ERA5 almanac — 8 years of real data

Mackinac Island in August

Mackinac Island in August: rain frequency data not yet backfilled for this month, 67°F average high, 3% of days historically clear (n=248, ERA5 2018–2025).

Mackinac Island in August is historically a poor month for sun: only 3% of days clear across 8 years (n=248, avg high 67°F). 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 Mackinac Island 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 Mackinac Island 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	4%	n=120	67°F
Late August 16th–end	3%	n=128	67°F
Full month average	3%	n=248	67°F

Bottom line

Mackinac Island is historically almost never clear in August: only 3% of days meet the clear bar across 8 years (n=248). Plan entirely around indoor or overcast-friendly activities.

Every month in Mackinac Island

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

Historical clear-sky % for Mackinac Island, 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	0%	n=248	All destinations →
June	0%	n=240	All destinations →
July	2%	n=248	All destinations →
August ← this page	3%	n=248	All destinations →
September	0%	n=240	All destinations →
October	0%	n=248	All destinations →
November	0%	n=240	All destinations →
December	0%	n=248	All destinations →

Frequently asked

Is Mackinac Island good for sun in August?

Not usually. Mackinac Island is historically overcast in August: only 3% of days are clear (avg high 67°F, n=248 days, ERA5 2018–2025).

→ Mackinac Island live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in August — all destinations ranked by August 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.