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SunnyDays

ERA5 almanac — 8 years of real data

Scottsdale in December

Scottsdale in December is historically a poor month for sun: only 25% of days clear across 8 years (n=248, avg high 67°F). June is the clearest month for Scottsdale 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 Scottsdale 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 December

Clear-sky percentage for Scottsdale in December, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early December
1st–15th		 28% n=120 67°F
Late December
16th–end		 23% n=128 67°F
Full month average 25% n=248 67°F

Sunshine & warmth in December

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 Scottsdale in December. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early December
1st–15th		 28% n=120
Late December
16th–end		 23% n=128
Full month average 25% n=248
9.1 h median sunshine per day 77% 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: 25%. Sunshine-based “warm & sunny”: 25%. The two measures are nearly identical here — no convective-storm bias for this climate and month.

Bottom line

Scottsdale is mostly overcast in December historically: only 25% of days are clear across 8 years (n=248), avg high 67°F. If you want sun in Scottsdale, June is historically much better. Most visitors this month will see more clouds than sun.

→ See all destinations in June — historically the best month for sun in Scottsdale.

Every month in Scottsdale

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

Historical clear-sky % for Scottsdale, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 18% n=248 All destinations →
February 42% n=226 All destinations →
March 57% n=248 All destinations →
April 92% n=240 All destinations →
May 93% n=248 All destinations →
June 95% n=240 All destinations →
July 76% n=248 All destinations →
August 75% n=248 All destinations →
September 82% n=240 All destinations →
October 83% n=248 All destinations →
November 65% n=240 All destinations →
December ← this page 25% 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.