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SunnyDays

ERA5 almanac — 8 years of real data

Yellowstone in August

Yellowstone in August: 31% of days see measurable rain, 69°F average high, 19% of days historically clear (n=248, ERA5 2018–2025).

Yellowstone in August is historically a poor month for sun: only 19% of days clear across 8 years (n=248, avg high 69°F). July is the clearest month for Yellowstone 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 Yellowstone 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 Yellowstone 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		 22% n=120 69°F
Late August
16th–end		 16% n=128 69°F
Full month average 19% n=248 69°F

Sunshine & warmth in August

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 Yellowstone in August. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early August
1st–15th		 44% n=120
Late August
16th–end		 34% n=128
Full month average 39% n=248
13.2 h median sunshine per day 93% of days exceed 8 h sunshine 31% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 19%. Sunshine-based “warm & sunny”: 39%. The 20-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

Yellowstone is a poor choice for sun in August: just 19% of days clear historically (n=248). July is the historically strongest month for sun here. The 8-year record is consistent — this is not a fluke bad stretch.

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

Every month in Yellowstone

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

Historical clear-sky % for Yellowstone, 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 4% n=240 All destinations →
July 24% n=248 All destinations →
August ← this page 19% 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

Does it rain in Yellowstone in August?

Sometimes. Yellowstone sees measurable rain on 31% of days in August historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Yellowstone good for sun in August?

Not usually. Yellowstone is historically overcast in August: only 19% of days are clear (avg high 69°F, n=248 days, ERA5 2018–2025). July is historically far better for sun here.

How Yellowstone compares in August

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

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.