Iiyama weather in December
In December, Iiyama sees average daytime highs of 5°C and overnight lows near -3°C, with 138 mm of precipitation across 20.4 wet days and about 9.5 hours of daylight. It is the 10th-warmest and 7th-wettest month of the year here.
Highs ease over the month, from about 7°C in the first days to 2°C by the end. The sky is clear or mostly clear about 17% of the time in December, and the air most often feels dry.
Daylight stretches from about 9 h 42 min at the start of December to 9 h 30 min by month's end. Set against the rest of the year, December is Iiyama's 4th-clearest and 6th-windiest month. For the whole year in context, see Iiyama's year-round climate.
- Daytime high
- 5°
- 10th warmest
- Overnight low
- -3°
- 3rd coldest
- Precipitation
- 138 mm
- 20.4 wet days
- Daylight
- 9 h 30 min
- 6:58 AM – 4:27 PM
- Cloud cover
- 65%
- 4th clearest
- Wind
- 5 km/h
- 6th windiest
- Solar energy
- 2.15 kWh/m²
- Travel score
- 0.2
- out of 10
Iiyama is city in Nagano Prefecture, Japan.
- Density
- 99/km²
- people per km²
- Founded
- 1954
Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.
Temperature in December
Highs ease over the month, from about 7°C in the first days to 2°C by the end.
A typical December day in Iiyama reaches about 5°C in the afternoon and slips back to -3°C overnight — a 8°C spread between the day's warmth and the night's chill. On most days the high lands between -0°C and 9°C. Set against its neighbours, December runs about 6°C cooler than November and about 3°C warmer than January.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 8 | 7 | 7 | 7 | 7 | 6 | 6 | 6 | 6 | 5 | 5 | 5 | 5 | 5 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 2 | 2 |
| Avg low (°C) | -1 | -1 | -1 | -1 | -1 | -2 | -2 | -2 | -2 | -2 | -3 | -3 | -3 | -3 | -3 | -3 | -3 | -4 | -4 | -4 | -4 | -4 | -4 | -4 | -4 | -5 | -5 | -5 | -5 | -5 | -5 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| 1 | 8 | -1 |
| 2 | 7 | -1 |
| 3 | 7 | -1 |
| 4 | 7 | -1 |
| 5 | 7 | -1 |
| 6 | 6 | -2 |
| 7 | 6 | -2 |
| 8 | 6 | -2 |
| 9 | 6 | -2 |
| 10 | 5 | -2 |
| 11 | 5 | -3 |
| 12 | 5 | -3 |
| 13 | 5 | -3 |
| 14 | 5 | -3 |
| 15 | 4 | -3 |
| 16 | 4 | -3 |
| 17 | 4 | -3 |
| 18 | 4 | -4 |
| 19 | 4 | -4 |
| 20 | 4 | -4 |
| 21 | 4 | -4 |
| 22 | 3 | -4 |
| 23 | 3 | -4 |
| 24 | 3 | -4 |
| 25 | 3 | -4 |
| 26 | 3 | -5 |
| 27 | 3 | -5 |
| 28 | 3 | -5 |
| 29 | 3 | -5 |
| 30 | 2 | -5 |
| 31 | 2 | -5 |
How December really feels in Iiyama
Once humidity and wind are folded in, December averages 0 days that feel above 32°C and 31 that feel at or below 0°C — the comfort signal a plain temperature reading hides.
The story in December is cold — wind chill drags the overnight "feels like" below the raw low.
Iiyama weather by month
How December compares with the rest of the year at a glance. December is the 10th-warmest and 7th-wettest month here — the current month is highlighted below.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | 2° / -6° | 147 | 22.8 | 23.4 | 9.8 | 0.0 |
| Feb | 2° / -5° | 120 | 18.9 | 18.5 | 10.6 | 0.0 |
| Mar | 6° / -2° | 138 | 18.6 | 14.8 | 11.7 | 0.6 |
| Apr | 13° / 3° | 115 | 14.6 | 3.5 | 12.9 | 3.4 |
| May | 19° / 9° | 133 | 14.7 | 0.1 | 13.9 | 5.5 |
| Jun | 23° / 14° | 178 | 18.1 | 0 | 14.5 | 5.2 |
| Jul | 26° / 18° | 243 | 21.7 | 0 | 14.3 | 4.7 |
| Aug | 27° / 19° | 169 | 19.6 | 0 | 13.4 | 4.9 |
| Sep | 23° / 15° | 182 | 17 | 0 | 12.3 | 5.4 |
| Oct | 17° / 8° | 161 | 15.6 | 0.1 | 11 | 4.7 |
| Nov | 11° / 2° | 116 | 16.4 | 4.6 | 10 | 2.3 |
| Dec | 5° / -3° | 138 | 20.4 | 17 | 9.5 | 0.2 |
Cloud cover in December
The sky is clear or mostly clear about 17% of the time in December.
Beyond those clear spells, partly cloudy skies cover about 19% of December, with mostly cloudy or overcast conditions the remaining 64%.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 38 | 38 | 37 | 37 | 36 | 36 | 36 | 35 | 35 | 34 | 34 | 34 | 35 | 35 | 34 | 34 | 35 | 36 | 36 | 36 | 37 | 36 | 36 | 37 | 37 | 37 | 35 | 35 | 35 | 34 | 34 |
| Cloudier (%) | 62 | 62 | 63 | 63 | 64 | 64 | 64 | 65 | 65 | 66 | 66 | 66 | 65 | 65 | 66 | 66 | 65 | 64 | 64 | 64 | 63 | 64 | 64 | 63 | 63 | 63 | 65 | 65 | 65 | 66 | 66 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| 1 | 38 | 62 |
| 2 | 38 | 62 |
| 3 | 37 | 63 |
| 4 | 37 | 63 |
| 5 | 36 | 64 |
| 6 | 36 | 64 |
| 7 | 36 | 64 |
| 8 | 35 | 65 |
| 9 | 35 | 65 |
| 10 | 34 | 66 |
| 11 | 34 | 66 |
| 12 | 34 | 66 |
| 13 | 35 | 65 |
| 14 | 35 | 65 |
| 15 | 34 | 66 |
| 16 | 34 | 66 |
| 17 | 35 | 65 |
| 18 | 36 | 64 |
| 19 | 36 | 64 |
| 20 | 36 | 64 |
| 21 | 37 | 63 |
| 22 | 36 | 64 |
| 23 | 36 | 64 |
| 24 | 37 | 63 |
| 25 | 37 | 63 |
| 26 | 37 | 63 |
| 27 | 35 | 65 |
| 28 | 35 | 65 |
| 29 | 35 | 65 |
| 30 | 34 | 66 |
| 31 | 34 | 66 |
Chance of precipitation in December
Iiyama gets around 138 mm of rain and snow over 20.4 wet days in December. The line is the day-by-day chance of measurable precipitation.
Day to day, the chance of measurable precipitation averages around 66% and peaks near 72% on the wettest days, and about 17 days bring snow. The odds climb toward the end of the month.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain chance (%) | 60 | 61 | 62 | 63 | 63 | 64 | 64 | 65 | 65 | 66 | 66 | 66 | 66 | 66 | 66 | 66 | 66 | 66 | 66 | 66 | 66 | 66 | 67 | 67 | 68 | 68 | 69 | 70 | 70 | 71 | 72 |
| Snow chance (%) | 35 | 37 | 38 | 40 | 42 | 44 | 46 | 47 | 49 | 50 | 52 | 53 | 54 | 54 | 55 | 55 | 56 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 66 | 67 | 68 | 69 | 71 |
| Rain chance (%) | Snow chance (%) | |
|---|---|---|
| 1 | 60 | 35 |
| 2 | 61 | 37 |
| 3 | 62 | 38 |
| 4 | 63 | 40 |
| 5 | 63 | 42 |
| 6 | 64 | 44 |
| 7 | 64 | 46 |
| 8 | 65 | 47 |
| 9 | 65 | 49 |
| 10 | 66 | 50 |
| 11 | 66 | 52 |
| 12 | 66 | 53 |
| 13 | 66 | 54 |
| 14 | 66 | 54 |
| 15 | 66 | 55 |
| 16 | 66 | 55 |
| 17 | 66 | 56 |
| 18 | 66 | 56 |
| 19 | 66 | 57 |
| 20 | 66 | 58 |
| 21 | 66 | 59 |
| 22 | 66 | 60 |
| 23 | 67 | 61 |
| 24 | 67 | 62 |
| 25 | 68 | 63 |
| 26 | 68 | 64 |
| 27 | 69 | 66 |
| 28 | 70 | 67 |
| 29 | 70 | 68 |
| 30 | 71 | 69 |
| 31 | 72 | 71 |
Humidity in December
Most of December feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.
By dew point, December lands in the dry band about 100% of days. It rarely turns muggy — the humid and sticky bands barely register.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
| Dry (%) | |
|---|---|
| 1 | 100 |
| 2 | 100 |
| 3 | 100 |
| 4 | 100 |
| 5 | 100 |
| 6 | 100 |
| 7 | 100 |
| 8 | 100 |
| 9 | 100 |
| 10 | 100 |
| 11 | 100 |
| 12 | 100 |
| 13 | 100 |
| 14 | 100 |
| 15 | 100 |
| 16 | 100 |
| 17 | 100 |
| 18 | 100 |
| 19 | 100 |
| 20 | 100 |
| 21 | 100 |
| 22 | 100 |
| 23 | 100 |
| 24 | 100 |
| 25 | 100 |
| 26 | 100 |
| 27 | 100 |
| 28 | 100 |
| 29 | 100 |
| 30 | 100 |
| 31 | 100 |
Wind in December
Winds average 5 km/h in December.
Across December, daily wind ranges from about 5 km/h on the calmest days to 5 km/h at its breeziest. It stays fairly steady from day to day.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (km/h) | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 |
| Feels | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm | calm |
| Wind speed (km/h) | Feels | |
|---|---|---|
| 1 | 5 | calm |
| 2 | 5 | calm |
| 3 | 5 | calm |
| 4 | 5 | calm |
| 5 | 5 | calm |
| 6 | 5 | calm |
| 7 | 5 | calm |
| 8 | 5 | calm |
| 9 | 5 | calm |
| 10 | 5 | calm |
| 11 | 5 | calm |
| 12 | 5 | calm |
| 13 | 5 | calm |
| 14 | 5 | calm |
| 15 | 5 | calm |
| 16 | 5 | calm |
| 17 | 5 | calm |
| 18 | 5 | calm |
| 19 | 5 | calm |
| 20 | 5 | calm |
| 21 | 5 | calm |
| 22 | 5 | calm |
| 23 | 5 | calm |
| 24 | 5 | calm |
| 25 | 5 | calm |
| 26 | 5 | calm |
| 27 | 5 | calm |
| 28 | 5 | calm |
| 29 | 5 | calm |
| 30 | 5 | calm |
| 31 | 5 | calm |
Sunrise & sunset in December
Daylight runs from about 9 h 42 min at the start of December to 9 h 30 min by month's end. The lit band spans sunrise to sunset each day.
Days shrink by about 12 minutes over December. Sunrise moves from 6:47 AM to 7:04 AM, and sunset from 4:26 PM to 4:35 PM.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 9.7 | 9.6 | 9.6 | 9.6 | 9.6 | 9.6 | 9.6 | 9.6 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 | 9.5 |
| Sunrise (AM) | 6:47 | 6:47 | 6:48 | 6:49 | 6:50 | 6:51 | 6:52 | 6:52 | 6:53 | 6:54 | 6:55 | 6:55 | 6:56 | 6:57 | 6:57 | 6:58 | 6:59 | 6:59 | 7:00 | 7:00 | 7:01 | 7:01 | 7:02 | 7:02 | 7:03 | 7:03 | 7:03 | 7:04 | 7:04 | 7:04 | 7:04 |
| Sunset (PM) | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:26 | 4:27 | 4:27 | 4:27 | 4:27 | 4:28 | 4:28 | 4:28 | 4:29 | 4:29 | 4:30 | 4:30 | 4:31 | 4:31 | 4:32 | 4:32 | 4:33 | 4:34 | 4:34 | 4:35 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| 1 | 9.7 | 6:47 | 4:26 |
| 2 | 9.6 | 6:47 | 4:26 |
| 3 | 9.6 | 6:48 | 4:26 |
| 4 | 9.6 | 6:49 | 4:26 |
| 5 | 9.6 | 6:50 | 4:26 |
| 6 | 9.6 | 6:51 | 4:26 |
| 7 | 9.6 | 6:52 | 4:26 |
| 8 | 9.6 | 6:52 | 4:26 |
| 9 | 9.5 | 6:53 | 4:26 |
| 10 | 9.5 | 6:54 | 4:26 |
| 11 | 9.5 | 6:55 | 4:26 |
| 12 | 9.5 | 6:55 | 4:26 |
| 13 | 9.5 | 6:56 | 4:27 |
| 14 | 9.5 | 6:57 | 4:27 |
| 15 | 9.5 | 6:57 | 4:27 |
| 16 | 9.5 | 6:58 | 4:27 |
| 17 | 9.5 | 6:59 | 4:28 |
| 18 | 9.5 | 6:59 | 4:28 |
| 19 | 9.5 | 7:00 | 4:28 |
| 20 | 9.5 | 7:00 | 4:29 |
| 21 | 9.5 | 7:01 | 4:29 |
| 22 | 9.5 | 7:01 | 4:30 |
| 23 | 9.5 | 7:02 | 4:30 |
| 24 | 9.5 | 7:02 | 4:31 |
| 25 | 9.5 | 7:03 | 4:31 |
| 26 | 9.5 | 7:03 | 4:32 |
| 27 | 9.5 | 7:03 | 4:32 |
| 28 | 9.5 | 7:04 | 4:33 |
| 29 | 9.5 | 7:04 | 4:34 |
| 30 | 9.5 | 7:04 | 4:34 |
| 31 | 9.5 | 7:04 | 4:35 |
Solar energy in December
Average shortwave solar energy reaching the ground each day in December, about 2.15 kWh/m² — the year's lowest.
For context, solar energy here swings from a low near 2.15 kWh/m² to a high of 5.65 kWh/m² in May across the year — December's 2.15 kWh/m² sits near the bottom.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.1 | 2.1 | 2.1 | 2.1 | 2.1 | 2.1 | 2.1 | 2.1 | 2.1 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.3 | 2.3 | 2.3 | 2.3 |
| Level | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| 1 | 2.2 | Moderate |
| 2 | 2.2 | Moderate |
| 3 | 2.2 | Moderate |
| 4 | 2.2 | Moderate |
| 5 | 2.2 | Moderate |
| 6 | 2.2 | Moderate |
| 7 | 2.2 | Moderate |
| 8 | 2.1 | Moderate |
| 9 | 2.1 | Moderate |
| 10 | 2.1 | Moderate |
| 11 | 2.1 | Moderate |
| 12 | 2.1 | Moderate |
| 13 | 2.1 | Moderate |
| 14 | 2.1 | Moderate |
| 15 | 2.1 | Moderate |
| 16 | 2.1 | Moderate |
| 17 | 2.2 | Moderate |
| 18 | 2.2 | Moderate |
| 19 | 2.2 | Moderate |
| 20 | 2.2 | Moderate |
| 21 | 2.2 | Moderate |
| 22 | 2.2 | Moderate |
| 23 | 2.2 | Moderate |
| 24 | 2.2 | Moderate |
| 25 | 2.2 | Moderate |
| 26 | 2.2 | Moderate |
| 27 | 2.2 | Moderate |
| 28 | 2.3 | Moderate |
| 29 | 2.3 | Moderate |
| 30 | 2.3 | Moderate |
| 31 | 2.3 | Moderate |
Hazard calendar for Iiyama
In December, Iiyama sits inside its pacific typhoon season. The full year is below, with each hazard's peak months called out.
Iiyama sits in the Pacific typhoon belt; the season peaks July–October.
Is December a good time to visit Iiyama?
Our two travel scores rate December for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).
December is a weaker month for outdoor sightseeing in Iiyama.
What to pack for Iiyama in December
From December's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In December, Iiyama sees daytime highs around 5°C and nights near -3°C. Pack a warm layer and rain gear. Worth having: a heavy coat. About 20 days see rain.
Sea temperature near Iiyama in December
The nearest coast averages about 15°C in December — the other half of the beach question. The full-year curve and swim-comfort zones are below.
The sea at the nearest coast (about 37 km away) is warmest in August at about 27°C and coldest in March near 10°C.
It's comfortable for a long swim from Jun 20 to Nov 1 — about 4.4 months when the water holds above 20°C.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 13 | 11 | 10 | 11 | 15 | 20 | 23 | 27 | 25 | 22 | 19 | 15 |
| Comfort | Bracing | Bracing | Bracing | Bracing | Bracing | Cool | Refreshing | Warm | Warm | Refreshing | Cool | Cool |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 13 | Bracing |
| Feb | 11 | Bracing |
| Mar | 10 | Bracing |
| Apr | 11 | Bracing |
| May | 15 | Bracing |
| Jun | 20 | Cool |
| Jul | 23 | Refreshing |
| Aug | 27 | Warm |
| Sep | 25 | Warm |
| Oct | 22 | Refreshing |
| Nov | 19 | Cool |
| Dec | 15 | Cool |
UV index in Iiyama in December
Clear-sky midday UV in December peaks around 2. The full-year curve, shaded by WHO exposure level, is below.
Under clear skies, the midday UV index in Iiyama peaks around August 13 at about 10 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 at about 2 (moderate).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 3 | 4 | 5 | 7 | 9 | 9 | 10 | 10 | 9 | 6 | 3 | 2 |
| Level | Moderate | Moderate | High | Very high | Very high | Very high | Very high | Extreme | Very high | High | Moderate | Moderate |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 3 | Moderate |
| Feb | 4 | Moderate |
| Mar | 5 | High |
| Apr | 7 | Very high |
| May | 9 | Very high |
| Jun | 9 | Very high |
| Jul | 10 | Very high |
| Aug | 10 | Extreme |
| Sep | 9 | Very high |
| Oct | 6 | High |
| Nov | 3 | Moderate |
| Dec | 2 | Moderate |
Air quality in Iiyama in December
Average fine-particle pollution (PM2.5) through the year — so you can see where December falls, not just the annual average.
Air quality in Iiyama is worst in April — around 21 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (December, 10 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 11 | 14 | 20 | 21 | 20 | 18 | 15 | 13 | 12 | 11 | 11 | 10 |
| Level | Good | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Good | Good | Good |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 11 | Good |
| Feb | 14 | Moderate |
| Mar | 20 | Moderate |
| Apr | 21 | Moderate |
| May | 20 | Moderate |
| Jun | 18 | Moderate |
| Jul | 15 | Moderate |
| Aug | 13 | Moderate |
| Sep | 12 | Good |
| Oct | 11 | Good |
| Nov | 11 | Good |
| Dec | 10 | Good |
Where is Iiyama?
Iiyama sits at 36.9°N, 138.4°E, 311 m above sea level, in Japan. The nearest listed city is Nakano, 11 km away.
Topography around Iiyama
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Iiyama.
Within 3 km, the terrain around Iiyama has significant variations in elevation — a maximum elevation change of 486 m around an average of 382 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 1,870 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,978 m.
The land around Iiyama is covered by trees (43%) and cropland (38%) within 3 km, trees (79%) within 16 km, and trees (70%) within 80 km.
Japan travel facts
- Travel advisory
- Level 1
- Exercise Normal Precautions
- Power plugs
- Type A / B
- 100 V · 50 / 60 Hz
- Prices
- ≈ 65% of US
- price level, 2025
- GDP per capita
- $35,951
- 2025
- Happiness
- 6.1 / 10
- World Happiness, 2025
- Safe drinking water
- 99%
- of population, 2024
- Homicide rate
- 0.2
- per 100k, 2023
- Road deaths
- 3.6
- per 100k/yr, 2019
- Income group
- High
- World Bank
- English
- Very low
- EF EPI 446
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Iiyama (36.85°, 138.3667°, elevation 311 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).