A Zambretti weather forecaster

When I was recovering from my stem cell transplant last year, I built a weather forecaster. It uses a Raspberry Pi, a BME280 sensor and a 20×4 character LCD screen. The forecasting algorithm I’d written for it was rudimentary, to say the least. However, earlier on this year I came across a device known as a Zambretti forecaster. These were made by Negretti and Zambra for the UK market in the 1920s.

The Zambretti device uses air pressure, the direction of change, season and wind direction to make a forecast. Depending on what you believe on t’internet, a forecast accuracy of 90% is possible. You can buy replicas from a popular forest-based e-commerce site if you want to. I didn’t, but with the help of a search engine and a number of people who’ve been down this route before, wrote my own Zambretti forecasting algorithm. In FORTRAN 77 naturally.

The results so far have been encouraging. However, I’m of the opinion that the accuracy I’m perceiving may be due to the Forer effect, rather than the goodness of the algorithm. It’s true that different barometric conditions do produce different forecasts. However, I remain unsure as to the real difference between Fine : showers possible, Fair : showers likely and Fairly fine : showers. Not much I suspect.  

Anyway, it was producing good enough results to invest a few more pounds in a second LCD display. This retrieves the forecast made by the Raspberry Pi and sensor covered in cobwebs in the garage and displays it in more comfortable surroundings. This time I’ve stuck to C as my language of choice.

Raspberry Pi 4B plus a 20x4 LCD screen showing a Zambretti weather forecast
A Raspberry Pi 4B plus a 20×4 LCD screen, showing a Zambretti weather forecast all the way from my garage.

The code for my v3.0 Zambretti forecaster with remote display screen, with instructions, is available on github. Some (most) of the code could definitely do with improvement …

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