Portugal weather by month

In Lisbon, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.

The clearer part of the year begins around May 14 and lasts for 4.8 months, ending around October 6. The clearest month is July, when the sky is clear, mostly clear, or partly cloudy 93% of the time on average.

The cloudier part of the year begins around October 7 and lasts for 7.2 months, ending around May 13. The cloudiest month is December, when it is overcast or mostly cloudy 52% of the time.

This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.

Across the year, average wind speed in Lisbon is typically light breeze, near 17 km/h, and varies little with the seasons.

The windier part of the year lasts 5.0 months, from around Mar 27 to Aug 26. The windiest month is July, averaging about 20 km/h (light breeze).

The calmer part of the year runs from around Aug 27 to Feb 23, with October the calmest month at about 16 km/h.

Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.

Lisbon receives about 4.8 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 2.0 and 7.6 kWh/m².

The brighter stretch of the year lasts 6.1 months, from around Mar 21 to Sep 23. The brightest month is July, averaging about 7.6 kWh/m² (intense).

The dimmest month is December, down near 2.0 kWh/m² — roughly 73% less than the July peak.