In Pamplona today, just came SJPP/ Valcarlos/ Roncesvalles / Zubiri over the last 4 days (I am a slow goer). I concur with many comments above:
1) inform yourself of current weather
2) have proper clothes and shoes for the worst weather, as it can change in 15 min
3) start the day with proper food and water. A good breakfast is important - your calorie requirements shoot up as the temp drops
4) over the last 4 days the snow at the top was firmly in place and the paths were a tough slog.
5) Still quite cold on the way down, right into Pamplona.
6) Great weather to hike, but have multiple layers with you on the trail to put on and off. I cycled through layers 1, 2, 3, 4 over the day, including down to 1 layer in clear mountain sun and back to 3 in the shadow of a ridge. Temp swung 10C in the deep shade.
Be safe, my prayers are with you all.