The High Atlas is subject to snow from November to April, and even the major Tizi n’Tichka (road to Ouarzazate) and Tizi n’Test (road to Taroudant) can be closed for periods of a day or more. These passes are seldom blocked for long and snow barriers on the roads leading up into the mountains will be down if the passes are not open to the public. If blocked, the southern regions can be reached from Marrakesh via the Tizi Maachou pass (the N8, along with the newly finished A7 toll highway towards Agadir ) followed by the N10 through Taroudant and Taliouine.
The thaw can present problems as well. When the snow melts in spring, swollen rivers are dangerous to cross. And the possibility of spring/summer flash floods must be taken seriously, as they can erupt suddenly and violently and are extremely dangerous. To keep safe, always camp on high ground while avoiding any spot where water might become a course for a torrent. This includes (even in summer) dried up and apparently terminally inactive riverbeds.