easterly over the Lakes and New England, producing but little rainfall. The greater part of the remaining three sevenths are first observed in the arid regions of our southwestern States; they always move northeastward and can be depended on to give bountiful rainfall so soon as or a little before they reach the Mississippi River. Some of them cross the Atlantic and affect the continent of Europe. Charts 10 and 11 show the courses of storms in this country, and where they originate, or are first brought under the survey of our system of observation.

West Indian Hurricanes. A few of the most severe storms that touch any portion of our continent originate in the West Indies and travel in a northwesterly direction until they touch our Gulf or South Atlantic coast, when, passing from the influence of the northeast trade winds which carried them westward, they recurve and pass along our eastern coast, usually with their centers offshore and following the Gulf Stream. These violent atmospheric convulsions are usually detected in the process of formation through the effectiveness of the storm-warning service established by the writer during the Spanish-American War, under the direction of the President, for the purpose of giving warning to our fleet before the coming of a hurricane. The President realized the great part played by storms in many of the naval battles of the past, and it may be surmised that he was more afraid of a West Indian hurricane than he was of the Spanish Navy. But Cervera was beaten and the blockade was raised before the hurricanes of 1898 began.

Galveston Hurricane. The new Weather Service, with a cordon of stations down the Windward Islands and along the north coast of South America, surrounding our fleet, and inaugurated as a war measure, so demonstrated its value in locating and giving warning of the coming of a hurricane soon after the end of the war that Congress continued it as a permanent instrument of peace; and when the destructive Galveston Hurricane occurred in 1900 it detected the storm at its inception and so fully advised shipping of the storm’s movements that not a vessel was lost as the storm roared and gyrated across the Gulf of Mexico and crashed upon the Texas coast, destroying a large part of the city and drowning six thousand people.

The hurricane is simply a rapidly gyrating cyclone; it usually is only one to three hundred miles in diameter. The storm that destroyed Galveston moved across the Caribbean Sea at the rate of only about eight to ten miles an hour. It increased its rate as it moved northward, crossing the Gulf at about fifteen miles per hour. The speed of translation was so slow and the velocity of gyration so rapid that immense swells were propagated outward from the center of the storm; they reached the Texas coast some sixteen hours before the storm itself reached Galveston. As it moved northward to Iowa its velocity of translation increased and its rate of gyration decreased, so that it crossed the Lakes with both movements at about sixty miles per hour. At Galveston the anemometer blew to pieces after recording one hundred and thirty miles per hour.

Danger to Atlantic Coast Summer Resorts. The writer frequently has been asked as to the possibilities of a populous Atlantic coast resort being submerged by the waters driven inshore by a hurricane, or being lifted up in the center of the storm as the result of decreased air pressure inside the cyclonic whirl. The answer is that such a catastrophe is possible to any Atlantic coast city (more especially those south of Norfolk) that is not protected by a heavy breakwater of ten to twenty feet above sea level, and whose building foundations and walls are not of brick or concrete for at least ten feet above the water level. It would be necessary for a West Indian hurricane of unusual intensity—one similar to that which wrecked Galveston—to be considerably deflected westward out of its normal track in order to hit one of our coast cities north of Chesapeake Bay so that the center of the storm would pass over it, or near enough to cause destruction. In Galveston there was little damage to strongly constructed buildings of brick or stone.

The Breaking of Droughts. It is most important for the forecaster to know when and how droughts may be broken. He will observe that when the great cereal plains are famishing for moisture the Lows all originate on the middle or north Rocky Mountain plateau, in the region of Colorado or Montana, and that the drought continues until the Lows begin to form in the extreme southwest—in Arizona, New Mexico, or Texas. As previously stated such Lows always bring rain as they move northeastward.

Warm Waves. There come in summer periods of almost stagnation in the drift of the Highs and the Lows across the continent. At such times if a High be centered in the South Atlantic Ocean, with its center at Bermuda, and its western limits extending into the South Atlantic coast States, there will result what is popularly known as a warm wave, for the air will slowly and steadily move from the southeast, where the pressure is greater, towards the northwest, where it is less; it will receive constant accretions of heat from the radiating surface of the earth, and finally attain to a temperature that is extremely uncomfortable to all forms of life, that lowers the physical stamina, and that largely increases the death rate. This superheated condition of the lower stratum of air in which we live continues until a Low develops in the southwest and a High in the northwest, which relation, as we already know, soon brings rainfall to the interior of the country.

V-shaped Lows are reasonably sure to cause precipitation, and if the barometer at the center of the Low be five to seven tenths below the outer limits of the depression, heavy precipitation and destructive local storms may be expected.

Thunderstorms. The thunderstorm is caused by cold and heavy air from above breaking through into a lighter and superheated stratum next the earth. Some of them have a horizontal rolling motion which throws forward the cool air in the direction in which the storm is moving. It seldom is more than five or ten miles in width and twenty to thirty miles in length. In general, thunderstorms move from the west toward some eastern point, more often southwest to northeast.

The frequency of thunderstorms is the greatest with ill-defined Lows whose pressure is but little below the normal air pressure of thirty inches. Any depression of the barometer slightly below the level at surrounding stations—such as occurs when a weak High of only thirty inches, or thirty and one tenth inches, breaks up into two or more areas, with slightly lower pressure between them—is fruitful of thunderstorms. A High of but modest intensity advancing eastward into a region of slightly lower pressure and much higher temperature causes thunderstorms along its eastern front. A temperature of 80° on the morning weather map, with a high humidity, seldom can endure beyond the second day without a break and the coming of cooling thunder-showers. Any Low with abnormal heat and humidity in its southeast quadrant is usually attended with numerous thunder squalls in the regions of high temperature and moisture.

Of the thunderstorm days in the United States few occur in the Rocky Mountain regions or in northern New England. The greatest number is in Florida and the Gulf States and thence northward up the Mississippi Valley.

The Moon Has No Influence on the Weather. The moon used to be the farmer’s most valued friend as a forecaster of the weather and as a guide in the planting of crops, but a higher order of intelligence is causing this fallacy to pass away. The moon’s nearness to the earth and the fact that its phases occur in about seven days, which is about twice the period of storm recurrence, in the minds of many have endowed it with potency in the influencing of our weather. Rain may occur on the same day of the week for several weeks in succession, but only occasionally, while the moon is constantly progressing from one phase to another. The few cases that prove the mistaken theory are taken as proof conclusive, while the many cases that do not prove acceptable to the moon forecaster are ignored and not mentioned to his friends nor even acknowledged to himself. One is reluctant to have a belief disproved, no matter how ridiculous it may be. In fact, the more untenable it is, the more tenaciously some adhere to it, as though they were loyally standing by an old friend who had made mistakes, but who still was good at heart. The attraction of the moon, because of its nearness and notwithstanding its small mass, is far more potent in the raising of the tides of the ocean than is the sun, but its attraction on our atmosphere produces a tide of only four thousandths of an inch of the barometer, an influence that is shadowy and without the least influence in causing storms, or changes of any kind in the weather; and there is no possible way in which the moon could influence the germination of seed or the growing of crops.

Equinoctial Storm. As the summer wanes the Lows become more pronounced and the sporadic showers give place to general rain storms along in September. There is no objection to these storms being known as “Equinoctial”, except that any date in the latter half of September is as liable to show a beginning of these storms as is the 21st or the 22d. The equinox simply marks the middle period in the transition from one type of weather to another.

Forecasting from Halos. The halos that sometimes surround the sun or the moon indicate the coming of precipitation to the extent of making manifest the presence in the upper air of large quantities of vapor of water in a congealed state. When the vapor of water cools quietly in the laboratory it frequently forms minute spheres of water, which, strange to relate, may remain liquid all the way down to zero and below; but if touched or jostled they instantly turn to ice, in the form of spiculæ, or needles; they are simply hexagonal slender prisms capped by hexagonal pyramids. These needles rotate or spin about as they fall. The geometrical relations of the facets of the crystals to the axis of rotation and to the line along which they fall are a complex problem in optics. Suffice to say that the observer, looking through a filmy cloud of such crystals, would see in one part of the sky a halo, in another part an arc of light, and in other directions bright spots like the sun, all of them arranged symmetrically with regard to the sun and the observer’s zenith. A lunar halo is a large ring concentric about the moon. A secondary halo surrounds the first. Mock suns or mock moons may appear coincident with solar or lunar halos. The ice prisms through which one sees the phenomena both refract and diffract the light as it passes through the cloud and by partly decomposing the rays render visible a part of their elementary colors. The red is on the inside, next to which is a little yellow or green, with bluish white on the outside. In coronas, which are much smaller, the red is on the outside. A detailed description of these phenomena may be found in Moore’s “Descriptive Meteorology” (Appleton).

Tornadoes. The cyclone has a diameter of a thousand to two thousand miles, the hurricane about one to three hundred and the tornado only one to ten hundred feet. The hurricane is much more destructive than the cyclone, and the tornado is incomparably greater in velocity of gyration and rending force than the hurricane. New England, Florida, and the wide region including the eastern slope of the Rocky Mountains westward to the Pacific are nearly free from the atmospheric convulsions that cause the tornadoes, and they are infrequent in any Atlantic coast State, but numerous in the States bordering on the Mississippi River, and in the eastern halves of Oklahoma, Kansas, and Nebraska. During a year of great frequency of tornadoes, about ninety storms occurred, while during some other years the number has been as low as twenty. The direction generally is toward the northeast. The average rate of movement of the tornado cloud is about twenty-five miles per hour and the width of its destructive path only five hundred to one thousand feet; the time of passage is less than half a minute. It does not come upon one unseen and unheralded. Many times the advancing funnel-shaped clouds may be seen, and they always are accompanied by a great roar which may be heard for miles. Except a tornado cellar, the cellar of a frame house is the safest place. The writer has examined either the wrecks or the records of hundreds of tornadoes and does not know of a single case of a person being killed by a tornado in the cellar of a frame house. If one is in the open and a tornado approaches, never flee to the north or to the east, but rather to the northwest, and one needs to travel but a short distance to pass out of the track of the monster. The tornado always twists counter clockwise, the same as the cyclone in whose southeast quadrant it nearly always occurs. On the southeast side of the path there are indrafts; so that it is safer, unless the track of the oncoming storm is clearly seen to be well to the north of the observer, for one to run toward the northwest. Persons have stood near to the north side of a tornado track during its passage without suffering injury. If a cave, the cellar of a frame house, or a narrow ditch cannot be reached, the best thing to do is to lie flat on the ground as far from buildings and trees as possible.

The tornado is essentially an American storm, doubtless caused by the running together, in the southeast quadrant of a cyclone, of cold northwest currents and warm winds from the southeast, at a time when the latter are saturated with moisture. They are confined almost entirely to the region between the two great mountain systems of the continent, none occurring in the Rocky Mountains and but few east of the Alleghanies. The north and south trend of our mountain systems, quite different from the systems of Europe and Asia, facilitates the coming together of conflicting winds of widely different temperatures in the lower reaches of the atmosphere where there is an abundance of water vapor; no tornadic whirls probably can occur without an abundance of water vapor and the energizing effect of the heat liberated in the whirling cloud as this vapor is suddenly carried aloft and liberated by condensation right in the center of the disturbance. Because of the relation of the trend of its great mountain systems to its oceans, the United States occupies a somewhat unique position meteorologically in the world. Its atmospheric conditions are more active than those of any other continent, which conditions are beneficial to the people of this country.

When to Watch the Weather Map for Tornadoes. The four conditions essential to the formation of tornadoes are as follows: