About SunScope
The True Temperature — what the weather actually feels like on your body.
What is SunScope?
SunScope is a free outdoor thermal comfort forecast that goes beyond standard air temperature. Most weather apps tell you it's 12 °C and leave you to guess whether that means t-shirt weather or a heavy coat. SunScope combines air temperature, humidity, wind speed, and solar radiation into a single felt temperature — so you know what to actually expect when you step outside.
It uses the Universal Thermal Climate Index (UTCI), a peer-reviewed biometeorological standard developed by Bröde et al. (2012) and used globally in heat-health warning systems and urban planning. Forecast data is sourced in real time from Open-Meteo, a free and open-source weather API drawing on ECMWF and national met services. SunScope is available for any location worldwide.
What is the SunScope soak-factor?
Standard UTCI does not account for precipitation — it tells you how cold the wind and sun make you feel, but not the extra chill of rain soaking your clothing or snow settling on your skin. The SunScope soak-factor fills that gap with an original penalty formula.
Light drizzle (under 1 mm/hr) reduces the felt temperature by roughly 1–2 °C. Heavy rain combined with strong wind can push it down by 7–8 °C. Snowfall carries an additional penalty on top of any rain adjustment. The result is shown in the UTCI+P column — a more honest, real-world comfort score for anyone heading outdoors.
Reading the stress bands
SunScope maps every UTCI+P value to a thermal stress band so you can read conditions at a glance:
| UTCI range | Band | What it means outdoors |
|---|---|---|
| Below −27 °C | Polar | Survivable only with expedition-grade kit; do not go outside unprepared |
| −27 to −13 °C | Arctic | Very strong cold stress; full winter protection needed |
| −13 to 0 °C | Freezing | Strong cold stress; warm layers essential |
| 0 to 9 °C | Cold | Moderate cold stress; coat and gloves advised |
| 9 to 18 °C | Chilled | Slight cold stress; comfortable with a light jacket |
| 18 to 26 °C | Comfortable | No thermal stress; ideal outdoor conditions |
| 26 to 32 °C | Mod heat | Moderate heat stress; stay hydrated |
| 32 to 38 °C | Strong heat | Strong heat stress; limit strenuous activity |
| 38 to 46 °C | V. strong heat | Very strong heat stress; seek shade and cool fluids |
| Above 46 °C | Extreme heat | Extreme heat stress; dangerous for outdoor exposure |
Frequently asked questions
Why does SunScope sometimes show a much higher temperature than my regular weather app?
On clear, sunny days direct solar radiation heats your skin significantly — sometimes adding 10 °C or more to what the air temperature alone would suggest. SunScope calculates Mean Radiant Temperature from shortwave radiation data, capturing this effect. Standard weather apps ignore it entirely.
Why does SunScope sometimes show a lower temperature than my regular weather app?
Wind chill and precipitation both reduce felt temperature. If it's raining or blustery, the UTCI+P value will be noticeably lower than the thermometer reading — which is exactly what your body experiences.
How far ahead does the forecast go?
SunScope currently shows a 72-hour hourly forecast. Data refreshes automatically from Open-Meteo each time you load the page.
Is SunScope free?
SunScope beta is currently free to use for any location worldwide. As the product develops, some features may move to a paid tier — but core forecasting will always be accessible.
What data sources does SunScope use?
Forecast data comes from Open-Meteo, which aggregates ECMWF, GFS, and national meteorological service models. The UTCI calculation follows the Bröde et al. 2012 polynomial. Geolocation search uses the Open-Meteo geocoding API.
Get in touch
SunScope is an independent project. If you have feedback, spotted a bug, or are interested in using SunScope data for your business or website, feel free to reach out via hello@sunscope.net.