Temperature records for Iiyama (Nagano)
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― on the normal curve
Monthly normals for Iiyama
Temperature (monthly normals)
The lines show monthly normals: the upper line is the monthly mean of the daily high and the lower line the monthly mean of the daily low, and the middle line is the monthly mean temperature. Touch the point for a month to read its values. Normals are the 1991–2020 average.
Precipitation (monthly normals, mm)
Table of monthly normals
| Month | Mean | High | Low | Precipitation |
|---|---|---|---|---|
| Jan | -1.6 | 2.5 | -6.2 | 171.8 |
| Feb | -1.2 | 3.6 | -6.3 | 117.3 |
| Mar | 2.4 | 8.0 | -2.7 | 96.2 |
| Apr | 9.3 | 16.1 | 3.3 | 63.1 |
| May | 15.7 | 22.5 | 9.4 | 69.2 |
| Jun | 19.9 | 25.6 | 15.1 | 101.4 |
| Jul | 23.7 | 29.1 | 19.7 | 155.7 |
| Aug | 24.7 | 30.6 | 20.4 | 128.8 |
| Sep | 20.4 | 26.0 | 16.1 | 127.2 |
| Oct | 13.8 | 19.7 | 9.1 | 117.2 |
| Nov | 7.2 | 13.0 | 2.6 | 96.8 |
| Dec | 1.4 | 5.9 | -2.5 | 167.4 |
Temperatures are in degrees Celsius (°C) and precipitation in mm. Blank cells have no normal.
Annual mean temperature (1996–2025)
The yearly average of the daily mean temperature (the line is broken in years with many missing values). This station's observing conditions changed on January 1, 2003; November 10, 2005; October 9, 2008; March 2, 2021 (for example, a relocation or new instruments), so the statistics may not be continuous across those dates.
The normals listed here are averages over the 30 years from 1991 to 2020. They are fixed values that stay the same until the next revision of the normals, and they show how warm or cold that month usually is in that area.
All-time records
Records are statistics as of November 1, 2026. The statistical period differs by element, depending on when observations began or the station moved.
| Record | Value | Date | Records began |
|---|---|---|---|
| Highest temperature | 37.6°C | Aug 14, 1994 | Nov 1978 |
| Lowest temperature | -19.7°C | Feb 5, 1999 | Nov 1978 |
| Highest daily minimum | 26.2°C | Aug 23, 1990 | Nov 1978 |
| Lowest daily maximum | -5.5°C | Jan 18, 1981 | Nov 1978 |
| Heaviest daily rainfall | 162.0 mm | Sep 3, 1986 | Jan 1976 |
Top 5 highest temperatures
| Rank | Value | Date |
|---|---|---|
| 1 | 37.6°C | Aug 14, 1994 |
| 2 | 37.4°C | Aug 22, 2018 |
| 3 | 37.2°C | Aug 4, 2025 |
| 4 | 37.2°C | Jul 4, 2004 |
| 5 | 37.0°C | Aug 19, 2004 |
12-month dry-day calendar
The dry-day rate is the share of years with no precipitation (rain or snow) of 1 mm or more on that day (daily precipitation under 1 mm, smoothed over 4 days either side). It is based on observations for 1996–2025 (30 years).
The deeper the amber, the more years that day stayed dry (the legend above shows the colors). Each row ends with the monthly average; detailed values are in the monthly table below.
Monthly averages through the year
How the monthly average dry-day rate changes over the 12 months (the axis fits the range of values). The values match the monthly table below.
Monthly table of dry-day rates and climate
| Month | Dry-day rate | 2 days in a row | 3 days in a row | Windy days | Sunshine (avg.) | High (avg.) | Low (avg.) | Comfort |
|---|---|---|---|---|---|---|---|---|
| Jan | 37.4% | 16.7% | 8.4% | 0.2% | 2.6 h | 2.4°C | -6.1°C | Harsh |
| Feb | 44.3% | 24.2% | 13.6% | 0.4% | 3.6 h | 3.7°C | -6.0°C | Harsh |
| Mar | 55.6% | 34.4% | 21.3% | 1.3% | 4.7 h | 8.4°C | -2.3°C | Tough |
| Apr | 66.5% | 47.9% | 34.2% | 2.6% | 5.9 h | 16.2°C | 3.5°C | Comfortable |
| May | 70.4% | 52.0% | 37.2% | 2.1% | 6.2 h | 22.6°C | 9.7°C | Comfortable |
| Jun | 65.5% | 47.4% | 34.1% | 0.4% | 5.1 h | 25.8°C | 15.4°C | Comfortable |
| Jul | 58.7% | 40.7% | 29.8% | 0.1% | 5.1 h | 29.4°C | 20.1°C | Good |
| Aug | 67.1% | 50.6% | 38.9% | 0.4% | 6.2 h | 30.7°C | 20.8°C | Fair |
| Sep | 61.4% | 42.1% | 28.9% | 0.9% | 4.8 h | 26.4°C | 16.7°C | Comfortable |
| Oct | 63.9% | 44.8% | 30.5% | 0.4% | 4.2 h | 19.7°C | 9.3°C | Comfortable |
| Nov | 57.7% | 36.9% | 23.8% | 0.8% | 3.5 h | 13.1°C | 3.0°C | Fair |
| Dec | 44.8% | 22.6% | 10.9% | 0.1% | 2.8 h | 5.9°C | -2.3°C | Harsh |
"2 days in a row" and "3 days in a row" are the monthly averages of the share of years in which it stayed dry for 2 or 3 days from that day (counted from the actual consecutive records). "Windy days" is the share of days with a daily mean wind speed of 5 m/s or more. Sunshine averages include estimates from March 2021 onward at some stations. The month names link to monthly pages that compare stations across Japan.
Comfort over the 12 months
A guide that rates the comfort of each month on 5 levels from observations of dry-day rate, sunshine, wind, and temperature for 1996–2025 (30 years). The levels are also in the monthly table above.
This station's observing conditions changed on January 1, 2003; November 10, 2005; October 9, 2008; March 2, 2021 (for example, a relocation or new instruments), so the statistics may not be continuous across those dates.
These are statistics compiled from observations for 1996–2025 (30 years), not a weather forecast for any particular day. For the latest forecasts, see the JMA website.
Compare and explore
Nearby stations: Nozawa Onsen (about 7 km) / Shinano-Machi (about 18 km) / Takada (about 28 km)
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