Sadly there is no reliable way to predict weather two weeks or more in advance. The longer the forecast the less confidence you can place in it. It may not be the answer you would like but I think the only sensible advice is "hope for the best but prepare for the worst". You can find historical weather data online for places along your route at weatherspark.com but an average is no real guide to actual day-by-day weather.
Hola @Dianes954 , unfortunately meteorology is still an inexact science, it’s now reasonably accurate at 7 days, but not 14-20. So what to do? Come prepared for cold & rain, if it does not eventuate then great. I did not see your starting point, but if it’s St Jean then based on the most recent snowfalls it’s quite likely that the Napoleon track, via Orisson may still be a less than viable option. If this is the case Valcarlos is this a great way to start your Camino. If starting in. Spain, not a problem, just take each day as it comes. Welcome
You are going to walk ACROSS a country , you will get every type of weather .
You will also enjoy talking to your fellow pilgrims when in the mud because you ain't going too quick.
Just like life , enjoy the unexpected .
You'll soon know what the weather will be like . Assuming that you start in SJPP, here's the "5 days meteogram" for the top of the Route Napoleon. Although we are quite close to the date now, the predictability is still at the level of medium to low for these days. Looks like fairly cold, a bit of rain sometimes, very windy at times and days with not much to see as the cloud cover is low. Buen camino!