It is the responsibility of walkers to contact the leader if they feel there is a doubt that the walk will take place. Typically, this would be in the event of very bad weather conditions. For example, heavy rain should not prevent a rendezvous, whereas ice, snow, flood or, the other extreme, scorching heat, would do so. Flooding might prevent access both to the start point and the route! Leaders are not expected to take risks getting to the start point in such weather.
In the event of adverse weather conditions the walk leader has the authority to adapt the walk route and distance as required. The leader will advise walkers at the start of the walk.