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SunnyDays

ERA5 almanac — 8 years of real data

Charleston in December

Charleston in December is historically a poor month for sun: only 2% of days clear across 8 years (n=248, avg high 61°F). October is the clearest month for Charleston historically. 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 Charleston 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 Charleston 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		 1% n=120 61°F
Late December
16th–end		 3% n=128 61°F
Full month average 2% n=248 61°F

Bottom line

Charleston is historically almost never clear in December: only 2% of days meet the clear bar across 8 years (n=248). Come back in October if you want clear skies here. Plan entirely around indoor or overcast-friendly activities.

→ See all destinations in October — historically the best month for sun in Charleston.

Every month in Charleston

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

Historical clear-sky % for Charleston, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 1% n=248 All destinations →
February 5% n=226 All destinations →
March 12% n=248 All destinations →
April 38% n=240 All destinations →
May 37% n=248 All destinations →
June 22% n=240 All destinations →
July 12% n=248 All destinations →
August 12% n=248 All destinations →
September 32% n=240 All destinations →
October 45% n=248 All destinations →
November 12% n=240 All destinations →
December ← this page 2% n=248 All destinations →

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.