ERA5 almanac — 8 years of real data

Whistler in September

Whistler in September: rain frequency data not yet backfilled for this month, 68°F average high, 28% of days historically clear (n=240, ERA5 2018–2025).

Whistler in September is historically a poor month for sun: only 28% of days clear across 8 years (n=240, avg high 68°F). July is the clearest month for Whistler 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 Whistler 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 September

Clear-sky percentage for Whistler in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period	% Clear days	Sample (n)	Avg high
Early September 1st–15th	41%	n=120	68°F
Late September 16th–end	16%	n=120	68°F
Full month average	28%	n=240	68°F

Bottom line

Whistler is mostly overcast in September historically: only 28% of days are clear across 8 years (n=240), avg high 68°F. The two halves differ materially (41% early, 16% late) — favour the early half of the month. If you want sun in Whistler, July is historically much better. Most visitors this month will see more clouds than sun.

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

Every month in Whistler

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

Historical clear-sky % for Whistler, 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	11%	n=248	All destinations →
June	21%	n=240	All destinations →
July	50%	n=248	All destinations →
August	48%	n=248	All destinations →
September ← this page	28%	n=240	All destinations →
October	8%	n=248	All destinations →
November	0%	n=240	All destinations →
December	0%	n=248	All destinations →

Frequently asked

Is Whistler good for sun in September?

Not usually. Whistler is historically overcast in September: only 28% of days are clear (avg high 68°F, n=240 days, ERA5 2018–2025). July is historically far better for sun here.

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