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Chapter 10

Be Weather-wise

The next suggestion for getting the most from kites is to focus one's attention on an important subject—the weather. The close connexion between kite flying and the weather is apparent to the most casual observer. There are days when conditions are ideal; there are days when they are fairly good; there are days when they are bad. And there are times when the weather varies from hour to hour. A day which seems to be promising at the start does not keep its promise; and one which might not look too good at first turns out to be better than was expected. Because of this changeable weather it is really necessary to have some understanding first, of the kite itself—particularly of making adjustments in different flying conditions; and second, of the weather, which is the immediate subject. And let it be said that to understand the weather does not imply that one must be an expert in meteorology. All that is contemplated is a working knowledge that will help the kite flyer to get the most from his hobby. The aim in this section is to point out some of the ways and means whereby this knowledge may be gained. One way is to study the clouds.

Clouds

The reader may often have noticed their changing pattern as they move along. This panorama is one of the wonders of nature— a fascinating scene wherein every cloud is subject to change, and no two are identical, and some combine in form. Yet, although there is this state of flux, clouds are classified and names given to them. True, it is not always easy for the amateur to place them in the groups to which they belong. But in due course, by sustained observation, he may be able to do this. A guide in such study will be found in the list of the ten main types of cloud, printed below, as given in the International Cloud Atlas.

Classification

1.	CIRRUS, 'detached clouds of delicate appearance, fibrous structure, without true shadows, usually white in colour'.
2.	CIRRO-CUMULUS,  'small rounded masses or white flakes without shadows, arranged in groups or lines, or sometimes in the form of ripples such as those formed on the seashore'.
3.	CIRRO-STRATUS,   ‘thin veil   of whitish cloud, sometimes entirely diffuse and giving the sky a milky appearance, sometimes showing a fibrous structure'.
4.	ALTO-CUMULUS, 'rounded masses or discs, more or less large, arranged in groups, in lines or in rows, following one or two directions and sometimes so crowded together that their edges are joined'.
5.	ALTO-STRATUS, 'a veil of a colour more or less grey.
6.	STRATO-CUMULUS, iarge, lumpy masses or rolls of dull, grey cloud frequently covering the whole sky and sometimes giving it an undulating appearance'.
7.	STRATUS, *a uniform layer of cloud, like fog in appearance but not lying on the ground*.
8.	NIMBO-STRATUS, 'a low layer of structureless and rainy-looking cloud, sombre grey in colour'.
9.	CUMULUS, 'thick cloud whose summit is dome-shaped and exhibits protuberances, while the base is nearly horizontal'.
10.	CUMULO-NIMBUS, 'great masses of cloud rising in the form of mountainous towers of which the upper parts, of fibrous texture, sometimes spread out in the form of an anvil.

Clouds occur at different heights, and this fact is indicated by the use of the prefixes, cirro and alto. Cirro denotes those which are between 25,000 and 35,000 feet up; and alto those between 10,000 and 25,000 feet up. The lower layer occurs mainly between 500 and 7,000 feet up (Nos. 6-101

Clouds and Weather

Generally speaking, the higher the clouds, the better the weather is likely to be; the lower the clouds, the worse it is likely to be. In particular, three factors to be taken into account are: movement, change and colour. The following are examples of these. Small cirrus clouds—'mare’s tails’—when they thicken and become lower, are a sign that rain is on the way. Cirro-cumulus—'mackerel sky'—heralds the approach of rain, and on occasions, of thunder. Cumulus clouds, when they expand early in the day, are also a warning that rain will fall later. Cumulonimbus becomes 'the thunder-cloud' when its top at the front becomes extended so that the whole cloud looks like an anvil. This may be accompanied by a sudden cool breeze, which travels in an opposite direction to that of the actual wind at the time. The cloud and the breeze are signs that a storm is about to break.

Clouds, however, are not only associated with rain and storm. They may also indicate fine weather. As an example there is the cirrus, previously mentioned, which now appears in a more promising role? If it does not thicken and seems to be at a standstill or only moving slowly, in a region of high pressure, then it means fine weather. The 'fair weather cumulus' is another example. It does not grow bigger, has no marked upward bulges and moves slowly along. These are the clouds, which are often to be seen on a warm summer day.

In the list and the examples given, colour is associated with changes in the weather. It ranges from the white of cirro-cumulus to the dark grey of nimbo-stratus. The association is shown in further instances of sky colours, the first of which occurs in the old saying:

Red sky at night, shepherd's delight
Red sky in the morning, shepherd's warning.

It has been estimated that this is true about three times out of five. The second illustration adds another colour to the range: yellow. A watery yellow sunset is a sign of coming rain; a bright yellow sunset is a token of an approaching high wind. Again, a golden ring round the moon is a warning that a storm is on the way. In the last place, there is the rainbow. This multi-coloured arc appears opposite to the sun, and is formed by refraction and reflection of its light through falling raindrops. If the sun is in the east, and the rainbow is in the west and a west wind is blowing, then rain is moving towards the observer. If the sun is in the west and the rainbow is in the east and a west wind is blowing, then rain is moving away from the observer.

Clouds then are an index of weather changes; and so is the wind, which we now consider.

Wind The subject is of immediate interest to the kite flyer, for the wind is in turn both his friend and his foe. He cannot alter this fact, but he may gain some knowledge of these different moods, which may stand him in good stead. Under this heading brief comment will be made upon each of the following items: first, wind and weather; second, estimating wind direction; and third, estimating wind speed.

Wind and Weather

As far as the British area is concerned, a general statement may be made: southwesterly winds are wet winds; northeasterly winds are dry winds.

The southwesterly winds which have travelled hundreds of miles across the Atlantic have taken up a great amount of moisture on the way. When they encounter the main highlands of the area, they are forced to rise and in so doing the greater part of the moisture is squeezed out as rain. On the other hand, north-easterly winds when they prevail for a time, are usually a sign of an anticyclone over the North Sea, or even farther north-east, and anticyclones are associated with spells of fine weather.

(Additional notes on depressions and anticyclones are given at the end of this chapter.)

Estimating Wind Direction

A simple method is to wet a finger and hold it up; the side which feels cold first is the windward side. Another way is to observe the direction in which low cloud or smoke are moving. If these are not present, as an alternative, a handkerchief may be held up to flutter in the wind. By these means the operator can judge the kite's line of flight, and so will be able to guard against any possible obstructions, such as trees or overhead wires.

Estimating wind direction is also useful in making forecasts and flight records, which are described below. In these cases a weather-cock and a pocket compass are the best guides. If there is no local weather-cock, the reader might be interested in the making of a simple type, as shown in Chapter 7. On-the-spot wind checks are carried out with a compass, and it is used in conjunction with the tests mentioned in the first paragraph. When the compass is held horizontally in the hand the needle points to the magnetic north, which is not the exact geographical north. The slight variation must be ascertained in any given place in order to find the true north. For example, in England the compass points about 8 degrees west of geographical north.

Estimating Wind Speed

The Amended Beaufort Wind Scale, printed at the end of the chapter, is valuable for this purpose; as also is an anemometer. The Wind Scale was formulated in 1805 by Admiral Sir Francis Beaufort for measuring the velocity of the wind and since then has been periodically revised. An anemometer is an instrument for registering the speed of wind. Instructions for making and using a simple type are given in Chapter 7.

Estimates of wind speed are important for two reasons. In the first place, speed and strain are closely connected. For example, if wind speed is 5 m.p.h. and it increases to 10 m.p.h. then its strength intensifies and the strain on the kite increases. The strain becomes more pronounced as the kite climbs higher. Consequently, there is a stronger pull on the kite line.

The larger the kite the more do these considerations have to be borne in mind. In the second place, wind speed is a factor to be noted when making weather forecasts and flight records, which are now suggested.

Weather Forecasts

It is recommended that one's own forecasts be made on the basis first, of official forecasts, which are given on the radio and television and in the daily press. These general forecasts may be compared with regional forecasts, where they are given. The amateur forecaster should also take into account certain factors in his own area. These might have a bearing upon local weather conditions. For example, where there are hills and woods they act as a shield against the wind for those who are sheltered by them. A valley may cause the wind to change its course to some degree and perhaps increase its force. Again, a warm moist wind may move over flat country accompanied by only light showers. But when the wind crosses hilly country considerable rain may develop. The amateur weatherman studies the area in which he lives, notes its physical features from the point of view that they may have some connexion with the local weather.

Official forecasts and reports in the press are often given together with weather maps. In order to understand the maps the following things should be noted. The positions of weather stations are indicated by small circles, and barometric pressures by numbers. Places which show the same pressure are linked by lines, called isobars. These run near to or might even pass through the stations. Wind direction is indicated by arrows. To these arrows lines may be added representing wind speed. (Refer to the Beaufort Scale for map symbols.) Again, wind speed may be indicated by numbers. Note that for a depression the arrows are turned slightly towards the centre of pressure, and they point in an anti-clockwise direction. For an anticyclone the arrows point outwards from the centre of pressure, in a clockwise direction. When one is looking at a weather map the relative positions of the isobars should be noted. If they are drawn close to one another then wind speed is greater than when they are farther apart. One other thing may be mentioned, namely that among other map symbols which are used are those which represent a warm, a cold, or an occluded front.

On the basis of such official forecasts, plus one's own observations, an attempt may be made to estimate what flying conditions will be like one, two, or more days ahead. As far as local observations are concerned, it is a good plan to make them at fixed times during the day, for example, say 8.30 a.m. and 5.30 p.m. This would provide a regular system for weather study, whereby the following items could be recorded: wind direction and speed; cloud formation; temperature and barometer readings. On the latter point, it will be remembered that a falling barometer is a sign of rainy weather, and a rising barometer, of fine weather.

Flight Records

Much pleasure is to be derived from making these and from keeping them for reference. The idea is to set down in a note-book certain comments relating to flights as they are made. The records will be mentioned again in connexion with kite clubs and competitions. In the meantime, the following gives an idea of the kind of thing in mind.

Flight Record Date of Flight.
Base (i.e. place where kite is flown).
Cloud Formation (see list of cloud types).

Base Maps

These have not been previously mentioned, and the suggestion is now offered for consideration. It is assumed that the reader does not invariably fly his kites in one place. There might be half a dozen or more favourable sites in his locality, which could be indicated on a map, covering a radius, say, of five miles. An Ordnance Survey Map would be useful in this project. It may be that one could be studied at the local library. There is a series of these maps on a scale of six inches to the mile, which contain a great amount of information. The best-known series are on a scale of one inch to the mile. With the help of one of the above, a map could be drawn on a large sheet of paper, marking for example, prominent buildings, roads, fields, hills, woods and water in different colours. As bases were found and tried they could be marked on the map, and notes on them added at the bottom of the paper. Or they might be classified according to merit as one star (1*), two star (2*), and so on. Such a means of reference would be invaluable if a club were formed and competitions were held. The latter are the subjects of the next chapter.

Depressions and Anticyclones

hese notes offer additional information about the British weather, and may be found helpful in the following of official forecasts, and in estimating flying conditions beforehand.

Depressions are storms bringing wet weather. In form they are roughly oval, and sometimes measure nearly 1,000 miles from end to end and perhaps 200-300 miles across. They begin in the neighbourhood of Newfoundland, and move from west to east across the Atlantic, travelling along regular paths, according to the seasons. In summer the path lies farther north than it does in winter. The speed of travel varies. It may be sometimes about 700 miles per day. At other times one may be at a standstill for a few days. As to duration, generally speaking a depression originates and fades out within the space of one week. On an average 50 depressions move across the British Isles in a year. They occur more often in winter than in summer.

A depression is also defined as being a system with low pressure at its centre, from which pressure increases in all directions. The air at the centre is warmer than the air surrounding it, because warm air is not so dense or heavy as cold air, and consequently it exerts less pressure. The wind blows spirally towards the centre in an anti-clockwise direction in the northern hemisphere.

Certain signs herald the approach of a depression: a falling barometer, a southerly wind, a cloudy sky, and at night perhaps a halo round the moon. As the centre of the depression moves nearer, the wind may drop, the clouds become lower and threatening, and rain falls—light and scattered at first, but developing to heavy and continuous. When the storm centre has passed, the barometer gradually rises, the wind may change to northwesterly, low stratiform cloud and drizzle give way to clearing skies and sunshine. The depression gradually fades out over north-west Europe.

This description applies to a depression only in a general way, because actually no two are identical. There are variations of the general pattern, and therefore the unexpected can happen. Again, a given area may not be in the direct path of the storm centre, but to the north or south of it. In these cases there could be variation of rainfall and of wind direction.

In contrast to a depression, an anticyclone is associated with fine weather, warm to hot in summer and clear and frosty in winter. These periods of fine weather might last for days or even weeks. However, as will be seen in a moment, this is not all, which may be said about anticyclonic conditions.

An anticyclone is a system in which the centre of high pressure is encircled by low pressure. The winds blow outwards from the centre in a clockwise direction. They are usually gentle winds. Anticyclonic weather varies according to the position of the centre of pressure. If it is over the British Isles in summer, then there will be summery weather: clear skies, light winds and warm to hot days. In winter it might lead to dull or foggy conditions.

If the centre lies farther north, off the western coasts, mixed weather would be the result, with bright intervals, scattered showers, winds north to north-west and perhaps temperatures below average for the time of the year. If the centre is to the south of the British Isles, then the weather is likely to be mild and humid, with cloudy skies.

There are periods when neither depressions nor anticyclones prevail. This is called unstable weather, with local developments of threatening skies, rain and perhaps thunder. In winter, unstable weather might result in cold north winds, sleet and snow.

In weather reports, among other terms, which are used, there are fronts and troughs. At a warm front associated with a depression the warmer air is forced upwards and over the underlying cold air. As the warm air rises, it cools and some of its water vapor forms into clouds producing a wide belt of rain, which moves ahead of the front. In the case of a cold front, the heavier cold air meets and pushes under the warmer light air. This action leads to the formation of towering clouds, showers of rain and sometimes thunderstorms, which arrive not ahead of but at the same time as the front.

There are times when by the action of the heavier cold air the lighter warm air is lifted completely off the ground. The front is then called occluded, and since there is no warm air at ground level, there will be no rise in temperature as it passes. Many of the depressions moving over the British Isles are partially or completely occluded.

Sometimes one will see on a weather map that, instead of being drawn in a rounded pattern, the isobars (lines of barometric pressure) are joined at sharper angles. These represent a trough, which is a V-shaped depression. Troughs may have warm, cold or occluded fronts. A warm front brings cloudy warm wet weather; cold or occluded fronts, heavy rain followed by better weather.

The Amended Beaufort Scale

 

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