Climate and average weather in Mariehamn
In Mariehamn, the summers are mild, showery, and partly cloudy and the winters are very cold, windy, snowy, and mostly cloudy.
Over the course of the year, the temperature in Mariehamn typically varies from -2°C to 18°C, and is rarely below -9°C or above 21°C. August is the hottest month of the year, while February is the coldest.
Based on the travel score, the best time of year to visit Mariehamn for warm-weather activities is from early July to late August.
- Hottest
- Aug
- 18°
- Coldest
- Feb
- -2°
- Wettest
- Oct
- 62 mm
- Driest
- Mar
- 27 mm
- Rain / yr
- 545 mm
- 111 wet days
- Daylight
- 5.5–18.5 h
- shortest–longest
- Elevation
- 11 m
- 60.1°N
- Clearest
- Jul
- 49% cloud
Mariehamn 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 early July to late August.
Temperature through the year
Daily average highs and lows in Mariehamn, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
The hot season lasts 2.9 months, from June 22 to September 18, with daily high temperatures above 14°C. The hottest month of the year in Mariehamn is August, with an average high of 18°C and low of 16°C.
The cool season lasts 3.9 months, from December 13 to April 10, with daily high temperatures below 4°C. The coldest month of the year in Mariehamn is February, with an average low of -2°C and high of 0°C.
Days typically run about 2°C warmer than nights year-round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 2 | 0 | 1 | 4 | 8 | 13 | 17 | 18 | 14 | 9 | 6 | 3 |
| Avg low (°C) | -1 | -2 | -1 | 2 | 6 | 11 | 15 | 16 | 13 | 8 | 4 | 1 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| Jan | 2 | -1 |
| Feb | 0 | -2 |
| Mar | 1 | -1 |
| Apr | 4 | 2 |
| May | 8 | 6 |
| Jun | 13 | 11 |
| Jul | 17 | 15 |
| Aug | 18 | 16 |
| Sep | 14 | 13 |
| Oct | 9 | 8 |
| Nov | 6 | 4 |
| Dec | 3 | 1 |
How hot and cold Mariehamn 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 -9°C (around February 18), with roughly 176 freezing days a year (feels-like at or below 0°C), worst in February.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels-like high (°C) | 1 | 0 | 1 | 4 | 8 | 13 | 17 | 17 | 14 | 9 | 6 | 3 |
| Air high (°C) | 2 | 0 | 1 | 4 | 8 | 13 | 17 | 18 | 14 | 9 | 6 | 3 |
| Feels-like low (°C) | -7 | -9 | -7 | -3 | 3 | 10 | 15 | 16 | 12 | 4 | -1 | -5 |
| Air low (°C) | -1 | -2 | -1 | 2 | 6 | 11 | 15 | 16 | 13 | 8 | 4 | 1 |
| Feels-like high (°C) | Air high (°C) | Feels-like low (°C) | Air low (°C) | |
|---|---|---|---|---|
| Jan | 1 | 2 | -7 | -1 |
| Feb | 0 | 0 | -9 | -2 |
| Mar | 1 | 1 | -7 | -1 |
| Apr | 4 | 4 | -3 | 2 |
| May | 8 | 8 | 3 | 6 |
| Jun | 13 | 13 | 10 | 11 |
| Jul | 17 | 17 | 15 | 15 |
| Aug | 17 | 18 | 16 | 16 |
| Sep | 14 | 14 | 12 | 13 |
| Oct | 9 | 9 | 4 | 8 |
| Nov | 6 | 6 | -1 | 4 |
| Dec | 3 | 3 | -5 | 1 |
Average hourly temperature in Mariehamn
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 18°C, and coldest before dawn in February, near -2°C.
Mariehamn 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 | 2° / -1° | 43 | 10.5 | 8 | 6.4 | 0.0 |
| Feb | 0° / -2° | 29 | 7.7 | 6.5 | 8.6 | 0.0 |
| Mar | 1° / -1° | 27 | 7.1 | 5.1 | 11.3 | 0.0 |
| Apr | 4° / 2° | 29 | 6.9 | 1.7 | 14.2 | 0.0 |
| May | 8° / 6° | 33 | 6.6 | 0.2 | 16.8 | 1.6 |
| Jun | 13° / 11° | 49 | 7.5 | 0 | 18.4 | 3.8 |
| Jul | 17° / 15° | 48 | 7.6 | 0 | 17.7 | 5.9 |
| Aug | 18° / 16° | 55 | 10.2 | 0 | 15.4 | 5.8 |
| Sep | 14° / 13° | 54 | 9.2 | 0 | 12.6 | 4.1 |
| Oct | 9° / 8° | 62 | 11.8 | 0.4 | 9.8 | 1.9 |
| Nov | 6° / 4° | 60 | 13 | 2.9 | 7.1 | 0.4 |
| Dec | 3° / 1° | 56 | 13 | 6.1 | 5.6 | 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.
Mariehamn gets about 545 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 4.2 months, from around Sep 28 to Feb 3, peaking in November at about 47% chance on a given day. The drier stretch runs the rest of the year, bottoming out around May 16.
October is the wettest month by volume, with 62 mm over about 12 wet days; March is the driest, with 27 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 (%) | 34 | 28 | 23 | 23 | 21 | 25 | 25 | 32 | 32 | 37 | 43 | 42 |
| Rain days | 11 | 8 | 7 | 7 | 7 | 8 | 8 | 10 | 9 | 12 | 13 | 13 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 34 | 11 |
| Feb | 28 | 8 |
| Mar | 23 | 7 |
| Apr | 23 | 7 |
| May | 21 | 7 |
| Jun | 25 | 8 |
| Jul | 25 | 8 |
| Aug | 32 | 10 |
| Sep | 32 | 9 |
| Oct | 37 | 12 |
| Nov | 43 | 13 |
| Dec | 42 | 13 |
Monthly rainfall
Over a full year, Mariehamn collects about 545 mm of rain across 111 wet days — roughly 45 mm in an average month.
It doesn’t fall evenly. October is the wettest month with 62 mm, while March is the driest at just 27 mm. The three wettest months alone bring about 33% 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) | 43 | 29 | 27 | 29 | 33 | 49 | 48 | 55 | 54 | 62 | 60 | 56 |
| Rain days | 11 | 8 | 7 | 7 | 7 | 8 | 8 | 10 | 9 | 12 | 13 | 13 |
| Snow days | 8 | 7 | 5 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 6 |
| Rainfall (mm) | Rain days | Snow days | |
|---|---|---|---|
| Jan | 43 | 11 | 8 |
| Feb | 29 | 8 | 7 |
| Mar | 27 | 7 | 5 |
| Apr | 29 | 7 | 2 |
| May | 33 | 7 | 0 |
| Jun | 49 | 8 | 0 |
| Jul | 48 | 8 | 0 |
| Aug | 55 | 10 | 0 |
| Sep | 54 | 9 | 0 |
| Oct | 62 | 12 | 0 |
| Nov | 60 | 13 | 3 |
| Dec | 56 | 13 | 6 |
Snow in Mariehamn
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.
Mariehamn averages about 31 snowy days a year. Snow season runs roughly Oct 21 to May 3 — about 6.4 months.
January is snowiest, with roughly 8 days of snow and an estimated 24 cm of snowfall. Over the year that adds up to an estimated 99 cm of snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Snow days | 8 | 7 | 5 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 6 |
| Snowfall (cm) | 24 | 22 | 17 | 4 | 0 | 0 | 0 | 0 | 0 | 1 | 9 | 22 |
| Snow days | Snowfall (cm) | |
|---|---|---|
| Jan | 8 | 24 |
| Feb | 7 | 22 |
| Mar | 5 | 17 |
| Apr | 2 | 4 |
| May | 0 | 0 |
| Jun | 0 | 0 |
| Jul | 0 | 0 |
| Aug | 0 | 0 |
| Sep | 0 | 0 |
| Oct | 0 | 1 |
| Nov | 3 | 9 |
| Dec | 6 | 22 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In Mariehamn, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.
The clearer part of the year begins around March 18 and lasts for 6.6 months, ending around October 3. The clearest month is July, when the sky is clear, mostly clear, or partly cloudy 62% of the time on average.
The cloudier part of the year begins around October 4 and lasts for 5.4 months, ending around March 17. The cloudiest month is November, when it is overcast or mostly cloudy 78% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 23 | 25 | 38 | 49 | 57 | 55 | 62 | 54 | 47 | 33 | 22 | 24 |
| Cloudier (%) | 77 | 75 | 62 | 51 | 43 | 45 | 38 | 46 | 53 | 67 | 78 | 76 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 23 | 77 |
| Feb | 25 | 75 |
| Mar | 38 | 62 |
| Apr | 49 | 51 |
| May | 57 | 43 |
| Jun | 55 | 45 |
| Jul | 62 | 38 |
| Aug | 54 | 46 |
| Sep | 47 | 53 |
| Oct | 33 | 67 |
| Nov | 22 | 78 |
| Dec | 24 | 76 |
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 16, brings about 18 h 30 min of light; the shortest, around December 15, only 5 h 30 min — a swing of roughly 13 hours.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 6.4 | 8.6 | 11.3 | 14.2 | 16.8 | 18.4 | 17.7 | 15.4 | 12.6 | 9.8 | 7.1 | 5.6 |
| Sunrise (AM) | 9:40 | 8:35 | 7:10 | 5:34 | 4:12 | 3:27 | 3:52 | 5:03 | 6:18 | 7:33 | 8:53 | 9:51 |
| Sunset (PM) | 3:59 | 5:15 | 6:30 | 7:47 | 9:01 | 9:54 | 9:39 | 8:26 | 6:51 | 5:18 | 3:58 | 3:22 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 6.4 | 9:40 | 3:59 |
| Feb | 8.6 | 8:35 | 5:15 |
| Mar | 11.3 | 7:10 | 6:30 |
| Apr | 14.2 | 5:34 | 7:47 |
| May | 16.8 | 4:12 | 9:01 |
| Jun | 18.4 | 3:27 | 9:54 |
| Jul | 17.7 | 3:52 | 9:39 |
| Aug | 15.4 | 5:03 | 8:26 |
| Sep | 12.6 | 6:18 | 6:51 |
| Oct | 9.8 | 7:33 | 5:18 |
| Nov | 7.1 | 8:53 | 3:58 |
| Dec | 5.6 | 9:51 | 3:22 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
Mariehamn averages about 8 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 3 and 13 days.
The sunnier stretch runs 6.3 months, from around Mar 15 to Sep 23. The sunniest month is June, with roughly 12 sunny days (mixed).
The greyest month is January, down near 4 sunny days — about 70% fewer than the June peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 4 | 4 | 8 | 10 | 13 | 12 | 13 | 11 | 8 | 6 | 4 | 4 |
| Sky | Gloomy | Gloomy | Gloomy | Mixed | Mixed | Mixed | Mixed | Mixed | Mixed | Gloomy | Gloomy | Gloomy |
| Sunny days | Sky | |
|---|---|---|
| Jan | 4 | Gloomy |
| Feb | 4 | Gloomy |
| Mar | 8 | Gloomy |
| Apr | 10 | Mixed |
| May | 13 | Mixed |
| Jun | 12 | Mixed |
| Jul | 13 | Mixed |
| Aug | 11 | Mixed |
| Sep | 8 | Mixed |
| Oct | 6 | Gloomy |
| Nov | 4 | Gloomy |
| Dec | 4 | 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 Mariehamn, how humid it feels changes dramatically over the year.
The more humid part of the year lasts 2.3 months, from around June 28 to September 6. The muggiest month is August, when the air feels humid, muggy or worse about 22% of the time.
The most comfortable stretch runs from around September 7 to June 27, and June is the most comfortable month — the air is dry or comfortable 99% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 100 | 100 | 100 | 100 | 100 | 91 | 41 | 37 | 82 | 100 | 100 | 100 |
| Comfortable (%) | 0 | 0 | 0 | 0 | 0 | 8 | 40 | 41 | 16 | 0 | 0 | 0 |
| Humid (%) | 0 | 0 | 0 | 0 | 0 | 1 | 16 | 19 | 2 | 0 | 0 | 0 |
| Muggy (%) | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 3 | 0 | 0 | 0 | 0 |
| Dry (%) | Comfortable (%) | Humid (%) | Muggy (%) | |
|---|---|---|---|---|
| Jan | 100 | 0 | 0 | 0 |
| Feb | 100 | 0 | 0 | 0 |
| Mar | 100 | 0 | 0 | 0 |
| Apr | 100 | 0 | 0 | 0 |
| May | 100 | 0 | 0 | 0 |
| Jun | 91 | 8 | 1 | 0 |
| Jul | 41 | 40 | 16 | 3 |
| Aug | 37 | 41 | 19 | 3 |
| Sep | 82 | 16 | 2 | 0 |
| Oct | 100 | 0 | 0 | 0 |
| Nov | 100 | 0 | 0 | 0 |
| Dec | 100 | 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.
Across the year, average wind speed in Mariehamn is typically breezy, near 25 km/h, and varies a lot with the seasons.
The windier part of the year lasts 5.8 months, from around Sep 20 to Mar 15. The windiest month is December, averaging about 30 km/h (windy).
The calmer part of the year runs from around Mar 16 to Sep 19, with July the calmest month at about 20 km/h.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (km/h) | 29 | 27 | 25 | 22 | 20 | 20 | 20 | 22 | 24 | 27 | 29 | 30 |
| Feels | windy | breezy | breezy | breezy | breezy | breezy | light breeze | breezy | breezy | breezy | breezy | windy |
| Wind speed (km/h) | Feels | |
|---|---|---|
| Jan | 29 | windy |
| Feb | 27 | breezy |
| Mar | 25 | breezy |
| Apr | 22 | breezy |
| May | 20 | breezy |
| Jun | 20 | breezy |
| Jul | 20 | light breeze |
| Aug | 22 | breezy |
| Sep | 24 | breezy |
| Oct | 27 | breezy |
| Nov | 29 | breezy |
| Dec | 30 | windy |
Best time to visit Mariehamn
To characterize how pleasant the weather is in Mariehamn throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around late August, Mariehamn 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 Mariehamn for general outdoor tourist activities is from early July to late August, with a peak score in the last 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 | 0.0 | 0.1 | 1.6 | 3.8 | 5.9 | 5.8 | 4.1 | 1.9 | 0.4 | 0.0 |
| Rating | poor | poor | poor | poor | poor | fair | good | good | fair | poor | poor | poor |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 0.0 | poor |
| Feb | 0.0 | poor |
| Mar | 0.0 | poor |
| Apr | 0.1 | poor |
| May | 1.6 | poor |
| Jun | 3.8 | fair |
| Jul | 5.9 | good |
| Aug | 5.8 | good |
| Sep | 4.1 | fair |
| Oct | 1.9 | poor |
| Nov | 0.4 | 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 Mariehamn for hot-weather activities is from late July to mid August, 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 Mariehamn, 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 18°C), the essentials are rain gear, sun protection and a windbreaker. In the cold season around February (highs near 0°C), pack a warm layer, a heavy coat and a windbreaker.
In August, Mariehamn sees daytime highs around 18°C and nights near 16°C. Worth packing: rain gear, sun protection and a windbreaker. About 10 days see rain.
Sea temperature near Mariehamn
Average ocean temperature at the nearest coast, month by month, banded into swim-comfort zones — the other half of the beach question.
The sea offshore is warmest in August at about 17°C and coldest in February near 1°C.
The water stays below 20°C all year — cool enough that most swimmers want a wetsuit.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 2 | 1 | 1 | 3 | 6 | 11 | 16 | 17 | 14 | 10 | 7 | 4 |
| Comfort | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Cool | Cool | Bracing | Bracing | Bracing | Bracing |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 2 | Bracing |
| Feb | 1 | Bracing |
| Mar | 1 | Bracing |
| Apr | 3 | Bracing |
| May | 6 | Bracing |
| Jun | 11 | Bracing |
| Jul | 16 | Cool |
| Aug | 17 | Cool |
| Sep | 14 | Bracing |
| Oct | 10 | Bracing |
| Nov | 7 | Bracing |
| Dec | 4 | Bracing |
UV index (midday) in Mariehamn 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 Mariehamn peaks around June 18 at about 5 (high) — a little sun protection helps at midday. It bottoms out near December 20 at about 0 (low).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 4 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 0 | 1 | 1 | 3 | 4 | 5 | 5 | 4 | 3 | 1 | 0 | 0 |
| Level | Low | Low | Low | Moderate | Moderate | High | Moderate | Moderate | Moderate | Low | Low | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 0 | Low |
| Feb | 1 | Low |
| Mar | 1 | Low |
| Apr | 3 | Moderate |
| May | 4 | Moderate |
| Jun | 5 | High |
| Jul | 5 | Moderate |
| Aug | 4 | Moderate |
| Sep | 3 | Moderate |
| Oct | 1 | Low |
| Nov | 0 | Low |
| Dec | 0 | Low |
Average hourly UV index in Mariehamn
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 June the burn window is concentrated in the middle of the day: about 7 hours a day reach index 3 (protection recommended). 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 | 0 | 0 | 5.5 | 7 | 6.5 | 5 | 0 | 0 | 0 | 0 |
| UV ≥ 6 (h/day) | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 0 | 0 |
| Feb | 0 | 0 |
| Mar | 0 | 0 |
| Apr | 0 | 0 |
| May | 5.5 | 0 |
| Jun | 7 | 0 |
| Jul | 6.5 | 0 |
| Aug | 5 | 0 |
| Sep | 0 | 0 |
| Oct | 0 | 0 |
| Nov | 0 | 0 |
| Dec | 0 | 0 |
Growing season
The growing season in Mariehamn typically lasts about 278 days, from around March 27 to December 29 — the span where a frost-free day is more likely than not. It is reliably frost-free from April 14 to November 23.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 39 | 30 | 40 | 88 | 100 | 100 | 100 | 100 | 100 | 100 | 93 | 66 |
| Frost nights | 31 | 28 | 31 | 14 | 0 | 0 | 0 | 0 | 0 | 0 | 9 | 31 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 39 | 31 |
| Feb | 30 | 28 |
| Mar | 40 | 31 |
| Apr | 88 | 14 |
| May | 100 | 0 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 100 | 0 |
| Oct | 100 | 0 |
| Nov | 93 | 9 |
| Dec | 66 | 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. Mariehamn banks about 562 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 | 0 | 60 | 192 | 209 | 97 | 3 | 0 | 0 |
| Growing degree days (°C·days) | |
|---|---|
| Jan | 0 |
| Feb | 0 |
| Mar | 0 |
| Apr | 0 |
| May | 0 |
| Jun | 60 |
| Jul | 192 |
| Aug | 209 |
| Sep | 97 |
| Oct | 3 |
| 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.
Mariehamn receives about 2.9 kWh/m² a day of solar energy on average — moderate — with a clear seasonal swing between 0.2 and 6.3 kWh/m².
The brighter stretch of the year lasts 5.6 months, from around Mar 26 to Sep 12. The brightest month is June, averaging about 6.3 kWh/m² (intense).
The dimmest month is December, down near 0.2 kWh/m² — roughly 97% less than the June peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 0.3 | 0.9 | 2.4 | 4.2 | 5.8 | 6.3 | 6.0 | 4.6 | 2.8 | 1.2 | 0.4 | 0.2 |
| Level | Dim | Dim | Moderate | Bright | Bright | Intense | Intense | Bright | Moderate | Dim | Dim | Dim |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 0.3 | Dim |
| Feb | 0.9 | Dim |
| Mar | 2.4 | Moderate |
| Apr | 4.2 | Bright |
| May | 5.8 | Bright |
| Jun | 6.3 | Intense |
| Jul | 6.0 | Intense |
| Aug | 4.6 | Bright |
| Sep | 2.8 | Moderate |
| Oct | 1.2 | Dim |
| Nov | 0.4 | Dim |
| Dec | 0.2 | Dim |
Where is Mariehamn?
Mariehamn sits at 60.1°N, 19.9°E, 11 m above sea level, in Aland Islands. The nearest listed city is Norrtälje, 78 km away.
Topography around Mariehamn
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Mariehamn.
Within 3 km, the terrain around Mariehamn has only modest variations in elevation — a maximum elevation change of 55 m around an average of 7 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 80 m; within 80 km, only modest variations in elevation — a maximum elevation change of 130 m.
The land around Mariehamn is covered by water (44%) and trees (32%) within 3 km, water (55%) and trees (31%) within 16 km, and water (86%) within 80 km.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Mariehamn (60.0973°, 19.9348°, elevation 11 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. 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. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).