SunWhen is a free web application that predicts when the sun will be visible at your location. Unlike traditional weather apps that show general conditions, SunWhen specifically answers the question: "When will I see the sun?"
We combine weather forecast data with astronomical calculations to identify clear sky periods during daylight hours.
Simply open SunWhen in your web browser. The app will:
That's it! No account needed, no app to download.
Sun visibility depends entirely on your specific location. Cloud cover, sunrise/sunset times, and weather patterns all vary by location—sometimes significantly even within the same city.
We use your coordinates to fetch accurate local weather data. Your location is only used for this purpose and is never stored on our servers.
No problem! If you deny location access or your browser doesn't support geolocation, you can manually enter latitude and longitude coordinates.
To find coordinates for any location, you can use Google Maps: right-click on a location and the coordinates will appear.
SunWhen analyzes hourly weather forecasts from Open-Meteo, focusing on cloud cover data. For each hour, we check:
Hours that meet both criteria are marked as "clear" and grouped into clear periods.
Accuracy depends on how far ahead you're looking:
Weather is inherently unpredictable, so we recommend checking back regularly for updated forecasts.
The cloud cover threshold lets you customize what "clear" means to you. It's a percentage from 10% to 90%.
The default is 50%, which works well for most people. Adjust it based on your activity—photographers might want lower thresholds, while someone just wanting to go for a walk might be fine with higher values.
The chart shows cloud cover for each hour:
The height of each bar represents the cloud cover percentage. The dashed line shows your current threshold setting.
This shows the expected duration of the clear period. It's calculated by counting consecutive hours where cloud cover is predicted to stay below your threshold during daylight.
Longer clear periods are generally more reliable predictions than short ones.
We use the Open-Meteo API, which aggregates data from national weather services worldwide including:
Open-Meteo provides high-quality, open-source weather data that's updated hourly.
Yes! SunWhen works for any location on Earth. Weather data is available globally through the Open-Meteo API, and sunrise/sunset calculations work for all coordinates.
However, forecast accuracy may vary by region depending on the density of weather stations and quality of local meteorological data.
No, SunWhen requires an internet connection to fetch current weather data. Weather forecasts change frequently, so we always retrieve the latest data when you open the app.
SunWhen is a web application that works in any modern browser, including mobile browsers. You can add it to your home screen for quick access:
This gives you app-like access without needing to download anything.
No. Your location is only used in real-time to fetch weather data. We don't store your coordinates on our servers, and we don't track your location history.
Your threshold preference is saved locally in your browser (localStorage) for convenience.
We use minimal cookies for:
We don't use cookies to track your personal information or location.
Yes, SunWhen is completely free to use. We use the Open-Meteo API which provides free weather data, and the site is supported by advertising.
There are no premium features, subscriptions, or hidden costs.
SunWhen was created by weather enthusiasts who wanted a simple answer to a simple question: "When will the sun come out?"
Learn more on our About page.
We'd love to hear from you! Whether you have suggestions, found a bug, or just want to say hello, you can reach us at:
Email: hello@sunwhen.com
SunWhen is intended for personal use. If you're interested in commercial applications or API access, please contact us to discuss options.