Snowdonia National Park in January

May through September offers your best shot at decent weather, but 'decent' in Snowdonia means different things. May brings longer days and fewer crowds, but expect mud and unpredictable conditions. The Welsh saying goes: 'If you can see Snowdon, it's about to rain. If you can't see Snowdon, it's already raining.' June and July deliver peak conditions - longest days, warmest temperatures, best chance of clear summits. But everyone knows this. Snowdon's main paths turn into conga lines. Start early or pick weekdays. August stays busy but weather remains reliable. September is the sweet spot - crowds thin out, weather often holds, autumn colors start showing in the valleys. Winter transforms the park into serious mountaineering territory. Snow and ice require crampons and ice axes. Daylight shrinks to 8 hours. But clear winter days offer the most spectacular views of the year. Here's the thing about Snowdonia weather: it changes fast and varies dramatically by elevation. Valley towns like Betws-y-Coed might be sunny while Snowdon's summit sits in cloud. Check mountain weather forecasts, not general area predictions. MWIS (Mountain Weather Information Service) gives detailed mountain-specific forecasts.