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SunnyDays

ERA5 almanac — 8 years of real data

Missoula in May

Missoula in May: 26% of days see measurable rain, 68°F average high, 22% of days historically clear (n=248, ERA5 2018–2025).

Missoula in May is historically a poor month for sun: only 22% of days clear across 8 years (n=248, avg high 68°F). July is the clearest month for Missoula 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 Missoula 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 May

Clear-sky percentage for Missoula in May, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early May
1st–15th		 21% n=120 68°F
Late May
16th–end		 23% n=128 68°F
Full month average 22% n=248 68°F

Sunshine & warmth in May

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 Missoula in May. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early May
1st–15th		 29% n=120
Late May
16th–end		 41% n=128
Full month average 35% n=248
13.4 h median sunshine per day 84% of days exceed 8 h sunshine 26% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 22%. Sunshine-based “warm & sunny”: 35%. The 13-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

Missoula is mostly overcast in May historically: only 22% of days are clear across 8 years (n=248), avg high 68°F. If you want sun in Missoula, July is historically much better. Most visitors this month will see more clouds than sun.

→ See all destinations in July — historically the best month for sun in Missoula.

Every month in Missoula

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

Historical clear-sky % for Missoula, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 0% n=248 All destinations →
April 4% n=240 All destinations →
May ← this page 22% n=248 All destinations →
June 44% n=240 All destinations →
July 82% n=248 All destinations →
August 74% n=248 All destinations →
September 57% n=240 All destinations →
October 14% n=248 All destinations →
November 0% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Missoula in May?

Sometimes. Missoula sees measurable rain on 26% of days in May historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Missoula good for sun in May?

Not usually. Missoula is historically overcast in May: only 22% of days are clear (avg high 68°F, n=248 days, ERA5 2018–2025). July is historically far better for sun here.

How Missoula compares in May

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