Conditions on this page are calculated for . The live tool above re-runs the same model against the latest forecast for today's date.
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).
Weather decisions in Running Decision Guide are rarely about whether it's "nice" — they're about matching what you want to do with the conditions that actually show up. A perfectly sunny day at 34 °C can be a bad day for hiking, a mild overcast morning can be ideal for portrait photography, and a low-cloud evening can be a spectacular night for full-moon shots. Snap Weather is built to answer decision questions like these directly, rather than making you interpret raw forecast numbers on your own.
This page pulls the current Open-Meteo forecast for Running Decision Guide and reframes it around one specific decision. If the conditions clearly support the plan, we say so; if they don't, we say that too and — where possible — suggest the next date in the outlook window that does. Recommendations respect timezone, sunrise/sunset, forecast uncertainty and dealbreaker thresholds (heavy rain, dangerous wind, thick fog, hazardous UV), so a warning stays a warning even when everything else looks pleasant.
The decision score you see on this page is a weighted composite of the factors most important to the question in the page title. Weights differ by decision type, and every factor has a "dealbreaker" cap: if a single factor is dangerous or ruins the plan, the total score is pulled down regardless of the other factors.
Because dealbreaker caps apply, a "poor" score is not simply a low weather score — it means at least one factor makes the plan meaningfully worse or unsafe. That's the difference between a decision engine and a raw weather feed.
The table below summarises the typical weather pattern travellers can expect across the year in Running Decision Guide. It's a long-term climatological reference — the live tool at the top of this page overlays the current 7-to-14-day forecast on top of these baselines, so any anomalies (a cold spring, a wet summer, an unusual heatwave) show up immediately.
| Month | Season | Typical pattern | Traveller notes |
|---|---|---|---|
| January | Mid-winter (N) / peak-summer (S) | Coldest and shortest days in the northern hemisphere; warmest in the southern hemisphere. | Best value in most Europe/N-America; peak season in Australia/S-America/S-Africa. |
| February | Late-winter (N) / late-summer (S) | Cold and often driest month in the north; warm and stable in the south. | Ski season is at its most reliable in the northern hemisphere. |
| March | Early-spring (N) / early-autumn (S) | Rapidly lengthening days in the north; cooling but still pleasant in the south. | Shoulder pricing across most tourist cities. |
| April | Mid-spring (N) / mid-autumn (S) | Warming with unstable showers in the north; mild and dry in the south. | Cherry blossom windows across Europe, N America and East Asia. |
| May | Late-spring (N) / late-autumn (S) | Warm days, cool evenings in the north; first frosts possible in the south. | Widely considered the best value month for European city trips. |
| June | Early-summer (N) / early-winter (S) | Long days, warming quickly in the north; short days and cold in the south. | Solstice window; peak golden hour length in far-north cities. |
| July | Peak-summer (N) / mid-winter (S) | Warmest month across most of the northern hemisphere; ski season in the south. | Heatwave risk in southern Europe and inland US. |
| August | Late-summer (N) / late-winter (S) | Warm and often humid in the north; last month of ski season in the south. | Monsoon peak in South and Southeast Asia. |
| September | Early-autumn (N) / early-spring (S) | Cooling, drier and more stable in the north; warming in the south. | Widely rated the best month for Mediterranean travel. |
| October | Mid-autumn (N) / mid-spring (S) | Foliage peak in temperate north; blossom season starting in the south. | Photography prime time; long golden-hour windows. |
| November | Late-autumn (N) / late-spring (S) | First cold spells in the north; warming rapidly in the south. | Off-season pricing across most Europe/N America. |
| December | Early-winter (N) / early-summer (S) | Shortest days and often the wettest month in maritime climates; long warm days in the south. | Solstice window; ski openings across the northern hemisphere. |
Season labels use the northern-hemisphere calendar for consistency. If Running Decision Guide sits south of the equator, the live tool at the top of the page inverts these automatically using the location's coordinates.
Snap Weather pulls forecast data every hour from Open-Meteo and combines it with high-precision solar and lunar calculations done in Running Decision Guide's local timezone. We translate raw numbers into a direct answer to the question in the page title. Every score is capped so a single dealbreaker — heavy rain, dangerous wind, thick fog, hazardous UV — cannot be hidden by otherwise pleasant averages, and every recommendation includes a plain-English explanation of why we picked what we picked.
Uncertainty is stated rather than hidden. Every day carries a confidence band that falls with forecast lead time and with how variable the forecast itself is: days one to three are normally safe to plan around, days four to six describe a direction of travel, and anything beyond a week should shape intent rather than a booking. This confidence figure is a transparent, documented function of lead time and forecast variability — it is not a measurement of ensemble member spread, and we do not present it as one.
The methodology is documented in full on our methodology page, and the scoring code for each decision type — travel days, photography, weddings, activities, ski, running, cycling — is written in a shared, activity-aware library so recommendations stay consistent across every page on the site.
All times on this page render in the local timezone of Running Decision Guide, not your device timezone, so a sunrise time you read from London still means "sunrise as seen from Running Decision Guide". Weather data comes from Open-Meteo's hourly forecast API, which serves a blend of leading global models (ECMWF, GFS, ICON) at roughly 11 km resolution. Astronomical data — sunrise, sunset, twilight, moon phase, illumination and moon altitude — comes from the Sunrise-Sunset API with Open-Meteo as a resilient fallback, and every calculation is done in the target location's timezone rather than the browser's, so daylight-saving transitions, high-latitude twilight and equatorial no-twilight days all render correctly.
We publish a last-updated timestamp on the live page so you can see exactly how fresh the numbers are, and we display forecast confidence next to each day so you know when it's safe to lock in plans and when to check back after the next model run. The interactive tool at the top of this page is fully client-side — no accounts, no paywall, no email required — and it works on mobile and desktop equally well.
Weather data refreshes hourly from Open-Meteo. Solar and lunar timings are re-computed on every page load, so a page you refresh at midday and again at 6 pm can show meaningfully different scores if a model run has arrived in between.
Yes. Every forecast, decision score, month-by-month guide and photography timing on Snap Weather is free, no account required and no data captured beyond anonymous analytics. If it saves you a trip or a shoot, telling a friend is the only "payment" we ask for.
We use Open-Meteo's forecast API, which serves a blend of leading global models (ECMWF, GFS, ICON) at roughly 11 km resolution. This is the same model family used by many professional planning tools, exposed here in a decision-friendly way.
Yes — all sunrise, sunset, twilight and moon times are calculated in the destination's local timezone, so daylight-saving transitions are handled automatically. You should never need to add or subtract an hour manually.
Trust decays with time. Days 1–3 are typically very reliable, days 4–7 are directionally reliable (good/bad but not exact), and days 8–14 give you a broad sense of the pattern. That's why we surface confidence alongside every score.
Snap Weather is a weather decision engine. You can search any of the 11M+ locations in the Open-Meteo geocoding database, and we publish in-depth pages for 350+ curated destinations. If you're on the live site, the interactive forecast for Running Decision Guide loads automatically — no reload required.