Climate and average weather in Iwamizawa
In Iwamizawa, the summers are warm, showery, and mostly cloudy and the winters are very cold, snowy, and partly cloudy.
Over the course of the year, the temperature in Iwamizawa typically varies from -10°C to 24°C, and is rarely below -16°C or above 29°C. August is the hottest month of the year, while January is the coldest.
Based on the travel score, the best time of year to visit Iwamizawa for warm-weather activities is from late May to early October.
- Hottest
- Aug
- 24°
- Coldest
- Jan
- -10°
- Wettest
- Aug
- 161 mm
- Driest
- Feb
- 42 mm
- Rain / yr
- 1011 mm
- 150 wet days
- Daylight
- 8.8–15.2 h
- shortest–longest
- Elevation
- 17 m
- 43.2°N
- Clearest
- Oct
- 58% cloud
Iwamizawa is city in Hokkaido, Japan.
- Density
- 177/km²
- people per km²
- Founded
- 1943
Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.
Iwamizawa weather by month, at a glance
The whole year in one picture — sky, rain, humidity, temperature and travel score. Click any band to jump to its full chart.
Each stripe is one measure across the whole year, stacked so a single day reads top to bottom. The sky band runs overcast grey on top down to clear blue at the base — more blue means sunnier — followed by the rainfall curve, the humidity band, a temperature strip that tints each stretch of the year by how warm its average high is, and the travel-score line at the foot. Scan straight down any date to read that day across every measure at once; the score climbs highest around late May to early October.
Temperature through the year
Daily average highs and lows in Iwamizawa, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
The hot season lasts 4.1 months, from May 30 to October 1, with daily high temperatures above 18°C. The hottest month of the year in Iwamizawa is August, with an average high of 24°C and low of 18°C.
The cool season lasts 3.4 months, from December 2 to March 15, with daily high temperatures below 3°C. The coldest month of the year in Iwamizawa is January, with an average low of -10°C and high of -3°C.
Days typically run about 8°C warmer than nights year-round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | -3 | -1 | 3 | 11 | 16 | 20 | 23 | 24 | 21 | 15 | 7 | 0 |
| Avg low (°C) | -10 | -9 | -5 | 2 | 8 | 12 | 17 | 18 | 13 | 6 | 0 | -7 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| Jan | -3 | -10 |
| Feb | -1 | -9 |
| Mar | 3 | -5 |
| Apr | 11 | 2 |
| May | 16 | 8 |
| Jun | 20 | 12 |
| Jul | 23 | 17 |
| Aug | 24 | 18 |
| Sep | 21 | 13 |
| Oct | 15 | 6 |
| Nov | 7 | 0 |
| Dec | 0 | -7 |
How hot and cold Iwamizawa really feels
The felt-temperature range through the year — heat index on the day's high (summer humidity), wind chill on the night's low (winter wind). The dashed lines are the plain thermometer; the gap is how much hotter or colder it really feels.
On the coldest nights, wind chill pulls the feels-like down to about -16°C (around January 26), with roughly 169 freezing days a year (feels-like at or below 0°C) — 98 of them bitterly cold — worst in January.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels-like high (°C) | -3 | -2 | 3 | 11 | 16 | 20 | 23 | 24 | 21 | 15 | 7 | 0 |
| Air high (°C) | -3 | -1 | 3 | 11 | 16 | 20 | 23 | 24 | 21 | 15 | 7 | 0 |
| Feels-like low (°C) | -15 | -14 | -10 | -2 | 6 | 12 | 17 | 18 | 13 | 4 | -4 | -11 |
| Air low (°C) | -10 | -9 | -5 | 2 | 8 | 12 | 17 | 18 | 13 | 6 | 0 | -7 |
| Feels-like high (°C) | Air high (°C) | Feels-like low (°C) | Air low (°C) | |
|---|---|---|---|---|
| Jan | -3 | -3 | -15 | -10 |
| Feb | -2 | -1 | -14 | -9 |
| Mar | 3 | 3 | -10 | -5 |
| Apr | 11 | 11 | -2 | 2 |
| May | 16 | 16 | 6 | 8 |
| Jun | 20 | 20 | 12 | 12 |
| Jul | 23 | 23 | 17 | 17 |
| Aug | 24 | 24 | 18 | 18 |
| Sep | 21 | 21 | 13 | 13 |
| Oct | 15 | 15 | 4 | 6 |
| Nov | 7 | 7 | -4 | 0 |
| Dec | 0 | 0 | -11 | -7 |
Average hourly temperature in Iwamizawa
A compact picture of the whole year, hour by hour: each column is a day, each row an hour, and the color is the modeled average temperature. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
Read left to right for the day of the year and top to bottom for the hour of the day; the color is the modeled temperature, cool blues through to hot reds on the same scale as the other charts. A vertical slice is a single day's swing — coolest just before dawn, warmest in the mid-afternoon — while a horizontal slice follows one hour across the seasons. The darker overlay marks night and the lighter one the twilight around sunrise and sunset. Colors run warmest on August afternoons, near 24°C, and coldest before dawn in January, near -10°C.
Iwamizawa weather by month
Every month at a glance. Click a month for its detailed page.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | -3° / -10° | 49 | 12.7 | 18.1 | 9.2 | 0.0 |
| Feb | -2° / -9° | 42 | 10.7 | 14.9 | 10.2 | 0.0 |
| Mar | 3° / -5° | 57 | 11.6 | 10.5 | 11.6 | 0.1 |
| Apr | 11° / 2° | 67 | 11.8 | 3.3 | 13.1 | 2.5 |
| May | 16° / 8° | 84 | 11.4 | 0.1 | 14.4 | 4.9 |
| Jun | 20° / 12° | 64 | 9.6 | 0 | 15.1 | 6.1 |
| Jul | 23° / 17° | 113 | 11.6 | 0 | 14.9 | 6.4 |
| Aug | 24° / 18° | 161 | 12.5 | 0 | 13.8 | 6.3 |
| Sep | 21° / 13° | 126 | 13.2 | 0 | 12.3 | 5.9 |
| Oct | 15° / 6° | 92 | 13.6 | 0.3 | 10.8 | 4.1 |
| Nov | 7° / 0° | 87 | 16.1 | 8.4 | 9.5 | 0.9 |
| Dec | 0° / -7° | 69 | 15.3 | 18.1 | 8.9 | 0.0 |
Chance of rain
How likely it is to rain on a typical day, and how that shifts across the wetter and drier seasons.
Iwamizawa gets about 1011 mm of precipitation a year. On a typical day the chance of rain is often wet, but that rises and falls sharply with the seasons.
The wetter season lasts 4.6 months, from around Aug 27 to Jan 13, peaking in November at about 55% chance on a given day. The drier stretch runs the rest of the year, bottoming out around Jun 21.
August is the wettest month by volume, with 161 mm over about 13 wet days; February is the driest, with 42 mm. Some of the cold-season precipitation falls as snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain on a day (%) | 41 | 39 | 38 | 39 | 37 | 32 | 36 | 41 | 44 | 44 | 53 | 49 |
| Rain days | 13 | 11 | 12 | 12 | 11 | 10 | 12 | 13 | 13 | 14 | 16 | 15 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 41 | 13 |
| Feb | 39 | 11 |
| Mar | 38 | 12 |
| Apr | 39 | 12 |
| May | 37 | 11 |
| Jun | 32 | 10 |
| Jul | 36 | 12 |
| Aug | 41 | 13 |
| Sep | 44 | 13 |
| Oct | 44 | 14 |
| Nov | 53 | 16 |
| Dec | 49 | 15 |
Monthly rainfall
Over a full year, Iwamizawa collects about 1011 mm of rain across 150 wet days — roughly 84 mm in an average month.
It doesn’t fall evenly. August is the wettest month with 161 mm, while February is the driest at just 42 mm. The three wettest months alone bring about 40% of the year’s total, and some of the cold-season precipitation falls as snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rainfall (mm) | 49 | 42 | 57 | 67 | 84 | 64 | 113 | 161 | 126 | 92 | 87 | 69 |
| Rain days | 13 | 11 | 12 | 12 | 11 | 10 | 12 | 13 | 13 | 14 | 16 | 15 |
| Snow days | 18 | 15 | 11 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 8 | 18 |
| Rainfall (mm) | Rain days | Snow days | |
|---|---|---|---|
| Jan | 49 | 13 | 18 |
| Feb | 42 | 11 | 15 |
| Mar | 57 | 12 | 11 |
| Apr | 67 | 12 | 3 |
| May | 84 | 11 | 0 |
| Jun | 64 | 10 | 0 |
| Jul | 113 | 12 | 0 |
| Aug | 161 | 13 | 0 |
| Sep | 126 | 13 | 0 |
| Oct | 92 | 14 | 0 |
| Nov | 87 | 16 | 8 |
| Dec | 69 | 15 | 18 |
Snow in Iwamizawa
Average snowy days through the year, the snow-season span, and estimated snowfall — for ski trips and the perennial 'will there be snow at Christmas?' question.
Iwamizawa averages about 74 snowy days a year. Snow season runs roughly Oct 21 to May 4 — about 6.4 months.
January is snowiest, with roughly 18 days of snow and an estimated 58 cm of snowfall. Over the year that adds up to an estimated 259 cm of snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Snow days | 18 | 15 | 11 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 8 | 18 |
| Snowfall (cm) | 58 | 57 | 37 | 11 | 1 | 0 | 0 | 0 | 0 | 2 | 29 | 64 |
| Snow days | Snowfall (cm) | |
|---|---|---|
| Jan | 18 | 58 |
| Feb | 15 | 57 |
| Mar | 11 | 37 |
| Apr | 3 | 11 |
| May | 0 | 1 |
| Jun | 0 | 0 |
| Jul | 0 | 0 |
| Aug | 0 | 0 |
| Sep | 0 | 0 |
| Oct | 0 | 2 |
| Nov | 8 | 29 |
| Dec | 18 | 64 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In Iwamizawa, the average share of the sky covered by clouds shows moderate seasonal variation over the course of the year.
The clearer part of the year begins around September 8 and lasts for 2.4 months, ending around November 20. The clearest month is October, when the sky is clear, mostly clear, or partly cloudy 52% of the time on average.
The cloudier part of the year begins around November 21 and lasts for 3.5 months, ending around March 6. The cloudiest month is July, when it is overcast or mostly cloudy 71% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 30 | 31 | 43 | 46 | 40 | 36 | 29 | 32 | 42 | 52 | 41 | 34 |
| Cloudier (%) | 70 | 69 | 57 | 54 | 60 | 64 | 71 | 68 | 58 | 48 | 59 | 66 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 30 | 70 |
| Feb | 31 | 69 |
| Mar | 43 | 57 |
| Apr | 46 | 54 |
| May | 40 | 60 |
| Jun | 36 | 64 |
| Jul | 29 | 71 |
| Aug | 32 | 68 |
| Sep | 42 | 58 |
| Oct | 52 | 48 |
| Nov | 41 | 59 |
| Dec | 34 | 66 |
Daylight, sunrise and sunset
Hours of daylight through the year, with sunrise and sunset times.
The gold band is daylight — sunrise runs along its lower edge, sunset along the upper — so it widens toward summer and pinches toward winter, with night the dark area above and below. The longest day, around June 13, brings about 15 h 12 min of light; the shortest, around December 13, only 8 h 48 min — a swing of roughly 6 h 24 min.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 9.2 | 10.2 | 11.6 | 13.1 | 14.4 | 15.1 | 14.9 | 13.8 | 12.3 | 10.8 | 9.5 | 8.9 |
| Sunrise (AM) | 7:08 | 6:40 | 5:54 | 4:58 | 4:15 | 3:58 | 4:12 | 4:43 | 5:19 | 5:54 | 6:34 | 7:05 |
| Sunset (PM) | 4:16 | 4:55 | 5:32 | 6:09 | 6:43 | 7:09 | 7:06 | 6:31 | 5:36 | 4:42 | 4:02 | 3:54 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 9.2 | 7:08 | 4:16 |
| Feb | 10.2 | 6:40 | 4:55 |
| Mar | 11.6 | 5:54 | 5:32 |
| Apr | 13.1 | 4:58 | 6:09 |
| May | 14.4 | 4:15 | 6:43 |
| Jun | 15.1 | 3:58 | 7:09 |
| Jul | 14.9 | 4:12 | 7:06 |
| Aug | 13.8 | 4:43 | 6:31 |
| Sep | 12.3 | 5:19 | 5:36 |
| Oct | 10.8 | 5:54 | 4:42 |
| Nov | 9.5 | 6:34 | 4:02 |
| Dec | 8.9 | 7:05 | 3:54 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
Iwamizawa averages about 6 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 3 and 10 days.
The sunnier stretch runs 3.3 months, from around Mar 14 to Jun 22. The sunniest month is April, with roughly 9 sunny days (mixed).
The greyest month is December, down near 3 sunny days — about 68% fewer than the April peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 3 | 3 | 7 | 9 | 9 | 6 | 5 | 5 | 8 | 9 | 5 | 3 |
| Sky | Gloomy | Gloomy | Gloomy | Mixed | Mixed | Gloomy | Gloomy | Gloomy | Gloomy | Mixed | Gloomy | Gloomy |
| Sunny days | Sky | |
|---|---|---|
| Jan | 3 | Gloomy |
| Feb | 3 | Gloomy |
| Mar | 7 | Gloomy |
| Apr | 9 | Mixed |
| May | 9 | Mixed |
| Jun | 6 | Gloomy |
| Jul | 5 | Gloomy |
| Aug | 5 | Gloomy |
| Sep | 8 | Gloomy |
| Oct | 9 | Mixed |
| Nov | 5 | Gloomy |
| Dec | 3 | Gloomy |
Humidity comfort
Share of days at each humidity comfort level, based on the dew point — the measure that tracks how muggy it actually feels.
Humidity comfort is graded by the dew point — the temperature at which the air would be fully saturated — because it tracks how muggy it actually feels far better than relative humidity does. A low dew point feels dry and crisp; a high one feels sticky and oppressive no matter the reading on a humidity gauge.
In Iwamizawa, how humid it feels changes dramatically over the year.
The more humid part of the year lasts 2.9 months, from around June 24 to September 20. The muggiest month is August, when the air feels humid, muggy or worse about 77% of the time.
The most comfortable stretch runs from around September 21 to June 23, and May is the most comfortable month — the air is dry or comfortable 100% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 100 | 100 | 100 | 100 | 98 | 61 | 12 | 6 | 47 | 95 | 100 | 100 |
| Comfortable (%) | 0 | 0 | 0 | 0 | 2 | 30 | 29 | 17 | 26 | 4 | 0 | 0 |
| Humid (%) | 0 | 0 | 0 | 0 | 0 | 8 | 35 | 37 | 17 | 0 | 0 | 0 |
| Muggy (%) | 0 | 0 | 0 | 0 | 0 | 1 | 20 | 30 | 9 | 0 | 0 | 0 |
| Oppressive (%) | 0 | 0 | 0 | 0 | 0 | 0 | 4 | 10 | 2 | 0 | 0 | 0 |
| Dry (%) | Comfortable (%) | Humid (%) | Muggy (%) | Oppressive (%) | |
|---|---|---|---|---|---|
| Jan | 100 | 0 | 0 | 0 | 0 |
| Feb | 100 | 0 | 0 | 0 | 0 |
| Mar | 100 | 0 | 0 | 0 | 0 |
| Apr | 100 | 0 | 0 | 0 | 0 |
| May | 98 | 2 | 0 | 0 | 0 |
| Jun | 61 | 30 | 8 | 1 | 0 |
| Jul | 12 | 29 | 35 | 20 | 4 |
| Aug | 6 | 17 | 37 | 30 | 10 |
| Sep | 47 | 26 | 17 | 9 | 2 |
| Oct | 95 | 4 | 0 | 0 | 0 |
| Nov | 100 | 0 | 0 | 0 | 0 |
| Dec | 100 | 0 | 0 | 0 | 0 |
Wind
Average wind speed through the year, banded into plain-language speed zones so a number reads as 'breezy' or 'calm' without knowing the scale.
This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.
Wind in Iwamizawa is steady company: average speeds sit near 11 km/h — calm — in every month of the year, with no meaningful windy or calm season.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (km/h) | 10 | 11 | 12 | 12 | 12 | 10 | 10 | 10 | 10 | 11 | 11 | 11 |
| Feels | calm | calm | calm | light breeze | calm | calm | calm | calm | calm | calm | calm | calm |
| Wind speed (km/h) | Feels | |
|---|---|---|
| Jan | 10 | calm |
| Feb | 11 | calm |
| Mar | 12 | calm |
| Apr | 12 | light breeze |
| May | 12 | calm |
| Jun | 10 | calm |
| Jul | 10 | calm |
| Aug | 10 | calm |
| Sep | 10 | calm |
| Oct | 11 | calm |
| Nov | 11 | calm |
| Dec | 11 | calm |
Hazard calendar for Iwamizawa
When the seasonal hazards worth planning around — the rainy season, tropical-cyclone risk and dust haze — are active through the year.
Iwamizawa sits in the Pacific typhoon belt; the season peaks July–October.
Best time to visit Iwamizawa
To characterize how pleasant the weather is in Iwamizawa throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around late September, Iwamizawa is still near the tail of its best-weather window — great conditions with the peak-season crowds already thinning.
Inferred from the travel-score curve; month-by-month visitor numbers are a planned addition.
The travel score favors clear, rainless days with daytime highs between 18°C and 28°C. Based on this score, the best time of year to visit Iwamizawa for general outdoor tourist activities is from late May to early October, with a peak score in the third week of July.
The travel score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Travel score (0–10) | 0.0 | 0.0 | 0.1 | 2.4 | 4.9 | 6.1 | 6.4 | 6.3 | 5.9 | 4.1 | 1.0 | 0.0 |
| Rating | poor | poor | poor | poor | fair | good | good | good | good | fair | poor | poor |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 0.0 | poor |
| Feb | 0.0 | poor |
| Mar | 0.1 | poor |
| Apr | 2.4 | poor |
| May | 4.9 | fair |
| Jun | 6.1 | good |
| Jul | 6.4 | good |
| Aug | 6.3 | good |
| Sep | 5.9 | good |
| Oct | 4.1 | fair |
| Nov | 1.0 | poor |
| Dec | 0.0 | poor |
The beach/pool score favors clear, rainless days with daytime highs between 24°C and 34°C. Based on this score, the best time of year to visit Iwamizawa for hot-weather activities is from early July to early September, with a peak score in the first week of August.
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
What to pack for Iwamizawa, by month
Month by month, what's worth putting in the bag — from the temperature range, rain chance, sun and wind. Tap a month for a quick packing note.
For a warm-season trip around August (highs near 24°C), the essentials are light clothes and rain gear. In the cold season around January (highs near -3°C), pack a warm layer, a heavy coat and rain gear.
In August, Iwamizawa sees daytime highs around 24°C and nights near 18°C. Worth packing: light clothes and rain gear. About 13 days see rain.
Sea temperature near Iwamizawa
Average ocean temperature at the nearest coast, month by month, banded into swim-comfort zones — the other half of the beach question.
The sea at the nearest coast (about 37 km away) is warmest in August at about 22°C and coldest in February near 5°C.
It's comfortable for a long swim from Jul 31 to Sep 22 — about 1.8 months when the water holds above 20°C.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 7 | 5 | 5 | 7 | 10 | 14 | 19 | 22 | 21 | 17 | 13 | 9 |
| Comfort | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Cool | Refreshing | Refreshing | Cool | Bracing | Bracing |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 7 | Bracing |
| Feb | 5 | Bracing |
| Mar | 5 | Bracing |
| Apr | 7 | Bracing |
| May | 10 | Bracing |
| Jun | 14 | Bracing |
| Jul | 19 | Cool |
| Aug | 22 | Refreshing |
| Sep | 21 | Refreshing |
| Oct | 17 | Cool |
| Nov | 13 | Bracing |
| Dec | 9 | Bracing |
UV index (midday) in Iwamizawa by month
Clear-sky midday UV index through the year, shaded by the WHO exposure levels — how much sun protection each month calls for.
Under clear skies, the midday UV index in Iwamizawa peaks around August 18 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 19 at about 1 (low).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 1 | 3 | 3 | 6 | 7 | 7 | 5 | 8 | 6 | 4 | 2 | 1 |
| Level | Low | Moderate | Moderate | High | Very high | High | Moderate | Very high | High | Moderate | Low | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 1 | Low |
| Feb | 3 | Moderate |
| Mar | 3 | Moderate |
| Apr | 6 | High |
| May | 7 | Very high |
| Jun | 7 | High |
| Jul | 5 | Moderate |
| Aug | 8 | Very high |
| Sep | 6 | High |
| Oct | 4 | Moderate |
| Nov | 2 | Low |
| Dec | 1 | Low |
Average hourly UV index in Iwamizawa
Modeled clear-sky UV for every hour of every day — when in the day sun protection actually matters.
The whole year hour by hour: each column is a day, each row an hour, and the color is the modeled clear-sky UV index — the midday peak scaled down as the sun sits lower in the sky. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
UV falls off far faster than brightness as the sun drops, so even in August the burn window is concentrated in the middle of the day: about 7.5 hours a day reach index 3 (protection recommended), and 4.5 hours reach 6 or more. Mornings and late afternoons stay comparatively gentle year round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV ≥ 3 (h/day) | 0 | 0 | 2.5 | 6 | 7.5 | 7.5 | 6.5 | 7.5 | 6 | 3 | 0 | 0 |
| UV ≥ 6 (h/day) | 0 | 0 | 0 | 0 | 3.5 | 2.5 | 0 | 4.5 | 1 | 0 | 0 | 0 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 0 | 0 |
| Feb | 0 | 0 |
| Mar | 2.5 | 0 |
| Apr | 6 | 0 |
| May | 7.5 | 3.5 |
| Jun | 7.5 | 2.5 |
| Jul | 6.5 | 0 |
| Aug | 7.5 | 4.5 |
| Sep | 6 | 1 |
| Oct | 3 | 0 |
| Nov | 0 | 0 |
| Dec | 0 | 0 |
Air quality in Iwamizawa by month
Average fine-particle pollution (PM2.5) through the year — so you can see which months the air is worst, not just the yearly average.
Air quality in Iwamizawa is worst in April — around 21 µg/m³ PM2.5 (moderate), about 2.3× the cleanest month (December, 9 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 | 15 | 20 | 21 | 19 | 14 | 13 | 11 | 11 | 12 | 10 | 9 |
| Level | Good | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Good | Good | Good | Good |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 11 | Good |
| Feb | 15 | Moderate |
| Mar | 20 | Moderate |
| Apr | 21 | Moderate |
| May | 19 | Moderate |
| Jun | 14 | Moderate |
| Jul | 13 | Moderate |
| Aug | 11 | Good |
| Sep | 11 | Good |
| Oct | 12 | Good |
| Nov | 10 | Good |
| Dec | 9 | Good |
Growing season
The growing season in Iwamizawa typically lasts about 222 days, from around April 8 to November 15 — the span where a frost-free day is more likely than not. It is reliably frost-free from April 27 to October 28.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 1 | 1 | 11 | 67 | 99 | 100 | 100 | 100 | 100 | 96 | 51 | 6 |
| Frost nights | 31 | 28 | 31 | 25 | 0 | 0 | 0 | 0 | 0 | 2 | 30 | 31 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 1 | 31 |
| Feb | 1 | 28 |
| Mar | 11 | 31 |
| Apr | 67 | 25 |
| May | 99 | 0 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 100 | 0 |
| Oct | 96 | 2 |
| Nov | 51 | 30 |
| Dec | 6 | 31 |
Growing degree days
Growing degree days tally heat above 10°C: each day adds however many degrees its average temperature runs over that threshold, and cold days add nothing. Iwamizawa banks about 1,140 degree days a year, and the running total — which growers use to time plantings and predict maturity — climbs fastest around August.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Growing degree days (°C·days) | 0 | 0 | 0 | 0 | 61 | 182 | 308 | 343 | 212 | 34 | 0 | 0 |
| Growing degree days (°C·days) | |
|---|---|
| Jan | 0 |
| Feb | 0 |
| Mar | 0 |
| Apr | 0 |
| May | 61 |
| Jun | 182 |
| Jul | 308 |
| Aug | 343 |
| Sep | 212 |
| Oct | 34 |
| Nov | 0 |
| Dec | 0 |
Solar energy
Average daily shortwave solar energy reaching the ground, banded into brightness zones so the number means something at a glance.
Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.
Iwamizawa receives about 3.7 kWh/m² a day of solar energy on average — moderate — with a clear seasonal swing between 1.6 and 5.5 kWh/m².
The brighter stretch of the year lasts 6.5 months, from around Mar 1 to Sep 13. The brightest month is May, averaging about 5.4 kWh/m² (bright).
The dimmest month is December, down near 1.6 kWh/m² — roughly 69% less than the May peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 2.1 | 3.1 | 4.4 | 5.0 | 5.4 | 5.3 | 4.8 | 4.3 | 3.6 | 2.8 | 1.8 | 1.6 |
| Level | Moderate | Moderate | Bright | Bright | Bright | Bright | Bright | Bright | Moderate | Moderate | Dim | Dim |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 2.1 | Moderate |
| Feb | 3.1 | Moderate |
| Mar | 4.4 | Bright |
| Apr | 5.0 | Bright |
| May | 5.4 | Bright |
| Jun | 5.3 | Bright |
| Jul | 4.8 | Bright |
| Aug | 4.3 | Bright |
| Sep | 3.6 | Moderate |
| Oct | 2.8 | Moderate |
| Nov | 1.8 | Dim |
| Dec | 1.6 | Dim |
Where is Iwamizawa?
Iwamizawa sits at 43.2°N, 141.8°E, 17 m above sea level, in Japan. The nearest listed city is Bibai, 16 km away.
Topography around Iwamizawa
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Iwamizawa.
Within 3 km, the terrain around Iwamizawa has only modest variations in elevation — a maximum elevation change of 101 m around an average of 24 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 559 m; within 80 km, very significant variations in elevation — a maximum elevation change of 2,032 m.
The land around Iwamizawa is covered by artificial surfaces (43%) and cropland (35%) within 3 km, cropland (54%) and trees (33%) within 16 km, and trees (64%) 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 Iwamizawa (43.2003°, 141.7597°, elevation 17 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).