looking for a bit of help in a forecast calculation

Hi all. I have run WD over the years and also combined WXsim etc at various locations and have in previous years looked here for help with calcs. So I am here again on a mission.

I run house automation at my location and tinker with electronics. In that system we can get info from several sources .
I am currently pulling in current conditions and forecast conditions for the next 48 hours in 6 hour requests.

I feed these into a database and now I want to compare the current conditions to those forecast 6, 12, 18 etc hours before. That is I am comparing what is now happening to what the 24 hour forecast said would happen when it was produced yesterday.

My main concern is the rain. I get probability of rain in a percent and intensity in mm/hr

I am working on combining those 2 and comparing those aginst the current conditions thus I am looking or trying to create a calculation to output a value say 0 to 100% for each of the forecasts being the 8 in the last 48 hours. Then I will say average these over a week to see which forecast was the one that was most accurate. This will be an ongoing thing and will or may change. Using these will help control the irrigation.

Has anyone done this or may suggest some ideas?

What database are you using to hold the data and forecasts?

I pull the forecasts currently from Darksky into Homeassitant (house automation). All the values the HA has are fed into InfluxDB. As part of my HA instalation I use Node-Red for automations and calcs etc. However I also use Grafana to visualise some of the data.

I am pulling the past data out of the InfluxDB using Node-Red

I have attached a screenshot of a display I have set up in Grafana just as a quick comparison