About & Data

ClimateWhen helps travellers decide when to go. For each destination we publish month-by-month averages of temperature, rainfall, humidity, cloud cover and daylight, and a simple comfort rating.

Where the data comes from

Climate averages come from NASA POWER (Prediction Of Worldwide Energy Resources), using 20 years of daily data (2005–2024), averaged by calendar month. NASA POWER combines satellite observations and the MERRA-2 reanalysis on a grid of roughly 50 km. Because a grid cell can sit higher or lower than the city itself, we adjust temperatures for the city's real elevation using a standard lapse rate of 6.5°C per 1,000 m. City locations come from GeoNames.

How the comfort rating works

Each month gets a score from 0 to 10. A month scores highest with daytime highs between 22°C and 28°C, little rain, moderate humidity and clear skies. We take points off for heat, cold, heavy rain, muggy humidity and persistent cloud. Ratings are Excellent (8+), Good (6.5+), Fair (4.5+) and Poor.

Limitations

These are long-term averages, not forecasts. Weather in a particular year can be very different, and gridded data can smooth out local effects such as sea breezes or mountain valleys. Always check a forecast before you travel.