ERA5 almanac — 8 years of real data

Denver in May

Denver in May: 36% of days see measurable rain, 72°F average high, 33% of days historically clear (n=248, ERA5 2018–2025).

Denver in May is historically a poor month for sun: only 33% of days clear across 8 years (n=248, avg high 72°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 Denver 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 May

Clear-sky percentage for Denver in May, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period	% Clear days	Sample (n)	Avg high
Early May 1st–15th	28%	n=120	72°F
Late May 16th–end	37%	n=128	72°F
Full month average	33%	n=248	72°F

Sunshine & warmth in May

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 Denver in May. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period	Warm & sunny (≥72°F, >6 h sun)	Sample (n)
Early May 1st–15th	43%	n=120
Late May 16th–end	67%	n=128
Full month average	55%	n=248

13.0 h median sunshine per day 83% of days exceed 8 h sunshine 36% of days see ≥ 1 mm rain — rain is not hidden

Comparison (old vs new): WMO-code “clear” bar: 33%. Sunshine-based “warm & sunny”: 55%. The 22-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

Denver is mostly overcast in May historically: only 33% of days are clear across 8 years (n=248), avg high 72°F. Most visitors this month will see more clouds than sun.

Every month in Denver

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

Historical clear-sky % for Denver, all months, ERA5 2018–2025.
Month	% Clear	Sample (n)
January	0%	n=248	All destinations →
February	0%	n=226	All destinations →
March	2%	n=248	All destinations →
April	22%	n=240	All destinations →
May ← this page	33%	n=248	All destinations →
June	56%	n=240	All destinations →
July	52%	n=248	All destinations →
August	59%	n=248	All destinations →
September	74%	n=240	All destinations →
October	38%	n=248	All destinations →
November	6%	n=240	All destinations →
December	1%	n=248	All destinations →

Frequently asked

Does it rain in Denver in May?

Sometimes. Denver sees measurable rain on 36% of days in May historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Denver good for sun in May?

It's mixed. Denver in May is clear on 33% of days historically (avg high 72°F, n=248 days, ERA5 2018–2025) — the outcome varies year to year.

How Denver compares in May

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

→ Denver vs Key West in May — Key West is 33% clear historically
→ Denver vs Mexico City in May — Mexico City is 33% clear historically
→ Denver vs Atlanta in May — Atlanta is 32% clear historically

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