Herman. Just referring to the fact I have jet to come across a forecaster in any country that can forecast the weather accurately so why should I believe them fully when forecasting ash profiles.
it's way above the weather and once identified the imaging can be tracked with the high altitude winds and the forecasting that counts is not measured in days like you care about the weather.
As for the accuracy, it isn't a case of possible showers, you simply don't fly into the visible cloud