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SunnyDays

ERA5 almanac — 8 years of real data

Seattle in August

Seattle in August: 15% of days see measurable rain, 77°F average high, 61% of days historically clear (n=248, ERA5 2018–2025).

Seattle in August is a mixed month for sun: 61% of days historically clear (n=248, avg high 77°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 Seattle 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 Seattle 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		 68% n=120 77°F
Late August
16th–end		 55% n=128 77°F
Full month average 61% n=248 77°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 Seattle 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		 88% n=120
Late August
16th–end		 70% n=128
Full month average 79% n=248
12.5 h median sunshine per day 84% of days exceed 8 h sunshine 15% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 61%. Sunshine-based “warm & sunny”: 79%. The 18-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

Seattle clears solidly in August: 61% of days historically (n=248), avg high 77°F. Most trips here in August will find more sun than cloud.

Every month in Seattle

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

Historical clear-sky % for Seattle, 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 1% n=240 All destinations →
May 13% n=248 All destinations →
June 32% n=240 All destinations →
July 70% n=248 All destinations →
August ← this page 61% n=248 All destinations →
September 30% n=240 All destinations →
October 3% n=248 All destinations →
November 0% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Seattle in August?

Rarely. Only 15% of days in Seattle see measurable rain in August, based on 8 years of ERA5 historical data (n=248 days, 2018–2025). This is a historical average, not a forecast.

Is Seattle good for sun in August?

Yes. Seattle is historically strong for sun in August: 61% of days are clear on average (avg high 77°F, n=248 days, ERA5 2018–2025).

How Seattle compares in August

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Seattle 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.