United Kingdom weather by month

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

The clearer part of the year begins around June 25 and lasts for 2.7 months, ending around September 15. The clearest month is August, when the sky is clear, mostly clear, or partly cloudy 35% of the time on average.

The cloudier part of the year begins around December 17 and lasts for 3.7 months, ending around April 8. The cloudiest month is March, when it is overcast or mostly cloudy 72% 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 London is typically light breeze, near 15 km/h, and varies little with the seasons.

The windier part of the year lasts 5.6 months, from around Oct 13 to Apr 1. The windiest month is January, averaging about 17 km/h (light breeze).

The calmer part of the year runs from around Apr 2 to Oct 12, with July the calmest month at about 13 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.

London receives about 2.9 kWh/m² a day of solar energy on average — moderate — with a clear seasonal swing between 0.6 and 5.3 kWh/m².

The brighter stretch of the year lasts 5.9 months, from around Mar 22 to Sep 17. The brightest month is June, averaging about 5.2 kWh/m² (bright).

The dimmest month is December, down near 0.7 kWh/m² — roughly 87% less than the June peak.