South Africa weather by month

In Johannesburg, 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 April 18 and lasts for 5.7 months, ending around October 9. 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 10 and lasts for 6.2 months, ending around April 17. The cloudiest month is December, when it is overcast or mostly cloudy 45% 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 Johannesburg is typically calm, near 10 km/h, and varies little with the seasons.

The windier part of the year lasts 5.0 months, from around Jul 25 to Dec 24. The windiest month is September, averaging about 12 km/h (light breeze).

The calmer part of the year runs from around Dec 25 to Jul 24, with March the calmest month at about 9 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.

Johannesburg receives about 5.6 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 3.9 and 6.9 kWh/m².

The brighter stretch of the year lasts 6.4 months, from around Sep 1 to Mar 14. The brightest month is December, averaging about 6.8 kWh/m² (intense).

The dimmest month is June, down near 3.9 kWh/m² — roughly 42% less than the December peak.