Pietermaritzburg Weather in August - Who is right?
Blog 024 - 18 August 2012


My son Bruce and I share several interests, such as computing in general, software development, photography, cycling and swimming. We also both seem to enjoy an argument, and so it follows that we have a lot to argue about. While we do not necessarily argue about the weather, we will occasionally argue about who best predicts the weather.

Predicting the weather can and has been done successfully done in terms of how ones grandmother's left knee is feeling. A plethora of other such and more elaborate systems also produce reasonable predictions. Ultimately it is almost always the weatherman (woman/person) who is the finally arbiter. S/he will rely on a system that is comprised of a mathematical model, a database containing records of the predicted and observed weather, and of course, the set of current data.

Computers have been useful for computational stuff for many years, and it is probably fair to say that they owe their existence to man's insatiable appetite for a faster computational device. Charles Babbage, one of the forebears of modern computers, also wanted more accurate computations. He was appalled at the inaccuracies in the tables used for navigating and gunnery. Not a coincidence that these are also used by the Navy/Military. Otherwise where would the very large sums of money for research in these endeavours come from? Returning to the tables, they were prepared by mathematicians who designed the computational processes, and human "computers", who did the computation (primarily adding and subtracting).

Computing devices have over a relatively short space of time, also generally become much smaller, cheaper, powerful, and ubiquitous. They however still have computational limitations in terms of some of the problems we would like to solve. One of these hitherto intractable problems, has been the prediction/simulation of the weather in real time on a global scale. This problem will shortly be addressed by the seminar at the Isaac Newton Institute for Mathematical Sciences. (Blank cheques in favour of my attendance, always welcome!) This page on the World Meteorological Organisation site, is also a good read.

So I guess we can forgive the South African Weather Service and Weather Underground if they get the predicted weather for Pietermaritzburg over the week in question wrong. As the day of this week pass, I will record the observed maximum and minimum temperatures here for the record. I will also continue to use their services, especially the South African Weather Service's myLife weather log for cycling. This service provides indications of how the various weather elements will vary during the week ahead, specifically within the context of cycling.

So here are the weather predictions for Pietermaritzburg for the following week as provide by the South African Weather Service and Weather Underground respectively:



And here, except for Sunday, are the observed temperatures for Pietermaritzburg as report on each of the corresponding days in The Witness:

Fri  Sat  Sun  Mon  Tues Wed  Thur
16 / 9 25 / 8 32 / 12 29 / 17 18 / 15 20 / 14 17 / 14

What should be done now, is to determine the extent to which the predictions of the two weather services correlate with that which was observed. I will attempt to do that this evening. Until then, I will stick my neck out, and suggest that the South African Weather Service will produce the best correlation results.

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