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.
Sports-science studies of marathon finishing times consistently identify 7–13°C as the sweet spot — cold enough to dissipate body heat, warm enough that muscles stay responsive. Performance drops about 1–2% per °C above 15°C. Below 0°C the pace penalty returns as muscles tighten and air becomes harder to warm in the lungs. A 0–100 score from a pure function with six inputs: temperature (the strongest signal), humidity, wind, rain in the next hour, UV index and air quality (AQI). The score starts at 70 — a good run is the default — and weather subtracts more than it adds. Heat + humidity stacks fastest, and AQI above 200 can cap the score under 30 alone. Running heat dissipation depends almost entirely on sweat evaporation. Above 70% relative humidity that mechanism fails — sweat sits on the skin instead of cooling you. At 22°C with 80% humidity, your body strains harder than 28°C with 30% humidity. The Running Score weighs humidity heavily once temperature is above 15°C. A combined index that adjusts air temperature for humidity (heat index, warm side) and wind chill (cold side). The Decision Card shows feels-like below the archetype label. Use it — not the dry temperature — to decide pace, kit and route. If the forecast feels-like at 09:00 is above 22°C, move the run to 05:30–07:00 — air temperatures rise 3–6°C between dawn and 10:00. Dawn also delivers the lowest UV of the day, lowest typical wind, and lowest urban AQI. A rough rule from marathon physiology research: subtract about 1% from your goal pace for every 5°C above 15°C feels-like (over the whole race window). At 25°C feels-like, expect 2–4% slower finishing time — even with perfect pacing. The Verdict Grid above gives a live read. Feels-like temperature above 22°C is statistically the #1 destroyer of planned sessions, followed by AQI above 100 and sustained wind above 25 km/h. Rain is rarely the limiting factor below 4 mm/h; chafing kit and footing are. Yes — and you should, when conditions cross any of the "Skip" verdicts above. Treadmill is a faster, safer choice than a DNF on a heat-stressed long run. Set incline to 1% to mimic outdoor effort. Pre-cool with ice slurry or cold shower, dawn timing only, halve the planned distance, carry 500 ml + electrolyte tabs, route past water fountains, white visor + sunglasses, light-coloured technical kit. Cap effort at conversational — never speedwork above 25°C feels-like. AQI above 150 is unhealthy for any aerobic activity — particulate dose = AQI × minutes. Treadmill is the only safe choice. Even at AQI 100, drop intervals and shorten the long run. Asthmatic runners should mask up at AQI 50+. Under 60 min: water is enough. Above 60 min in heat: sodium matters — water alone causes hyponatremia. Aim for 300–700 mg sodium per litre of fluid for runs over 90 min. No. Compression below the knee provides marginal benefit at the cost of trapping heat. Above 22°C feels-like, fewer layers is the better play. Most healthy adults can run safely down to about -15°C if dressed properly. Below -20°C feels-like, exposed skin frostbites in 15–30 min and inhaled air can trigger asthma. Treadmill below -20°C wind-chill, full-balaclava run between -10 and -20°C. Long thermal tights, technical T + thin wind-shell, buff over ears, lightweight gloves. The rule: dress for 8–10°C warmer than the actual temperature — the first kilometre is cold, kilometres 2–10 you'll be glad you didn't over-layer. When wind is above 25 km/h and temperature below 8°C — yes, every time. A wind-shell adds about 5°C of perceived warmth at almost zero weight or breathability penalty. For sheer iconic status: Central Park 6-mile loop (NYC), Bondi-to-Coogee (Sydney), Hyde Park & Serpentine (London). For training reliability: Sognsvann forest loop (Oslo), Flagstaff Lake Mary (Arizona altitude base), Imperial Palace loop (Tokyo, 20,000 runners daily). Use the Plan My Run wizard above to match a route to your goal. Any precipitation above 1 mm/h makes technical trails dangerous — wet roots and rocks send most trail injuries. Switch to paved or fire-road tread in rain, mud or sub-zero ground (where mud freezes into ankle-traps).
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 Running Decision Guide's own coordinates and time zone. Full details on the methodology page.