THE SEVERE WEATHER AND THE FORECASTS.
THE weather changes of the last ten days have been so marked as to have compelled the attention even of those whose interest in meteorology seldom extends beyond the forecast for the current twenty-four hours. A reference to the recent warnings and forecasts issued by the Meteorological Office, shows that in wintry weather the unusual is not always the unexpected, and that changes which seem curiously sud- den to those unfamiliar with the observed facts of storms, are not necessarily capricious. Owing to the position of our islands on the west Atlantic fringe of Northern Europe, English weather is more shifting and uncertain than that on the east coast of America, for instance, and than that of Central Europe. Our storms are seldom allowed to do their work without interference by " secondary " or conflicting depressions ; they are crowded and jostled by other storms, and not allowed to finish their course according to rule. When our weather does exhibit any strongly marked features, the natural assumption is that what is unusual in our ex- perience is a deviation from the ordinary laws. It would be safer to assume the exact opposite. The weather of the last ten days is, in fact, a very good example of the normal course of things when the sky above the British islands is clear of intruding "depressions," and a cyclonic storm is allowed to pursue its natural course. In proof of this, we may point to the accuracy of the forecasts made in the Meteorological Office, before and after the thunderstorm which rattled among the spires of the churches from Westminster to Fleet Street on January 23rd, and was regarded, quite wrongly, as an abnormal phenomenon. The approach of the cyclone in which this electric discharge had its proper place was known on the previous evening. "A new and apparently deep depression is advancing towards our northern districts from the north-west, and is likely to cause very rough weather over our islands to-morrow," was the warning issued, and the storm-signals were hoisted all round the English, Scotch, and Irish coasts. The storm centre was far to the north of Cape Wrath ; but though the English meteorologist has no outposts in the far Atlantic, the symptoms of its approach were duly marked, and its subsequent effect upon the weather was a matter, not of conjecture, but of the modifi- cation of the general features of a cyclonic storm by particular circumstances. What followed was mainly remarkable for the rapidity with which the usual sequence occurred. The thunderstorm of Wednesday, January 23rd, was only a part of the weather which may be expected with a cyclonic storm. To us, standing at a fixed point on the ground, these storm phenomena appear as a series of changes, partly seen, partly felt, and not necessarily or obviously con- nected. If the whole could be shown in miniature on a portion of the sky, which could all be seen above oar heads at the same moment, its appearance would be somewhat as follows. The front of the storm would appear as a black mass of clouds, sliding forwards across the sky, with a curved rim like the edge of an oyster-shell. From this mass the wind, which we cannot see, and can only determine the direction of by second-hand reports, would be blowing in a direction roughly coinciding with radii drawn from the hinge of the oyster- shell outward through the front edges, but with a twist towards the right. As soon as the centre has passed, the clouds break to the right, and on that side the weather clears after showers, and in winter a dry north-west wind follows. The suddenness of the advance of the black cloud was the most marked feature of the cyclonic storm of the 23rd. But the storm was also so concentrated and ran through its changes so rapidly, that it may be well referred to for further illustration of cyclone weather. According to Mr. R. Scott's " weather charts and storm warnings " the changes which may generally be expected in case of such a storm passing London are as follows :—" We shall experience first the phenomena belonging to the front of the system ; the appearance of cirrus clouds (mares' tails) in the sky, then the south- easterly winds, the great rise of the thermometer, the sky becoming gradually overcast, the wind veering through south to south-west, and rain falling steadily." All these phenomena were on January 23rd crowded into the space of some three-quarters of an hour. There was a rapid thaw between 8 a.m. and 9 a.m., a southerly wind, a drift of " mare's tails," sudden darkness, and heavy rain.
But the mischief of such a storm lies rather in what follows than in what precedes or accompanies it. "As soon as the wind passes the south-west point, and draws to the west or north-west, the barometer begins to rise, often with a sudden jump, and the temperature falls, often with a heavy shower of rain, possibly turning to hail with a thunderstorm, after which the air becomes much drier, and the sky clears with a north-west wind. After such disturbance as this, we have frequently a sharp frost at night," &c. One other common feature of these storms is a sudden shift of wind, which takes place between south-west and north-west, with a heavy squall and snow-shower, and an instantaneous fall in tem- perature. Mr. Scott quotes an example in which this shift of wind (at Kew) was accompanied by a fall of tempe- rature of six degrees in thirty minutes. " It is also a remarkable fact," he adds, "that at the moment of this sudden change of temperature, the condition of atmospheric electricity changed from negative to positive." The sudden massing of the clouds, the electrical phenomena breaking out in a thunderstorm of strange violence, and the furious wind-squalls following, each in its due place in the series, but with great rapidity, make this particular storm a natural meteorological object-lesson. From the first ad- vance of the cloud-rim, through the period of dark- ness, to the outbreak of the thunderstorm, less than ten minutes passed in the Central London district. The thunder began at 9.50 a.m., and lasted for seven minutes. In this time there were seven peals of thunder, one of which lasted for twenty-nine seconds, and all the flashes of lightning were within a radius of a mile, and three church-steeples were struck between Westminster and Fleet Street. Then, according to rule, the barometer rose, the temperature fell five degrees, and the furious squalls followed with a sudden shift of wind, and a hailstorm. During the quarter of an hour in which the gusts blew, more damage was done than by hours of steady gale. The weather then became dry, clear, and frosty ; but the wind which circles round the cyclonic centre rose with violence, and by 2 a.m. on Thursday morning the 'Escurial' was wrecked off the Cornish coast, and ten men perished in sight of the shore. " After the storm a calm " would, in modern meteorology, be interpreted, " After the cyclone an anti-cyclone ; " that is, a period, usually lasting for some time, in which the air flows out from the centre, in place of flowing in, as in the case of the cyclone, while its place is taken by other air dropping from above. The winds are light, the weather dry, and in winter very cold, and though there is no rain, there is often a frost-fog, because accumulated vapours are prevented from rising by the general descent of the cold air from above to take the place of that flowing out of the sides of the anti-cyclonic area. These cold, still anti-cyclones usually last some time, and the approach of a cyclone is usually preceded by ample warning in the shape of a change of wind. An anti-cyclone means good skating weather, which usually lasts, and in this, again, the experience of the past week has justified the rules. The anti-cyclone, or skating weather, began on Saturday, and lasted without a break until Wednesday, when the existence of "a large anti-cyclone spreading from the south-east" was announced. It is interesting to note that the " most marked characteristic of anti-cyclones is their permanence." What skaters, tobog- ganists, and sleighers must therefore most earnestly desire is the appearance over our island of " an anti-cyclonic area of high pressure " following a series of cyclones, and that is exactly what they have for this week been permitted by the clerk of the weather to enjoy. When the inevitable thaw does come, it will probably be preceded by a warning of the arrival of a fresh centre of depression in the Atlantic, moving from west to east. The issue of the warning will be followed by a change of wind, probably to the south-west, and if this is accompanied by a steady rise in the thermometer, it is probable that the anti-cyclone period is at an end, and with it the skating season of 1s95.
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