CHAPTER XIV

WEATHER MAPS AND FORECASTS

“Forecast”--with the stress on the first syllable when it is a noun, but often on the second when it is a verb--is a word that meteorology has made peculiarly its own. This fact is not the result of accident, but of design.

The founder of scientific weather prediction in Great Britain was Admiral Robert FitzRoy--the same talented officer who explored the coasts of South America in the _Beagle_ and had Darwin for a fellow-voyager--and his first predictions were issued in 1861 from the Meteorological Department of the Board of Trade, which was under his charge. The boldness of this pioneer undertaking is not easily realized by the present generation, which is accustomed to see the official weather forecast at the head of every daily newspaper. Weather prognostication had previously been the undisputed province of charlatans and quacks. For a civilized government to embark upon such an enterprise must have seemed, to the educated public, very much like charging the Astronomer Royal with the duty of casting horoscopes.

There is much virtue in a name. A few years ago the United States Bureau of Fisheries persuaded the American public to eat dogfish by changing its name to “grayfish.” Similarly, FitzRoy induced the British public to take his weather predictions seriously by calling them “forecasts.” The name has stuck; and nowadays, throughout the English-speaking world, the expression “weather forecast”--except as applied comprehensively to predictions of the “long-range” variety--means something decidedly less chimerical than the average weather prophecy.

It is still necessary, however, to emphasize the distinction. There are probably many people among us, well above the illiterate level, who have no clear idea as to what constitutes a scientific weather forecast. The distinguishing feature of such a prediction, apart from the fact that it is made by a trained meteorologist, is that it is, in all cases, based upon a weather map.

The forecasting machine is a big one, with its human gear spread over a wide territory. Eventually it will be spread over the entire globe, and then we shall have better forecasts. A little manual entitled “The Weather Map,” published by the British Meteorological Office, says:

“The making of a single forecast in any one of the meteorological offices of Europe, America, Australia, or the Far East requires the organized cooperation of some hundreds of persons; about a hundred observers who note the necessary observations simultaneously at as many separate places and hand in their reports to the telegraphists who transmit them to one center, where the meteorological expert charts them on a map and draws therefrom the conclusions on which the forecasts are based. The preparation of the map is an essential part of the process. No meteorologist in the modern sense attempts to forecast the weather without reference to a map prepared either by himself or by some one with whom he is in direct communication, from observations transmitted by telegraph for the purpose. No amount of weather wisdom or weather lore or experience is a substitute for the map. The more expert and accomplished the meteorologist, the more certain he is that all he can do without the materials for constructing a map, though he may have a barometer and other instruments at hand, is to make a guess at what the map is like and think out from that what the weather changes are likely to be. It is a common experience of professional meteorologists away from their base to find themselves appealed to for an opinion about the weather, judging from the signs of the sky alone, because they are learned in such things. That is exactly what they are not. Accustomed to refer everything to a map, without one they feel themselves to be rather worse off than those who are unaccustomed to its use. A modern meteorologist thinks in maps; his language and modes of expression are formed thereby.”

While the weather map is prepared, first of all, for the use of the forecaster, who makes his predictions from the map before it has passed beyond the manuscript stage, it has other important uses, which justify its publication and widespread distribution. The weather map is a weather newspaper. Like other newspapers, it is founded on a system of telegraphic dispatches and is designed to keep us in touch with what is going on in the world. Weather news is of general interest because weather plays a part in most of the doings of humanity. Sometimes the news we read on the face of the map merely satisfies our curiosity; at other times it renders us more substantial service.

By way of illustrating the manifold purposes served by weather maps, let us set down two cases that are, perhaps, at opposite ends of the scale of utility. Our first case is that of the traveler who scans the map to see whether the atmospheric conditions at his distant home are propitious, that day, for some outdoor pleasure event on the family program. This we may describe as a sentimental use of the map. The second case is that of an aviator embarking on a flight some time in the fore part of the day, soon after the morning map has made its appearance. Here is a case in which the map is of vital utility, purely as a record of current conditions. The aviator is not concerned with the forecast of the morrow’s weather, unless he is making an unusually long flight, but he is immensely concerned with the winds and weather prevailing along his route at the time he flies, and these will not, as a rule, differ radically from the conditions shown on the map of the same morning.

Since weather affects business in a variety of ways, people who have business interests away from their places of residence frequently have occasion to consult the weather map. The influence of the weather on crops explains why the map is watched with keen interest by dealers in agricultural products. Owners of vessels navigating the ocean or the Great Lakes take a practical interest in the present as well as the future location of storms. And so on. It is not necessary to prolong this list of those who use the weather map, because the popular demand for it speaks for itself. It is worth while to record the fact that the demand far exceeds the supply. In this country the Weather Bureau has been constantly harassed with urgent requests for the publication of maps at places where, in consequence of limited appropriations, it has not been possible to issue them.

The weather maps published in various parts of the world exhibit much diversity in detail, though they have, of course, many features in common. As a rule a weather map covers a wider area than that of the country in which it is published. The aim has always been to make these publications international, as far as practicable. The longest continuous file of printed daily weather maps in existence, viz., that established in France by Le Verrier in 1863 and still published, has been called from its beginning the “Bulletin International.” It embraces nearly the whole of Europe, a little of Africa, Iceland, and the Azores. The other European maps now cover the same area or a considerable part of it. Before the war the Russian meteorological service was issuing a map that included, in addition to Europe, a wide zone of Asia extending all the way to the Pacific Ocean. The United States map, as published in its most extensive form at Washington, comprises the whole of this country and southern Canada, besides presenting tabulated statistics for more distant parts of the world. Manuscript maps prepared daily at Washington have a still broader outlook; they are drawn on a base map that covers the northern hemisphere, and the printing of a map of this sort, including a chain of stations extending around the globe, was undertaken in 1914, but was interrupted by the war. The map published by the Argentine Meteorological Office, at Buenos Aires, covers more than half of South America. Most national meteorological services issue weather maps, but there are a few that do not. No such maps are published in South Africa or any of the South American countries except Argentina.

Thus there is still much room for the horizontal extension of the weather map, and there is even more room for its vertical extension. Daily weather maps for aeronauts (chiefly wind maps) are now more or less on the programme of all the leading meteorological services, and in a few cases their publication has already begun. Probably the first maps of this character, showing the winds at various levels over a whole country, were those that began to appear in Italy in 1913. The British Meteorological Office now publishes such maps, showing winds and clouds at different levels over the British Isles at three hours of the day. In the United States maps of the “wind aloft” are prepared daily, at Washington, from the reports of kite and balloon stations, but they are not yet published. The Weather Bureau has, moreover, invented an ingenious method of depicting the winds at several levels on a single map; in other words, constructing a map in three dimensions. This consists of attaching arrows to little metal posts erected on an ordinary weather map at points corresponding to the location of the upper-air stations. Each post bears a series of arrows--one arrow for each level charted--and the arrows are set in positions showing the direction of the wind at each level. Numbers on the arrowheads indicate the force of the wind. When the map is finished it is photographed from two different angles so as to make a pair of pictures suitable for viewing through a stereoscope. These stereoscopic pictures were formerly made every day and a file of them is available for reference and study.

There are a few conspicuous points of difference between the weather maps issued in foreign countries and those issued in this country. Thus a majority of the foreign weather services publish two or more charts on the same sheet; either for the sake of showing different meteorological elements separately or, in most cases, to represent the conditions prevailing not only at the hour of the current morning observation, but also at certain hours of the previous day. One of the three editions of the British map includes four charts, corresponding to observations at four different hours. By means of such series of charts one can observe the recent changes of weather as well as the current conditions. Weather maps published in the United States show primarily the conditions at 8 a. m., Eastern Standard Time, of the morning of issue; though certain features of past weather are also indicated, including changes of temperatures, movements of storm centers, etc. Evening maps are drawn at Washington and at many other places, but are not published.

In this country the publication of weather maps has been carried out on a much more liberal scale than elsewhere. Instead of issuing maps at only one or a few places, as is the custom in other parts of the world, it has been the policy of the American service to publish them at populous centers all over the country. In some cases they are printed or manifolded at the local Weather Bureau station, and distributed by mail and messenger; in other cases they are published in the newspapers. The daily circulation of the maps has thus, at times, run up into the millions. This comprehensive duplication of the chart is made possible by special arrangements with the telegraph companies. The reports of observations are, to a large extent, sent over circuits, along which the telegraph offices, besides forwarding the local report, copy the reports from other stations as they pass over the wires. Certain stations, forming connecting links between the circuits, effect the transfer of collected reports from one circuit to another; so that, in a very short time, upward of 150 stations receive the reports from a large number of other stations. The maps issued at stations or published in newspapers are generally rather crude, though they answer their purpose; but the large lithographed map issued every day at the Central Office, in Washington, is much the most artistic production of its kind published anywhere in the world.

Large weather maps, drawn with colored chalk on a ground-glass base, may be seen at certain produce exchanges and railway stations, on the “boardwalk” at Atlantic City, and in the Capitol at Washington. Motion-picture weather maps, made from series of maps showing conditions at successive intervals of time, have been prepared experimentally in this country and abroad.

The reports used in the construction of weather maps are telegraphed from the stations in cipher, in order to save expense. In Europe groups of figures are used for this purpose, but the United States Weather Bureau makes use of a word code, which offers the advantage over a figure code that, as a rule, mistakes in the telegrams can easily be detected by anybody familiar with the code. The American weather code is something of a literary curiosity. In each of the many thousand words it contains there are certain significant letters, and these must fall in certain sequences in order to convey the information required. The English language has been ransacked--and somewhat stretched--to secure the necessary words. Observers consult the code book in enciphering their reports, but translating is easily done without the book by those who have mastered the relatively simple principles on which the code is constructed.

The language of lines, shadings and symbols used in weather maps can be learned in a few minutes, and it is, as a rule, fully explained on the face of the map. This is true of foreign maps as well as American. A full-fledged weather map is hardly susceptible of reproduction in a book of ordinary dimensions. The simplified map that we show here, taken from a Weather Bureau bulletin, will, however, serve to illustrate some of the features of such publications. The reader should first fix in his mind the explanations printed at the lower left-hand corner of the map and then study the map in the light of what has been said in Chapter VIII about the circulation and movements of highs and lows. On this map we have an exceptionally well-developed high over the middle of the country and a pronounced low on the Atlantic coast. The former, with clear skies and very cold weather, constitutes a cold wave. The latter is attended by a widespread snow storm and, as may be inferred from the crowded isobars, by stormy winds.

Now bear in mind the fact that charts identical with this one, except that they contained much more detailed information, were issued in all the more important cities and towns of the United States on the morning of January 25, 1905, about a couple hours after the taking of the morning observations, at 8 a. m., Eastern time. The same morning, weather forecasts, cold-wave warnings and storm warnings, deduced from this map, were issued to some hundreds of thousands of addresses by telegraph, telephone, mail, and messenger. The map itself conveys information comparable in interest to the news of public events published on the first page of the newspapers the same day. The forecasts and especially the warnings are, in such a case, worth millions of dollars to the people of the United States. The following account of the cold wave appears in the Annual Report of the Chief of the Weather Bureau for 1905:

“A severe cold wave appeared over the Dakotas, Minnesota, Nebraska, and Iowa on January 24, 1905, and on the 25th covered the central and upper Mississippi valleys and extended over the northern portions of the east Gulf States, the line of zero temperature reaching into northern Tennessee. On the 26th the cold wave covered Florida, and temperatures below freezing were reported as far south as Tampa and Jupiter. At the latter place, the minimum temperature, 24 degrees, equaled the lowest ever recorded since the establishment of the Weather Bureau station at that point. Considerable damage was done to orange trees where groves could not be fired or protected. Ample warnings had been given of the expected low temperatures.”

The subject of making forecasts from a weather map is one concerning which some big books have been written, and it cannot be dealt with very satisfactorily in the brief space at our disposal. There are two cardinal rules--viz., (1) the weather has a characteristic distribution in relation to the distribution of barometric pressure, and (2) pressure systems, with their attendant winds and weather, move, in a general way, from west to east--but these rules require various qualifications and are subject to various exceptions. Thus highs and lows generally take rather circuitous routes in getting, eventually, to the eastward, and sometimes they break up or fade out. The high shown on the annexed map actually moved much more south than east during the following twenty-four hours, while the low moved up the coast; i. e., more north than east. These were, however, the movements expected by the experienced forecaster.

Well-developed highs are nearly always regions of clear weather and, in winter, of cold weather. Lows are attended by clouds and precipitation; rising temperature usually precedes them and falling temperature follows them. The professional forecaster recognizes several types of pressure distribution other than ordinary highs and lows, and they, also, have their characteristic winds and weather. The seven typical forms of isobars, as classified many years ago by R. Abercromby, are: Cyclone; anticyclone; secondary; V-shaped depression, or trough; wedge of high pressure; col, or saddle, between two anticyclones; and straight isobars. These may be combined in a variety of ways on the weather map. The forecaster learns to classify these combinations consciously or subconsciously, and grows familiar with their habits and mannerisms. Forecasters spend a good deal of time in studying the files of weather maps for past years; but the results of such studies are not easy to reduce to definite statements. Scientific forecasting is, in its present stage, almost wholly empirical. The dependence of weather changes upon the phenomena of atmospheric circulation is generally easy to make out, but the vagaries of winds and pressure are still in the main mysterious; notwithstanding such interesting developments as (1) the much-discussed rules of M. Gabriel Guilbert for predicting the movements of barometric depressions from abnormalities in the force and direction of the winds; (2) the systematic charting of “isallobars,” or lines of equal pressure change, associated especially with the name of Dr. Nils Ekholm; and finally (3) the hypothesis of a sharp line of demarcation between masses of equatorial and polar air along the so-called “polar front,” forming the basis of a system of forecasting that originated at the Geophysical Institute of Bergen, Norway, and has had a marked influence upon the methods of forecasters in other parts of the world.

As to the practical results of this empirical art, one point of the utmost importance is commonly overlooked by the public when it complains about the mistakes of the forecaster. He is required to make forecasts of weather day after day, regardless of the kind of map that is laid before him. Sometimes the map is so featureless (or, as the forecasters say, “flat”) that there is little in it on which to build a forecast. At other times there is an abundance of features, but they are in process of rapid and disconcerting change. In either case the ordinary day-to-day weather forecast is likely to go astray. The brighter side of this picture is that the atmospheric phenomena that count heavily in terms of dollars and imperiled human lives are not found on “flat” maps, and, when they appear on the map, generally behave in a simple, straightforward way. In other words, such events as great storms and cold waves are far easier to forecast than everyday weather, and it is the successful prediction of these events that furnishes the principal _raison d’être_ of an expensive telegraphic forecasting service.

Since weather predictions serve a variety of purposes, many different kinds of forecasts and warnings have been developed by meteorological services. In this country there are, first of all, district forecasts and local forecasts; the former, covering whole States and groups of States, being issued at a few main forecasting centers, while the latter, applying to a single town and its vicinity, are issued at a large number of the ordinary Weather Bureau stations. There is a long list of forecasts and warnings intended for special classes of the community; indeed the specialization of forecasts is carried so far that an individual citizen or a single business firm can generally obtain, by asking for it, a forecast of any specified predictable feature of the weather for a particular place. The established types of special prediction issued regularly, or when conditions warrant, include wind and weather forecasts and storm warnings for mariners; shippers’ forecasts, relating to temperatures injurious to perishable goods; aviation forecasts; “fire-weather” warnings, issued when the weather is conducive to fires in the western forests; avalanche warnings; and several different kinds of advices for the benefit of agriculture and horticulture. The United States Weather Bureau, although it is not the only branch of the Government that carries on work in hydrology, is the one charged with the duty of issuing river-stage predictions and flood warnings. An elaborate organization is maintained for this purpose, and the results are extremely successful.

The period of time covered by an official weather forecast is generally from one to two days. In this country the morning forecast is ordinarily for 36 hours from 8 a. m., and the evening forecast for 48 hours from 8 p. m., but occasionally the period is extended for an additional day. For some years the Weather Bureau has issued every Saturday a forecast in quite general terms relating to the whole of the following week. These long-range forecasts are made for extensive areas of the country, such as the North and Middle Atlantic States, the Ohio Valley and Tennessee, and the Great Lakes region. “From the weekly forecast,” says an official publication, “a farmer may know whether it is safe to cut his hay at the beginning of the week or whether it would be better to wait till the last of the week; and a produce dealer may know whether it is safe, at a particular time in the early spring, to start a carload of strawberries to a northern market.” The British Meteorological Office follows a more cautious plan. Its regular forecasts are for twenty-four hours, but occasionally, when conditions are fairly settled, announcements are made of what is termed the “further outlook.” The same office sends notices to the agricultural districts when a spell of fine weather, favorable for haying or the like, appears to be on the programme.

There are a few official meteorological establishments that have embarked on much more ambitious undertakings in long-range forecasting. The classic example is furnished by the Indian Meteorological Department, which has issued seasonal forecasts of rainfall ever since 1882. These were originally based upon reports of the snowfall in the Himalaya, abnormalities of which, as noted in the spring, appear to be related to the intensity of the subsequent monsoon rainfall. Eventually the Indian meteorologists began to seek in more remote regions for clues to the character of the Indian seasons, and they believe they have found them; the barometric pressure in South America and at Mauritius, the rainfall at Zanzibar and Seychelles, the Nile flood, and summer rains in Australia all seems to bear some relation to meteorological conditions in India.

The study of world-wide interrelations of weather, although it has not generally, as in the case just mentioned, furnished the basis of official forecasts, has engaged the attention of a great many able meteorologists. We have spoken on another page of the “centers of action” that seem to be such important indexes to changes in the circulation of the atmosphere, with concomitant fluctuations in weather. Telegraphic reports from some of these centers, including the Iceland and Aleutian lows and the Siberian and Azores highs, have helped to guide the Weather Bureau in making its weekly forecasts. Many attempts have been made to predict the weather months in advance from variations in the temperatures of the water in different parts of the ocean or from the distribution of sea ice in high latitudes. Another line of attack upon the problem of long-range forecasting is through observations of solar activities, as indicated by fluctuations in solar radiation, the prevalence of sun spots, etc. Lastly, an immense amount of energy has been expended in efforts to detect definite cycles or periodicities in the weather itself, without regard to their causes. The thirty-five year period of rainfall and temperature variations, announced in 1890 by Prof. E. Brückner, has found a place in all the current textbooks on meteorology, and several other alleged weather periods have been the subject of serious discussion.

From all of which it appears that the professional meteorologist is not at all inclined to discountenance attempts at long-range weather prediction, provided they are made both honestly and intelligently. Unfortunately the vast majority of people who, in all ages, have indulged in this sort of vaticination--and their name is legion--have been either dishonest or ignorant, or both. The world is still well supplied with them, and they are, undeniably, a thorn in the flesh of the scientific forecaster, who sometimes sees his predictions confounded with theirs by the public, and who commonly incurs the charge of jealousy and narrow-mindedness because he declines to acknowledge brotherhood with the cranks and impostors who hang about the outskirts of his profession.

Quack weather predictions are nearly always made for long periods in advance, and their popularity depends upon the fact that they give the public something--however fallacious it may be--that science does not attempt to give. The making of such predictions appears to be a particularly easy way of acquiring both fame and fortune. In this country there has hardly ever been a time when some exponent of this industry did not enjoy a nation-wide reputation. It is a satisfaction to record, however, that foreign countries produce the same sort of celebrities. Dr. Gustav Hellmann, writing in Germany, has recently published an extremely interesting account of the famous “weather prophets” of the 19th and 20th centuries. Their geographical distribution is given as follows: Belgium, 2; Germany, 36; England, 25; France, 14; Italy, 2; Austria-Hungary, 8; Russia, 1; Sweden, 1; Switzerland, 5; Spain, 2; North America, 9. The list for the United States is, to be sure, conspicuously incomplete, but we need not grieve over the fact that the fame of the American prophets omitted from the list has not spread to the Old World.

The almanac is, as it has always been, the chief stronghold of long-range weather predicting. Nobody knows to what extent the almanac prognostications are taken seriously by the public, or are meant to be by the publishers. It is to be feared that the percentage of the population that “swears by them” is not inconsiderable. Almanac publishers would undoubtedly perform a public service, and perhaps save themselves some pangs of conscience, if they would append to their weather predictions the statement that, like the portrait of the gentleman who displays his anatomy to the signs of the zodiac at the front of the book, they are published merely for the sake of keeping up an old custom, and if they would conclude every almanac with the following candid avowal, which we find in Gabriel Frende’s “Almanack and Prognostication” for 1589:

Thou hast my guess at daily weather Here present in thy view. My credit shall not lie thereon That every word is true: Yet some to please I thought it best To shew my mynde among the reste.