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SunnyDays

ERA5 almanac — 8 years of real data

Boston in August

Boston in August: 39% of days see measurable rain, 82°F average high, 41% of days historically clear (n=248, ERA5 2018–2025).

Boston in August is a mixed month for sun: 41% of days historically clear (n=248, avg high 82°F). The outcome varies year to year — check the early/late split below. 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 Boston 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 August

Clear-sky percentage for Boston in August, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early August
1st–15th		 41% n=120 82°F
Late August
16th–end		 41% n=128 82°F
Full month average 41% n=248 82°F

Sunshine & warmth in August

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 Boston in August. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early August
1st–15th		 92% n=120
Late August
16th–end		 83% n=128
Full month average 87% n=248
12.5 h median sunshine per day 82% of days exceed 8 h sunshine 39% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 41%. Sunshine-based “warm & sunny”: 87%. The 46-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

Boston in August is genuinely mixed: 41% of days historically clear (n=248), avg high 82°F — more cloudy than clear. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Boston

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

Historical clear-sky % for Boston, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 0% n=248 All destinations →
April 2% n=240 All destinations →
May 17% n=248 All destinations →
June 33% n=240 All destinations →
July 37% n=248 All destinations →
August ← this page 41% n=248 All destinations →
September 31% n=240 All destinations →
October 12% n=248 All destinations →
November 2% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Boston in August?

Sometimes. Boston sees measurable rain on 39% of days in August historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Boston good for sun in August?

It's mixed. Boston in August is clear on 41% of days historically (avg high 82°F, n=248 days, ERA5 2018–2025) — the outcome varies year to year.

How Boston compares in August

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Boston this month — same passport tier, similar flight distance, both sides from the same 8-year ERA5 record.

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.