Have you compared the temperature forecasts with local official weather stations? https://community.windy.com/topic/9425/how-to-use-the-observation-vs-forecast-feature
For temperature, it seems that METEOBLUE (only available in Meteogram) matches fairly well a local Personal Weather Station (madis) close to your location :
Note that the Windy widget works only with ECMWF model and that METEOBLUE is not shown as a map neither in the weather picker (small flag), but only in Basic meteogram.
And as a conclusion the question is NOT "how accurate Windy is", because Windy does NOT make predictions, but just visualizes raw data from weather models run by major meteorological centers like ECMWF, NOAA,.... the right question would be "what is the best weather model for this location".
@Jomaba Hi, Windy does not provide archive data, so we are not able to help you. If the time range is within a few days, you can use our weather station overlay, since stations records measured data for a several days.