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SunnyDays

ERA5 almanac — 8 years of real data

Moab in September

Historically one of the better months to visit Moab for sun: 84% of days are clear on average (n=240, avg high 88°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 Moab 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 September

Clear-sky percentage for Moab in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early September
1st–15th		 80% n=120 88°F
Late September
16th–end		 87% n=120 88°F
Full month average 84% n=240 88°F

Sunshine & warmth in September

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 Moab in September. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early September
1st–15th		 97% n=120
Late September
16th–end		 98% n=120
Full month average 98% n=240
12.1 h median sunshine per day 98% of days exceed 8 h sunshine 6% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 84%. Sunshine-based “warm & sunny”: 98%. The 14-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

Moab is historically one of the best US destinations for sun in September: 84% of days meet the clear bar (avg high 88°F, n=240 days across 8 years). Pack for outdoor activity — this month consistently delivers.

Every month in Moab

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

Historical clear-sky % for Moab, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 4% n=248 All destinations →
April 46% n=240 All destinations →
May 73% n=248 All destinations →
June 88% n=240 All destinations →
July 90% n=248 All destinations →
August 84% n=248 All destinations →
September ← this page 84% n=240 All destinations →
October 41% n=248 All destinations →
November 2% n=240 All destinations →
December 0% 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.