WEATHER FORECASTING

Waipa Post, Volume 52, Issue 3705, 10 January 1936, Page 10

WEATHER FORECASTING

AN IMPORTANT ADVANCE. Judging by the tone of recent discussions in Melbourne on the subject of weather forecasting there are many in our midst who regard the predictions of official meteorologists as having little more probability of truth than could be obtained by the toss of a coin—heads it will be fine, tails it will be wet.” Actually, the best official forecasting of the present day attains more than 80 per cent of successes, though it must be allowed that there is no unambiguous rule for deciding between success and failure in doubtful cases. It must also be acknowledged that, for a 24 hour forecast, guidance by the maxim “To-mor-row will be like to-day,” combined with careful consideration of the familiar portents of cloud, wind and sky might give results as good as those which the professional forecaster can achieve with all his resources—especially if the forecaster is shrewd enough to avoid prediction in doubtful circumstances. It is because the Weather Bureau cannot allow itself this convenient option that it must occasionally—as it sometimes does —forecast the direct opposite of the event, knowing full well that the choice lay between closely balanced alternatives. It is, even theoretically, possible to place the business of weather prediction on a scientific basis, so that the course of the weather can be predicted with a precision and certainty approaching that with which astronomers can foretell an eclipse of the moon! BODY OF EXPERIENCE. If the changes from day to day in atmospheric conditions are comparable with the development of a bush fire, then, of course, anything like exact prediction is an impossibility, and the best that could be done would be to build up a body of experience concerning the customary sequences occurring in the weather, and make predictions on the basis of these, much as decisions in the law courts are made on the basis of a body of precedent. This is, in fact, very much what has been done, in weather forecasting.

Information concerning barometric pressure, air temperature and humidity, wind velocity and direction, is collected from stations distributed over as wide an area as possible. These observations are then collated by the officers, and represented on the well known synoptic weather chart on which are drawn the isobars, lines connecting places of the same barometric pressure. The vareties of weather associated with the more usual types of weather maps are now so well known that predictions as to the next day’s weather can be made,, as stated above, ,in most cases with a fair degree of certainty, though it must be allowed that the cyclone—the low pressure area, which is the most Important weather type in southern Australia—has a most disconcerting tendency to wander from its orthodox and proper west-east route into latitudes unknown. IMPORTANT ADVANCE. The most important advance in the methodology of weather prediction in recent years lies in the recognition of the important part played by the movement of large bodies of air—“air masses”—which tend to preserve their identity and characteristics as they drift over the surface of the earth. In the temperate zones these drifting air masses fall into two main types, the “polar” and the "tropical,” the former, hailing from highter latitudes, being composed of cold, dense and generally dry air, while the tropical air masses are, naturally, warmer and more humid. In fact, no expert knowledge or instrumental equipment is required to discriminate between these two kinds of air. Our “weather sensitivity”-—to adopt a German term —is amply competent to make us aware of the presence of the one or the other, the warm, enervating tropical air generally preceding a weather disturbance, while the colder, invigorating air follows in its wake. The region where two air masses of different constitution meet constitutes what is termed a “front.” The word has an obvious military implication, and a “front” is indeed a battle field, where the forces of the air engage.

The introduction of the “front” as an element in forecasting was made by Norwegian meteorologists during the war, when, deprived largely of the meteorological data received from other countries, they sought compensation from other countries by instituting more numerous and intensive observations within their own country, and thus discovered the great importance of these boundaries between large bodies of air in causing rain or snow.

For v-hen a body of warm, moist air encounters a colder, denser mass, it tends naturally to rise and flow over this into regions of reduced pressure where the consequent expansion and cooling cause condensation and precipitation of its water vapour. CYCLONES.

The cyclones which are so typical a feature of our Australian winter weather are explained by the Norwegian, Bjerknes, as great vortices which tend to develop out of waves in the boundaiy layer between the air masses. The formation of vortices in such a “surface of discontinuity” between moving bodies of fluid was actually discussed by Melmholtz nearly 100 years

ago. They can be observed where a stream of flowing air passes through still air, as in the air from a chimney or even from a lighted cigarette. The cyclone, once formed, is a meteorological entity which maintains its identity and character as it travels along (the late Mr C. Wragge even gave each one a classical cognomen); and its course, with the associated changes in wind direction, temperature, barometric pressure and rainfall can, as a rule, be traced in advance. A “front” devoid of these cyclonic whirls requires more numerous observations of the meteorological elements to define its progress and anticipate its probable development, and it is this necessity to multiply the number of observing stations and the frequency of observations which, at present, constitutes the most serious obstacle to the adoption of this system of weather analysis and forecasting in Australia. In comparison with Europe we are at a further disadvantage in being unable to secure reports from stations to the south and west, from which direction the polar air masses invade our continent. But even in Europe, with its far more numerous and better distributed observing stations—l believe that there are now no fewer than six stations within the Arctic Circle sending regular reports—the adoption of this method has not resulted in anything like 100 per cent of accuracy in forecasting. PESSIMISTIC OUTLOOK. Is there no prospect, then, of the attainment of practical certainty even in respect of 24 hour forecasts? Authoritative opinion on this point seems rather pessimistic, taking the view that any radical advance must await the discovery of a more thorough working out of the physics of the air, and especially, of course, of the problems associated with weather types and changes.

But some look hopefully to the rapidly increasing knowledge of the upper air, and believe that if daily observations of its condition could be secured from a sufficient number of stations, a great advance in accuracy of prediction would result. Von Ficker, a German meteorologist of note, even argues in a recent article that it is in the stratosphere that the causes of lower air movements must be sought. If this be so, it is to be feared that many years must yet elapse before the desirable improvement takes place. For, although the stratosphere can be explored and its temperature, pressure and humidity ascertained by self-recording instruments carried on pilot balloons, these instruments are not always recoverable, or if recovered, come back too late to be of use in forecasting the next day’s weather. The Soviet Meteorological Service—which, is now issuing synoptic charts hot only of Russia, but of the whole northern hemisphere—has succeeded in equipping its balloons with a wireless transmitter, which automatically broadcasts the desired information as to upper air conditions. Of course, if the projects which have been mooted of long distance stratosphere flights by aeroplane are realised, this would add a further valuable source of information to meteorological science.