WEATHER FORECASTING. 6?, 



Ocean cyclone is affecting Natal and the Transkei. As an 

 example the blizzard of the 31st of May, 1905, may be men- 

 tioned. The chart for the 30th indicated low pressure all over ; 

 the monsoonal tongue was narrow and bounded by the 29.90 

 isobar, a low was over the south-east ocean, and a " sub " over 

 Basutoland. Pressure was increasing rapidly to the south-west, 

 but falling elsewhere; gradients were thus getting steeper. That 

 day rain was general over every District, and snow fell at all 

 high stations to the east and north-east of the Cape, including 

 .Basutoland. On the 31st a high anti-cyclone was over the west 

 and south, moving rapidly eastwards ; at the same time pressure 

 had decreased considerably over the north, north-east and Natal ; 

 at the latter place a depression from the Indian Ocean increased 

 the intensity of the weather. The monsoonal tongue was now 

 very low, and the " sub " over Basutoland was bounded by the 

 29.85 ins. isobar. Very cold and strong winds prevailed, and 

 snow continued to fall over the high lands to the north-east, 

 including Basutoland. A blizzard swept across Upper Transkei 

 and Natal, doing much damage. 



Owing to the distribution of high and low pressure during 

 the winter months secondaries have their steepest gradients to 

 the north, so that the storm and rain bringing area is central and 

 to the north thereof. They thus have a tendency to increase 

 the rainfall, or even to bring unexpected rain when no indications 

 appear of it on the chart. With our present limited knowledge 

 it is impossible to forecast the appearance of a secondary, but 

 when one is seen it can be dealt with by bearing in mind that the 

 core is always a circular area where rain is almost constant ; 

 this area extends towards the region of higher pressure, and 

 intensifies the existing rainfall. Towards the region of lower 

 pressure weather has a tendency to clear temporarily and winds 

 to get lighter. Thus by knowing the general distribution of 

 pressure within which secondaries exist, we can foresee what 

 the results will be. 



Generally. 



There are other forms which isobars assume beyond those 

 enumerated, but, as far as the Cape Province is concerned, they 

 have not been studied to the same extent. The Wedge is a 

 very common form ; these extend from all points of the compass, 

 but in each case the extreme point is termed the Crest, and here 

 thunderstorms are to be looked for during summer. Along 

 the centre of the wedge fogs are to be expected, but these are 

 not always certain away from the coasts. A wedge occurring 

 between two depressions will cause a sudden clear up when 

 indications have existed for rain, so that if such a sudden 

 clear-up occurs, look for the appearance of a following de- 

 pression. 



Between two areas of high pressure or two of low there 

 is an intermediate region called a " Col," and in such a region 



