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SunnyDays

ERA5 almanac — 8 years of real data

Sun Valley in August

Sun Valley in August: 17% of days see measurable rain, 80°F average high, 58% of days historically clear (n=248, ERA5 2018–2025).

Sun Valley in August is a mixed month for sun: 58% of days historically clear (n=248, avg high 80°F). The outcome varies year to year — check the early/late split below. 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 Sun Valley 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 Sun Valley 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		 63% n=120 80°F
Late August
16th–end		 54% n=128 80°F
Full month average 58% n=248 80°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 Sun Valley 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		 95% n=120
Late August
16th–end		 84% n=128
Full month average 89% n=248
13.3 h median sunshine per day 98% of days exceed 8 h sunshine 17% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 58%. Sunshine-based “warm & sunny”: 89%. The 31-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

Sun Valley in August is genuinely mixed: 58% of days historically clear (n=248), avg high 80°F — more clear than cloudy. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Sun Valley

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

Historical clear-sky % for Sun Valley, 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 3% n=248 All destinations →
June 33% n=240 All destinations →
July 70% n=248 All destinations →
August ← this page 58% n=248 All destinations →
September 42% n=240 All destinations →
October 3% n=248 All destinations →
November 0% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Sun Valley in August?

Rarely. Only 17% of days in Sun Valley see measurable rain in August, based on 8 years of ERA5 historical data (n=248 days, 2018–2025). This is a historical average, not a forecast.

Is Sun Valley good for sun in August?

It's mixed. Sun Valley in August is clear on 58% of days historically (avg high 80°F, n=248 days, ERA5 2018–2025) — the outcome varies year to year.

How Sun Valley compares in August

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Sun Valley 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.