56- WEATHER FORECASTING. 



coast, Cape Agulhas, Cape St. Francis and Port Elizabeth ; for 

 the south-east, East London only ; while for Eastern Transkei 

 and Natal, Durban has to suffice. Until recently Port Nolloth 

 used to supply readings, these were temporarily suspended, but 

 have now been resumed ; this station is situated in the north- 

 west district, for which forecasts are not issued. 



And yet from such meagre information much has been 

 gleaned, and we have now a fair knowledge of the motions 

 and forms of areas of low and high pressure, and it is possible 

 to forecast weather with a degree of certainty out of all pro- 

 portion to the data. We live in the hope of seeing more 

 observing stations instituted and more extended information 

 supplied from each. Since the 15th of April this year 

 the morning forecasts embrace the Transvaal and the northern 

 portion of the Orange Free State, this area being divided into 

 districts 5 and 6. 



The procedure adopted for issuing these forecasts is as 

 follows: At all the stations enumerated, except from Transvaal, 

 pressure, temperature, wind and rainfall observations are taker 

 at 8.30 p.m. and 8.30 a.m. ; Transvaal observations are taken 

 at 9 a.m. only. Between 9 and 10 a.m. these are wired in code 

 to the Meteorological Office in Cape Town, where they are 

 decoded and entered in a book. From this information the 

 forecaster complies two weather charts, one for the evening 

 and one for the morning. Then he has to study the distribution 

 of pressure, direction of winds, temperature changes and so 

 forth, and with the experience of his past investigations to 

 guide him, he can see what the synoptic conditions prefigure 

 in the way of weather changes. The forecast is then written 

 out for the six districts and a copy thereof is attached to a 

 notice board at the office for public inspection, and is wired tc 

 various places in South Africa. The word forecaster is men- 

 tioned, but in fact there are at present two, one with Cape 

 Province experience and one with a knowledge of Transvaal 

 weather. 



Each prediction is verified on the following day, and once 

 a month the percentages of successes or failures are worked out 



Thus far the routine work ; we will now consider forecast 

 ing itself. 



Atmospheric pressure is taken to be that at sea-level, and 

 for this purpose each reading has to be corrected for instru- 

 mental error and temperature, then reduced to that plane. Tem- 

 peratures are not so reduced. 



When studying an isobaric chart the main points to be 

 noted are the positions of the areas of high and low pressure, 

 as well as their shapes. Pressure is the most important element 

 in forecasting, although, of course, other phenomena have their 

 values. 



