Altitude and weather conditions
The Via Francigena is practicable for most of the year, although not necessarily recommended. However, if you are walking all the way from Canterbury to Rome in one go or are starting from the Grand St Bernard Pass you will need to plan your journey to take into account the altitude and weather conditions at 2473m (8114ft) above sea level.
The Grand St Bernard Pass in winter is accessible only on skis or snow shoes, and the only safe alternative for walkers when the pass is snowbound is to take the bus under the tunnel from Bourg-Saint-Pierre. The pass is normally free from snow from late May to late September, although snowfalls can occur at night even during July and August (and snow remains during the day).
If you are starting in Aosta, or further on, in the winter, early spring or autumn, you may be able to avoid the heat in Italy for a substantial part of your journey, although the advantages of cooler weather will be offset by shorter hours of daylight.