ERA5 almanac — 8 years of real data

San Juan Islands in July

San Juan Islands in July: 9% of days see measurable rain, 70°F average high, 26% of days historically clear (n=248, ERA5 2018–2025).

San Juan Islands in July is historically a poor month for sun: only 26% of days clear across 8 years (n=248, avg high 70°F). August is the clearest month for San Juan Islands 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 San Juan Islands 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 July

Clear-sky percentage for San Juan Islands in July, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period	% Clear days	Sample (n)	Avg high
Early July 1st–15th	22%	n=120	70°F
Late July 16th–end	29%	n=128	70°F
Full month average	26%	n=248	70°F

Sunshine & warmth in July

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 San Juan Islands in July. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period	Warm & sunny (≥72°F, >6 h sun)	Sample (n)
Early July 1st–15th	22%	n=120
Late July 16th–end	31%	n=128
Full month average	27%	n=248

14.9 h median sunshine per day 94% of days exceed 8 h sunshine 9% of days see ≥ 1 mm rain — rain is not hidden

Comparison (old vs new): WMO-code “clear” bar: 26%. Sunshine-based “warm & sunny”: 27%. The two measures are nearly identical here — no convective-storm bias for this climate and month.

Bottom line

San Juan Islands is mostly overcast in July historically: only 26% of days are clear across 8 years (n=248), avg high 70°F. If you want sun in San Juan Islands, August is historically much better. Most visitors this month will see more clouds than sun.

→ See all destinations in August — historically the best month for sun in San Juan Islands.

Every month in San Juan Islands

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

Historical clear-sky % for San Juan Islands, 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	0%	n=240	All destinations →
May	3%	n=248	All destinations →
June	10%	n=240	All destinations →
July ← this page	26%	n=248	All destinations →
August	27%	n=248	All destinations →
September	6%	n=240	All destinations →
October	1%	n=248	All destinations →
November	0%	n=240	All destinations →
December	0%	n=248	All destinations →

Frequently asked

Does it rain in San Juan Islands in July?

Rarely. Only 9% of days in San Juan Islands see measurable rain in July, based on 8 years of ERA5 historical data (n=248 days, 2018–2025). This is a historical average, not a forecast.

Is San Juan Islands good for sun in July?

Not usually. San Juan Islands is historically overcast in July: only 26% of days are clear (avg high 70°F, n=248 days, ERA5 2018–2025). August is historically far better for sun here.

How San Juan Islands compares in July

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

→ San Juan Islands vs Big Sur in July — Big Sur is 25% clear historically
→ San Juan Islands vs Yellowstone in July — Yellowstone is 24% clear historically
→ San Juan Islands vs Boundary Waters in July — Boundary Waters is 31% clear historically

→ San Juan Islands live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in July — all destinations ranked by July clear-sky %
→ All destinations
→ Raw data (JSON) — buckets, n, source

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.