ERA5 almanac — 8 years of real data

Big Sky in June

Big Sky in June: rain frequency data not yet backfilled for this month, 60°F average high, 2% of days historically clear (n=240, ERA5 2018–2025).

Big Sky in June is historically a poor month for sun: only 2% of days clear across 8 years (n=240, avg high 60°F). July is the clearest month for Big Sky 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 Big Sky 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 June

Clear-sky percentage for Big Sky in June, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period	% Clear days	Sample (n)	Avg high
Early June 1st–15th	2%	n=120	60°F
Late June 16th–end	3%	n=120	60°F
Full month average	2%	n=240	60°F

Bottom line

Big Sky is historically almost never clear in June: only 2% of days meet the clear bar across 8 years (n=240). Come back in July if you want clear skies here. Plan entirely around indoor or overcast-friendly activities.

→ See all destinations in July — historically the best month for sun in Big Sky.

Every month in Big Sky

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

Historical clear-sky % for Big Sky, 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 ← this page	2%	n=240	All destinations →
July	18%	n=248	All destinations →
August	18%	n=248	All destinations →
September	8%	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 Big Sky good for sun in June?

Not usually. Big Sky is historically overcast in June: only 2% of days are clear (avg high 60°F, n=240 days, ERA5 2018–2025). July is historically far better for sun here.

→ Big Sky live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in June — all destinations ranked by June 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.