I'm not too sure tbh, I just looked at Google.Our forecast (tomorrow.io) and their ClimaCellV4 API doesn't show as much rain as... uhm, accuweather? I guess Jimmi (still he who runs it, right?) and myself uses two different weather apps and API's. There's a couple of reasons why I like ClimaCell and tomorrow.io, one of them is the forecast-probability!
"forecast is used in cloud roll in/out mode to get in clouds before rain happens (Note: Only climacell API!). That means if forecast tells the client that rain will happen next 40minutes with a cumulated duration of some time, cloudiness is set to 100%. The forecast poll is done every 10min."
Which we noticed yesterday in the Road Atlanta race. It varied quite a lot with cloud cover.
"The client will take the probability into account in some situations. If so, it triggers by a probability controlled random algorithm whether rain is happening or not."
So, from what I've read is that a probability that's under 25% will not give rain. Probability over 75% will give rain, while between 25 and 75% will follow some witchcraft algorithm to decide.
Then again, it's only "in some situations" and may be overridden by sudden new real life weather data.
It sends out a call for new weather information every 3rd minute, and then the new weather is delayed 1min before it's applied on the server. This to allow some sort of transition. So if it goes from rain to no rain it gradually goes away during that minute instead of just stopping abruptly!
It's way to techy for me to understand how it properly works, but it works really well so I don't care!
I'll definitely be more than happy if it isn't raining that much, did do some testing last night though and it wasn't as bad as I was expecting in the wet. I'll still feel much happier in dry conditions though.