Conditions on this page are recalculated from the latest forecast every time it is opened, for the current date in the location's own time zone.
Lightning above treeline is the #1 mountain killer. No summit is worth it. 10–20°C (50–68°F) at the trailhead is ideal. Your body generates 300–600 W of heat on moderate climbs vs ~80 W at rest, so it dissipates exercise heat efficiently in this range without sweating heavily or needing bulk insulation. Above 25°C heat stress builds, below 5°C hypothermia becomes the dominant risk if you stop moving. Below 15 km/h is ideal. 15–30 km/h is fine in forest but blustery on ridges. 30–50 km/h is genuinely strong — avoid exposed ridgelines. Above 50 km/h sustained is dangerous on summits and exposed scrambling terrain; stay below treeline. 30% probability that measurable rain will occur somewhere in the forecast area during the period — not 30% of your hike. Look at expected rainfall amount, hourly timing, and the radar trend rather than the headline percentage. A 30% afternoon storm risk on an exposed alpine route deserves more caution than 30% morning drizzle in forest. Roughly −6.5°C per 1,000 m gained (the environmental lapse rate) on a clear, calm day. Add wind chill on exposed ridges and a 22°C valley start can read 7°C with significant felt-temp cooling on a 2,500 m summit. The Trail Weather Matrix above models exactly this. In summer alpine terrain, convective storms typically fire 13:00–17:00 as the ground heats. The standard mitigation is a pre-dawn start (4–6 AM trailhead) so you summit before 11:00 and are below treeline before the cells build. The UCI uses the same logic for bike races. Above 30°C heat stress builds rapidly with exertion. Above 35°C heat stroke risk is real for fit hikers, especially on exposed climbs. The standard mitigation is a pre-dawn start, finishing by midday. Above 40°C, postpone — no scenic vista is worth heatstroke. Any storm cell within 8 km, any thunder you can hear, any rapidly building cumulus before noon, or a forecast convective storm risk above 30% in alpine terrain. Get below treeline immediately, off summits and ridges, away from solo trees and metal objects. Lightning is the #1 mountain killer of summer hikers in the US Rockies. Air temperature 0–10°C combined with rain and wind — not deep cold. A wet hiker in 5°C with 30 km/h wind loses core temperature fast, especially after they stop moving (rest break, injury, navigation pause). Hardshell jacket + fleece base layer prevents almost all of these cases. Storm cells building before your summit window closes; sustained wind above your gear's comfort zone; visibility dropping below 5 km on unmarked terrain; a member of your party showing symptoms of altitude sickness, hypothermia or heat exhaustion. Turning back at the right time is the single most important mountain skill. Depends on the trail. Alps and Rockies: late June to early September for snow-free passes. Patagonia: November to March (austral summer). High Andes (Inca Trail): May to September (dry season). Mediterranean trails (Cinque Terre): April to October but avoid July–August heat at midday. The Best Hiking Trails section above lists optimal months per trail. Half Dome (Yosemite), Inca Trail, Angels Landing, Kilimanjaro, Mount Fuji, Cinque Terre Sentiero Azzurro and Torres del Paine W Trek all require permits — most book out months ahead. The Plan My Hike tool above flags permit-required trails when you toggle "permits OK". On most European trails yes (Trolltunga, Preikestolen, Snowdon, Camino Francés, Cinque Terre — though with leash rules). On US national park summit trails generally no (Half Dome, Bright Angel, Angels Landing). The CompareTrails tool above shows dog-friendly status per trail. Navigation (map + compass or GPS), sun protection (sunscreen + hat + sunglasses), insulation (extra layers), illumination (headlamp + spare batteries), first-aid supplies, fire-starting kit, repair kit + tools, nutrition (extra day of food), hydration (extra water), emergency shelter. The Live Packing List above adds weather-conditional items on top of these. Minimum 0.5 L per hour of moderate hiking in mild conditions. 1 L per hour in heat (above 25°C) or above 2,500 m altitude. Always carry a filter or purification tablets so you can refill from streams. Run-out is a leading cause of mountain rescues — never trust a dry-looking spring. Fine in forest, blustery on exposed ridges. Secure hats and loose gear.
Scores are capped by dealbreakers — heavy rain, dangerous wind, thick fog or hazardous UV pull a day down no matter how pleasant the rest of the numbers look. Forecast data is Open-Meteo; solar and lunar values are computed for Good Hiking Day's own coordinates and time zone. Full details on the methodology page.