How the Sunset Forecast Works

Skying is a small sunset-planning tool built by Gaurav Sharma. It combines a weather forecast with a transparent scoring rule to help you decide when to look at the sky. The score has not been calibrated against a dataset of observed sunset photographs.

What goes into the score?

Skying reads hourly cloud cover at low, middle and high levels, visibility, precipitation probability and relative humidity from Open-Meteo. It averages available observations within 90 minutes of sunset, giving more weight to times closer to sunset.

• 34% upper-cloud suitability: a blend of 72% high and 28% middle cloud, with the highest suitability between 30% and 70% cover.
• 30% horizon conditions: a penalty for low cloud and very heavy total cloud. This is a weather-based estimate, not a map of buildings or hills.
• 14% visibility: clearer air receives a higher score.
• 12% rain conditions: lower precipitation probability receives a higher score.
• 10% humidity: lower near-surface relative humidity receives a higher score in this heuristic.

Very heavy total cloud or an almost cloudless sky receives a further 12-point reduction. The result is rounded and limited to 0–100. Missing required weather data produces an unavailable score, not an invented value.

How to read the number

90–100 is Exceptional, 78–89 Excellent, 63–77 Good, 45–62 Average and below 45 Poor. These are Skying’s descriptive categories. A score of 80 does not mean an 80% chance of a colourful sunset.

Dates, daylight and freshness

Sunset times come from Open-Meteo. Golden hour is calculated using SunCalc, from +6° to −4° solar altitude; blue hour runs from −4° to −6°. Definitions vary between photographers. These estimates do not model your exact horizon, refraction or terrain.

Each page shows its location’s timezone and the time Skying retrieved the weather data. This retrieval time is not the weather model’s issuance time. Forecasts can be reused for 30 minutes. If a refresh fails, a saved forecast may be shown for up to six hours, only on the same local day, with a clear warning. Cached data is best-effort and may not be available everywhere.

What the forecast cannot promise

Skying does not directly model aerosol colour, smoke, the view toward the distant horizon or the beauty of a photograph. Longer-range cloud predictions may change. Use the seven-day outlook for planning, check again near the time, and observe actual conditions. At high latitudes, a sunset or complete light interval may not occur on a particular day.

Location search uses Photon and OpenStreetMap contributors. Curated cities use fixed city-centre coordinates; a precise-location forecast uses the coordinates you request. Inspect the source and scoring rules on GitHub.