I, too, tried to forecast snow between SJPdP and Roncesvalles before I arrived last weekend in SJPdP -- to no avail.
When I arrived I was informed by the pilgrim office that the Napolean Route was impassable, due not to snow -- but fog -- and was directed to travel via Valcarlos, which I did.
It began to rain after I passed Valcarlos, and the rain turned to snow before I began the steep narrow ascent to Ibaneta. To my left, at the higher elevations of the Napolean Route, I could see fog and snow.
It goes without saying that I was wise to heed the direction of the pilgrim office not to attempt the Napolean Route -- despite and especially having lived in the northeast US where snow and fog are common.
Now here is what the pilgrim office could not advise -- one of many unpredictable variables along the
Camino Frances, or any hiking route through remote areas: a large tree had recently fallen and blocked the path almost completely, and this particular part of the path was not easily passable. Had I not been able to pass the fallen tree, then I could have turned back to Valcarlos. Had the path been blocked on the ascent to Ibaneta, while it was snowing, where footing was less certain, turning back would have meant a long, very long trek -- unless I managed to flag down a passing car at one of the few points where the path crosses a highway.
My point is this: the issue in crossing the Pyrenees is not only snow; it's fog, one's endurance later in the day, the steepness of an ascent or descent, whether rain has turned the path into a small brook, etc.
Be careful when deciding when and where to press on. Review the profile map the pilgrim office provides in SJPdP prior to committing to walk to the next town. Review the list of albergues open all year to know where stopping points/shelter occurs. This list also provides some limited direction as to what facilities (food, bathrooms, covered areas to change clothing/care for feet) probably will occur. (Note that published guidebooks favor April through October, not February and March -- consequently, one should be prepared to walk longer distances. more than 6-8 kilometers between facilities).
Finally, as to snow between SJPdP and Roncesvalles, I am told half a meter of snow fell earlier this week after I crossed Ibaneta. As Falcon and others advise: the weather is unpredictable, even within a single day.
Be careful.
