I’ve got into the habit of recording the temperature of each ride and noting what clothing I’m wearing, this helps me guess what clothing I’ll need but also gives me some statistics of what clothes are doing the mileage. I naturally also record the mileage, this gives me an idea of when certain maintenance activities (e.g. Rohloff oil change) are due.
I can see I wear cycling shorts more than any other item of clothing and only at temperatures above about 9 celsius. Anything lower and I need leg warmers, anything below freezing and I opt for roubaix tights. So if the forecast is minimum 12 degrees celsius then I know I can ride comfortably in shorts.
(In the UK) The Met Office has a good website for checking the weather and it also has 24hrs of observations under the “Latest/recent” section. This is my primary source of temperature statistics, yes it’s not as accurate as carrying a thermometer and recording the temperatures myself, but that would be OTT wouldn’t it 🙂