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SunnyDays

ERA5 almanac — 8 years of real data

Sydney in December

Sydney in December: 34% of days see measurable rain, 79°F average high, 33% of days historically clear (n=248, ERA5 2018–2025).

Sydney in December is historically a poor month for sun: only 33% of days clear across 8 years (n=248, avg high 79°F). Historical average, not a forecast.

What you are reading: 8-year historical averages from the ERA5 reanalysis, not a forecast. A month that is historically 90% clear can still be overcast on your specific trip. For this week’s actual forecast, see the live Sydney page. Both can be true at once: “historically strong in this month; this particular week is not.” We label which is which.

Early vs. Late December

Clear-sky percentage for Sydney in December, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early December
1st–15th		 31% n=120 79°F
Late December
16th–end		 35% n=128 79°F
Full month average 33% n=248 79°F

Sunshine & warmth in December

A second measure using actual sunshine hours (ERA5 sunshine_duration), not the daily weather code. A Lowcountry day with 12 hours of sun and a 25-minute afternoon storm is counted below as a warm, sunny day — because it was. How we define this.

Sunshine-based metrics for Sydney in December. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early December
1st–15th		 75% n=120
Late December
16th–end		 77% n=128
Full month average 76% n=248
13.0 h median sunshine per day 85% of days exceed 8 h sunshine 34% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 33%. Sunshine-based “warm & sunny”: 76%. The 43-point gap is from brief afternoon convective storms that stamp the whole day as “rain” in the WMO code but leave the bulk of the sunshine untouched.

Bottom line

Sydney is mostly overcast in December historically: only 33% of days are clear across 8 years (n=248), avg high 79°F. Most visitors this month will see more clouds than sun.

Every month in Sydney

Compare across all months with data. Numbers are historical clear-sky %.

Historical clear-sky % for Sydney, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 31% n=248 All destinations →
February 22% n=226 All destinations →
March 21% n=248 All destinations →
April 24% n=240 All destinations →
May 8% n=248 All destinations →
June 0% n=240 All destinations →
July 2% n=248 All destinations →
August 5% n=248 All destinations →
September 23% n=240 All destinations →
October 27% n=248 All destinations →
November 26% n=240 All destinations →
December ← this page 33% n=248 All destinations →

Frequently asked

Does it rain in Sydney in December?

Sometimes. Sydney sees measurable rain on 34% of days in December historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Sydney good for sun in December?

It's mixed. Sydney in December is clear on 33% of days historically (avg high 79°F, n=248 days, ERA5 2018–2025) — the outcome varies year to year.

All percentages are historical averages from the ERA5 reanalysis via Open-Meteo, 8 full years (2018–2025). “Clear” means avg high ≥ 72 °F, precipitation < 1 mm, and a non-precipitation weather code. This is history, not a forecast. The live 7-day outlook for any destination is on its own page and may differ from the long-run average. Data from Open-Meteo.