ERA5 almanac — 8 years of real data

Martha's Vineyard in July

Martha's Vineyard in July: 33% of days see measurable rain, 78°F average high, 45% of days historically clear (n=248, ERA5 2018–2025).

Martha's Vineyard in July is a mixed month for sun: 45% of days historically clear (n=248, avg high 78°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 Martha's Vineyard 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 Martha's Vineyard 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	47%	n=120	78°F
Late July 16th–end	44%	n=128	78°F
Full month average	45%	n=248	78°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 Martha's Vineyard 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	85%	n=120
Late July 16th–end	88%	n=128
Full month average	87%	n=248

13.0 h median sunshine per day 88% of days exceed 8 h sunshine 33% of days see ≥ 1 mm rain — rain is not hidden

Comparison (old vs new): WMO-code “clear” bar: 45%. Sunshine-based “warm & sunny”: 87%. The 42-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

Martha's Vineyard in July is genuinely mixed: 45% of days historically clear (n=248), avg high 78°F — roughly even odds. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Martha's Vineyard

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

Historical clear-sky % for Martha's Vineyard, 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	25%	n=240	All destinations →
July ← this page	45%	n=248	All destinations →
August	46%	n=248	All destinations →
September	27%	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 Martha's Vineyard in July?

Sometimes. Martha's Vineyard sees measurable rain on 33% of days in July historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Martha's Vineyard good for sun in July?

It's mixed. Martha's Vineyard in July is clear on 45% of days historically (avg high 78°F, n=248 days, ERA5 2018–2025) — the outcome varies year to year.

How Martha's Vineyard compares in July

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

→ Martha's Vineyard vs San Antonio in July — San Antonio is 44% clear historically
→ Martha's Vineyard vs The Hamptons in July — The Hamptons is 44% clear historically
→ Martha's Vineyard vs Traverse City in July — Traverse City is 44% clear historically

→ Martha's Vineyard 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.