ERA5 almanac comparison — 8 years of real data
Phoenix vs Tulum: weather in December
Essentially a tie in December: Phoenix is 22% clear historically, Tulum is 21% clear (8-year ERA5 average) — within the noise. Avg high 67°F vs 81°F. Tulum also sees measurably more rain than Phoenix this month (49% vs 13% of days). Pick based on flight time or price, not weather — the weather won't decide this one for you.
Phoenix
AZ
- Clear days, December
- 22%
- Sample size
- n=248 days
- Avg high
- 67°F
- Early December (1st–15th)
- 25%
- Late December (16th–end)
- 20%
- Rain frequency
- 13% of days
Tulum
MX
- Clear days, December
- 21%
- Sample size
- n=248 days
- Avg high
- 81°F
- Early December (1st–15th)
- 21%
- Late December (16th–end)
- 21%
- Rain frequency
- 49% of days
Compare Phoenix vs Tulum in another month
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.