High mountain passes close each winter and reopen in late spring, on dates that vary considerably from year to year. The decisions are operational rather than purely meteorological.
Closure is a resource decision
Keeping a high pass open through winter requires continuous clearance, avalanche control and staff stationed nearby, at a cost proportional to how often it snows.
Where a tunnel or a lower route provides an alternative, the authority compares that cost against the benefit of keeping a seasonal road available.
Passes serving significant year-round traffic are kept open at considerable expense, while scenic passes with a viable alternative are closed and left.
Avalanche risk governs the timing
Roads crossing avalanche paths cannot be reopened until the slopes above have stabilised or been made safe, which depends on snowpack structure rather than on the calendar.
Control work involves triggering slides deliberately under managed conditions, and it requires suitable weather and visibility to be carried out.
A warm spell can increase risk rather than reduce it, since water moving through the snowpack weakens the bonds holding it to the slope.
Clearing is slower than it appears
Snow accumulated over months compacts and freezes, and drifts on lee slopes can be many metres deep where the road is entirely buried.
Machinery works from both ends toward the summit, and progress is measured in a modest number of metres per hour through the deepest sections.
The road surface underneath must then be assessed and repaired, since freeze-thaw damage and rockfall are routine consequences of a winter under snow.
Reopening is staged rather than immediate
Passes frequently open first to cyclists and pedestrians, or for limited daytime hours, before full unrestricted access is granted.
Weather can force a reopened pass to close again, and late-season snowfall in the mountains is common well into the spring.
Published opening dates are therefore forecasts, and the authoritative source is the road authority's live status rather than any seasonal listing.
What this means for planning a route
Itineraries built around a specific pass need an alternative, because a closure discovered at the foot of the climb can add several hours.
Navigation software does not always reflect seasonal closures accurately, particularly on minor roads, which is why local status pages matter.
Fuel and food availability follow the same season, so a pass that has just opened may have services that have not, which is worth planning around.