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SunnyDays

ERA5 almanac — 8 years of real data

Shenandoah Valley in September

Shenandoah Valley in September: 36% of days see measurable rain, 78°F average high, 36% of days historically clear (n=240, ERA5 2018–2025).

Shenandoah Valley in September is historically a poor month for sun: only 36% of days clear across 8 years (n=240, avg high 78°F). 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 Shenandoah 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 September

Clear-sky percentage for Shenandoah Valley 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		 49% n=120 78°F
Late September
16th–end		 24% n=120 78°F
Full month average 36% n=240 78°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 Shenandoah Valley 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		 82% n=120
Late September
16th–end		 54% n=120
Full month average 68% n=240
11.6 h median sunshine per day 73% of days exceed 8 h sunshine 36% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 36%. Sunshine-based “warm & sunny”: 68%. The 32-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

Shenandoah Valley is mostly overcast in September historically: only 36% of days are clear across 8 years (n=240), avg high 78°F. The two halves differ materially (49% early, 24% late) — favour the early half of the month. Most visitors this month will see more clouds than sun.

Every month in Shenandoah Valley

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

Historical clear-sky % for Shenandoah Valley, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 1% n=226 All destinations →
March 2% n=248 All destinations →
April 14% n=240 All destinations →
May 18% n=248 All destinations →
June 39% n=240 All destinations →
July 34% n=248 All destinations →
August 34% n=248 All destinations →
September ← this page 36% n=240 All destinations →
October 17% n=248 All destinations →
November 4% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Shenandoah Valley in September?

Sometimes. Shenandoah Valley sees measurable rain on 36% of days in September historically (n=240 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Shenandoah Valley good for sun in September?

It's mixed. Shenandoah Valley in September is clear on 36% of days historically (avg high 78°F, n=240 days, ERA5 2018–2025) — the outcome varies year to year.

How Shenandoah Valley compares in September

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