Iiyama Temperature by Month

Iiyama in Nagano Prefecture, Japan sees significant seasonal temperature differences, with daytime highs between 3°C (37°F) in January and 29°C (84°F) in August, averaging 16°C (61°F) annually. Explore the full monthly breakdown below.

The weather in Iiyama experiences significant differences between warm and cold seasons, with big shifts in temperature. At night, minimum temperatures range from 20°C (68°F) in August to -5°C (23°F) in January.

The chart below illustrates the average maximum day and minimum night temperatures in Iiyama by month:

The minimum temperature is often recorded between 4 AM and 6 AM, while the highest temperature is usually reached at 3 PM, when the sun's heating effect is strongest. August, the warmest month, gets 197 hours of sunshine.

The chart below shows the average temperature throughout the year:

Iiyama's average annual maximum temperature is 16°C (61°F). To put that in context, here's how it compares to a few well-known destinations:

Seville, Spain averages 23°C (73°F) a year, one of the warmer cities in Western Europe, with long hot summers.

On the cooler end, Oslo, Norway averages just 10°C (50°F) annually, with pleasant summers but long, cold winters.

San Francisco, USA averages 19°C (66°F) annually, but with little seasonal variation, summers are often cool and foggy, winters mild.

Perth, Australia averages 25°C (77°F) annually, with a classic Mediterranean climate, hot dry summers and mild wet winters.

Temperature alone doesn't tell the whole story, humidity plays a big role in how warm or cold it actually feels. High humidity in summer makes the heat feel more intense, particularly once temperatures climb above 25°C. In winter, the same humidity can make cold air feel sharper than the thermometer suggests.

In the cooler months, when temperatures drop below 10°C, high humidity makes the cold feel more cutting than it would in dry conditions.

In Iiyama, January is the coolest month, with average highs of 3°C (37°F) and humidity around 78%, considered high. In August, the warmest month, temperatures average 29°C (84°F) with 77% humidity, conditions that feel high. For a full picture, see our humidity page.

Climate temperature data is typically calculated as a 30-year average. This smooths out year-to-year variability and gives a more reliable picture of what a place is actually like, rather than what happened in any single unusual year.

The readings come from a range of sources, land-based weather stations, ocean buoys, ships, and satellites. That data is collected by weather services around the world, then pooled, quality-checked, and averaged to produce the climate records you see here.

Global average temperatures have risen by around 1.2°C since the pre-industrial era, and the effects are visible across many regions. Winters are milder on average, with fewer frost days and less snow in many parts of the world. Heatwaves are more frequent and more intense, and Europe's summers of 2018, 2019, and 2020 all set records.

Summers are also getting drier in some areas, while winter rainfall has increased in others. This contributies to higher river levels and more flooding. In many countries, spring arrives earlier and autumn lasts longer. It has knock-on effects for wildlife, agriculture, and local ecosystems.

For more on Iiyama's weather, including monthly rainfall, sunshine hours, and humidity, visit our Iiyama climate page.