Iwanai has a temperate climate with warm summers and freezing winters.
Temperatures peak in August and drop to their lowest in January, while rainfall is highest during summer months.
Humidity remains high throughout the year, especially during winter months, creating cold and damp conditions.
| Month | 🌤️ | High | Low | Avg | Humid % | Rain (mm) | Wind (m/s) | Solar (kWh/m²) |
|---|---|---|---|---|---|---|---|---|
| January | ☔ | 1.5°C | -11.6°C | -5.0°C | 92% | 115 | 3.1 | 1.33 |
| February | ☔ | 1.7°C | -11.6°C | -4.9°C | 90% | 88 | 3.4 | 2.04 |
| March | ❄️ | 6.0°C | -9.5°C | -1.8°C | 87% | 71 | 2.9 | 3.27 |
| April | 🌨️ | 15.2°C | -3.3°C | 5.9°C | 82% | 62 | 2.1 | 4.44 |
| May | 🌤️ | 20.6°C | 1.3°C | 11.0°C | 81% | 71 | 1.4 | 5.03 |
| June | ☀️ | 24.0°C | 6.6°C | 15.3°C | 83% | 71 | 1.0 | 5.04 |
| July | ☔ | 27.3°C | 11.6°C | 19.4°C | 85% | 98 | 0.9 | 4.57 |
| August | ☔ | 29.0°C | 13.9°C | 21.4°C | 84% | 147 | 1.1 | 4.27 |
| September | ☔ | 25.3°C | 9.0°C | 17.2°C | 82% | 137 | 1.4 | 3.76 |
| October | ☔ | 19.6°C | 2.2°C | 10.9°C | 81% | 127 | 1.7 | 2.73 |
| November | ☔ | 13.6°C | -4.8°C | 4.4°C | 85% | 139 | 2.1 | 1.56 |
| December | ☔ | 5.9°C | -9.6°C | -1.9°C | 91% | 137 | 2.6 | 1.14 |
Showing average climate conditions across 45 years (1981–2025)
🧥 Pack heavy layers and prepare for snow — this is a Severe Winter destination.
🌤️ Conditions are ideal for outdoor activities throughout the day in this Mild Summer.
☔ Moderate Rainfall expected — carry rain gear and plan outdoor activities around these months.
Monthly averages · 1981–2025 climate normals · °C
Temperatures rise steadily from spring, peak in August, and gradually decline through autumn into winter.
These seasonal patterns make summer ideal for outdoor activities, while winters bring freezing conditions and heavy snowfall.
Monthly rainfall · 1981–2025 seasonal trends · mm/month
Rainfall is concentrated in the summer months. Humidity stays high (around 85%), peaking during winter months, which creates cold and damp conditions.
☔ Moderate Rainfall expected — carry rain gear and plan outdoor activities around these months.
Monthly averages · 1981–2025
Across 45 years of records, Iwanai's temperature has remained relatively stable over the past decade. Its hottest day reached 34.5°C in July 2025, and its coldest dropped to -15.7°C in January 1985. 2025 was the warmest year overall and 2001 the coolest.
The warmest year in Iwanai's recorded history was 2025 (avg: 9.5°C), while the coldest was 2001 (avg: 6.5°C).
Average annual high/low · Last 30 years · °C
Total annual precipitation · Last 30 years · mm/year
| Year | Min Temp | Avg Temp | Max Temp | Rainfall (mm) | Avg Humidity | Avg Wind |
|---|---|---|---|---|---|---|
2025 🔥 🌧️ | 1.0°C | 9.5°C | 17.9°C | 1637 | 87% | 2.0 m/s |
2024 | 0.7°C | 8.7°C | 16.7°C | 1462 | 86% | 1.9 m/s |
2023 | 0.6°C | 9.1°C | 17.5°C | 1463 | 86% | 1.9 m/s |
2022 | -0.6°C | 7.5°C | 15.6°C | 1479 | 86% | 1.8 m/s |
2021 | -0.8°C | 8.1°C | 17.0°C | 1453 | 86% | 1.9 m/s |
2020 | 0.1°C | 8.0°C | 15.9°C | 1295 | 86% | 1.8 m/s |
2019 | -0.8°C | 7.9°C | 16.6°C | 1044 | 84% | 1.9 m/s |
2018 | -0.7°C | 7.8°C | 16.4°C | 1613 | 86% | 1.9 m/s |
2017 | -1.0°C | 6.9°C | 14.7°C | 1427 | 86% | 1.9 m/s |
2016 | -0.9°C | 7.7°C | 16.2°C | 1505 | 86% | 2.0 m/s |
Showing 1 to 10 of 45 years
Based on 45 years of data (1981–2025), August is typically the hottest month in Iwanai, Hokkaidō, with average high temperatures around 29.0°C.
January is the coldest month in Iwanai, with average low temperatures around -11.6°C.
August receives the most rainfall with approximately 147 mm, while April is the driest with 62 mm.
The highest recorded temperature was 34.5°C in July 2025. This is part of the historical record spanning 1981–2025.
The lowest recorded temperature was -15.7°C in January 1985.
This page covers 45 years of climate data from 1981 to 2025. As new data is added to the database the page automatically reflects the updated coverage.
Iwanai receives the most sunlight in June with an average solar radiation of 5.04 kWh/m²/day. This solar radiation data, sourced from NASA POWER, is useful for solar energy planning and agriculture in Hokkaidō.
All climate data is sourced from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite and model data. It provides monthly averages for temperature, precipitation, humidity, wind speed, and solar radiation.
All weather data is sourced from NASA POWER (Prediction of Worldwide Energy Resources), a NASA project providing solar and meteorological data for renewable energy, building efficiency, and agricultural research.
