Isle of Man weather by month

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

The clearer part of the year begins around March 31 and lasts for 5.5 months, ending around September 13. The clearest month is May, when the sky is clear, mostly clear, or partly cloudy 45% of the time on average.

The cloudier part of the year begins around September 14 and lasts for 6.5 months, ending around March 30. The cloudiest month is December, when it is overcast or mostly cloudy 69% 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 Douglas is typically windy, near 29 km/h, and varies a lot with the seasons.

The windier part of the year lasts 5.8 months, from around Sep 28 to Mar 23. The windiest month is January, averaging about 35 km/h (windy).

The calmer part of the year runs from around Mar 24 to Sep 27, with July the calmest month at about 23 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.

Douglas receives about 3.1 kWh/m² a day of solar energy on average — moderate — with a clear seasonal swing between 0.5 and 5.8 kWh/m².

The brighter stretch of the year lasts 5.8 months, from around Mar 24 to Sep 16. The brightest month is June, averaging about 5.8 kWh/m² (bright).

The dimmest month is December, down near 0.5 kWh/m² — roughly 91% less than the June peak.