i find a lot of weather info from apps to be quite inaccurate compared to jma, but jma will only give a detailed forecast up to 2 days in advance, and those forecasts out into the weak have a reliability rating from A-C...
jma's forecast for takayama is snow for thurs, cloudy for fri (40% rain), cloudy sat (40% reliability C), sun snow (50% reliability C), mon-wed snow (70% reliability B/A/B).
jma is known to change their forecast beyond the 2 days ahead very often, so it is always prudent to check regularly
weather prediction is an inexact science... a lot is based on computer modelling and those models are not very precise. it is impossible to narrow it down to a small village.'
if you die die must have a prediction for shirakawago, however inaccurate it may be, tenki.jp has the prediction
http://www.tenki.jp/forecast/5/24/5220/21604.html