Nagano records about 801mm of rain across roughly 111 wet days a year, which is a 30% chance on an average day. June is the wettest month at 138mm (17% of the annual total) and January the driest at 18mm. Local rain type: steady rain.
Chance of rain on an average day: 30%
Rainfall climatology for Nagano. The live hour-by-hour answer for today loads at the top of this page from Open-Meteo and refreshes through the day — the figures below describe a typical year, not today.
Conditions on this page are recalculated from the latest forecast every time it is opened, for the current date in the location's own time zone. Showing .
| Annual rainfall | 801mm |
| Rain days per year | 111 |
| Odds on an average day | 30% |
| Wettest month | June — 138mm over 15 days |
| Driest month | January — 18mm over 3 days |
| Rain type | steady rain |
| Best dry window | January is the most reliable dry stretch of the year. |
| Worst rain window | June carries the highest chance of a washed-out day. |
June delivers 667% more rain than January (138mm vs 18mm). That gap is the difference between planning around showers and ignoring them.
No single month holds more than 17% of the annual total, so rain in Nagano is spread through the year — there is no season you can rely on being dry.
Nagano rain typically comes as discrete showers, so a compact umbrella and a flexible plan are usually enough.
Rain falls on about 15 days in June against 3 in January — the frequency swing matters more for planning than the millimetre totals.
Climate normals. Use them to judge whether today's live forecast at the top of the page is typical or unusual for the season.
| Month | Rainfall | Rain days | Chance on a given day | Highs |
|---|---|---|---|---|
| January | 18mm | 3 | 10% | 5°C |
| February | 18mm | 3 | 10% | 7°C |
| March | 30mm | 5 | 17% | 11°C |
| April | 54mm | 9 | 30% | 18°C |
| May | 78mm | 13 | 43% | 24°C |
| June | 138mm | 15 | 50% | 28°C |
| July | 129mm | 14 | 47% | 30°C |
| August | 120mm | 13 | 43% | 28°C |
| September | 90mm | 15 | 50% | 24°C |
| October | 66mm | 11 | 37% | 18°C |
| November | 42mm | 7 | 23% | 11°C |
| December | 18mm | 3 | 10% | 7°C |
Rain probability is the chance that at least 0.2mm falls at your location — not how long it rains. For Nagano we combine the hourly probability curve, expected volume in millimetres, and the city's own rainfall record into a single umbrella verdict.
| Factor | Weight | What it measures |
|---|---|---|
| Hourly probability | 40% | Peak and sustained chance of measurable rain across the next 24 hours. |
| Expected volume | 30% | Total millimetres, which separates a passing shower from a genuine soaking. |
| Timing & duration | 20% | When rain starts, when it eases, and the longest continuous dry window. |
| Local rain type | 10% | Drizzle, brief showers, thunderstorms or monsoon — each needs different gear. |
Live hourly values come from Open-Meteo and refresh through the day. Monthly rainfall figures are climate normals, so they describe a typical year rather than a forecast.
Nagano records rain on roughly 111 days a year — about a 30% chance on any given day — totalling around 801mm.
June, with about 138mm over 15 rain days. That is 17% of the entire year's rainfall in a single month.
January is the driest month at 18mm across roughly 3 days.
With rain on about 30% of days and steady rain as the dominant type, a compact umbrella or waterproof shell is worth packing for Nagano outside January.
No. Probability is the chance that at least 0.2mm of rain falls at your location at some point in the period. Check the expected millimetres alongside it: 40% with 0.4mm is a passing shower, 40% with 12mm is a soaking.