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SunnyDays

ERA5 almanac — 8 years of real data

Phoenix in August

Historically one of the better months to visit Phoenix for sun: 76% of days are clear on average (n=248, avg high 106°F). Every percentage here is a historical average from 8 years of ERA5 data — 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 Phoenix 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 Phoenix 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		 76% n=120 106°F
Late August
16th–end		 76% n=128 106°F
Full month average 76% n=248 106°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 Phoenix 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		 100% n=120
Late August
16th–end		 98% n=128
Full month average 99% n=248
12.9 h median sunshine per day 97% of days exceed 8 h sunshine 13% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 76%. Sunshine-based “warm & sunny”: 99%. The 23-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

Phoenix clears solidly in August: 76% of days historically (n=248), avg high 106°F. Most trips here in August will find more sun than cloud.

Every month in Phoenix

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

Historical clear-sky % for Phoenix, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 17% n=248 All destinations →
February 41% n=226 All destinations →
March 61% n=248 All destinations →
April 94% n=240 All destinations →
May 95% n=248 All destinations →
June 94% n=240 All destinations →
July 76% n=248 All destinations →
August ← this page 76% n=248 All destinations →
September 82% n=240 All destinations →
October 85% n=248 All destinations →
November 63% n=240 All destinations →
December 22% n=248 All destinations →

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.