I’ve built a new page for forecasting indoor humidity:

https://www.richard-stanton.com/humidity-forecast

This is similar in concept to the Humidity Calculator.

We use a UK postcode to make a request to the BBC’s weather forecast. We then use the same maths as the previous humidity calculator to get the inside humidity. We assume the inside temperature is a constant 21C. This allows us to see how the absolute humidity is changing throughout the coming days. As such it can help to keep indoor humidity to a minimum.

It’s built in javascript and uses jQuery/AJAX to do the requesting of data. The plot is built with plotly.js.