In Iceland the climate is cold, windy and cloudy for most of the year. Surely it's a cold country due to the high latitude, so that it can receive cold winds from the North Pole, but it's also tempered by the ocean, an also by the mild Gulf Stream that flows in it. The result is a perpetually unstable climate, with sudden changes in weather and temperature, but with a limited temperature range, both between day and night and between winter and summer. Calm and sunny periods are rare. The northern coastal area is colder than the southern one, because it is not reached by the Gulf Stream.
Precipitation is abundant on the southern side, where it amounts to around 2,000 millimetres (80 inches) per year in the most exposed areas, while on the northern side it's much more scarce, so that it descends below 500 mm (20 in) per year, although even here it is well distributed throughout the year. Along the west coast, the amount of precipitation is at an intermediate level, so that in the capital Reykjavik, about 800 mm (31.5 in) of rain or snow fall each year.
Here is the average precipitation in Reykjavik.
Reykjavik - Average precipitation

Iceland is the land of ice, fire and deserts. In the interior there are vast glaciers, from which ice tongues descend towards the plains, while geothermal activity causes the presence of geysers and hot water springs, in which people can bathe even if there is snow around; on the other hand, underground volcanic activity may cause sudden melting of glaciers, with the risk of flooding. It's worth noting the almost total absence of trees, as well as the presence of sandy soils in inland areas, where strong winds can cause dust storms.
In inland areas, there are plateaus and mountains, where the temperature naturally decreases with increasing altitude. Because of the cold summers, snow only melts at low altitude, so the snowline is very low, around 700 metres (2,300 feet) above sea level.
Here are the average temperatures of Reykjavik.
Reykjavik - Average temperatures
Min (°C)-2-2-214799620-2
Max (°C)23361012141411743
Min (°F)282828343945484843363228
Max (°F)363737435054575752453937

The sea in Iceland is cold throughout the year: the water temperature at Reykjavik runs from 3 °C (37 °F) in February, to 8 °C (46 °F) in July and August, therefore it's preferable to bathe in thermal pools...
Reykjavik - Sea temperature
Temp (°C)433346887554
Temp (°F)393737373943464645414139

Along the south-east coast, where a branch of the Gulf Stream runs, the sea temperature is higher, going from 7 °C (44.5 °F) in the winter months, to 10/11 °C (50/52 °F) in the summer months.

In winter, Iceland is not so cold, in fact the average temperature in plains and coasts is around the freezing point. This means that the temperatures can exceed 0 °C (32 °F) quite often even in winter, and rain instead of snow can fall.
Along the northern coast, winter is colder by a few degrees, and here the sea can freeze inside fjords. In inland areas, winter is even colder, especially with increasing altitude. Snowfalls are plentiful along the southern slopes, while they are frequent but less abundant elsewhere. Winter is in any case very long, in fact the temperature rises very slowly during the spring. In April, daytime temperatures are still around 6 °C (43 °F) in Reykjavik. Across Iceland, it can snow from October to May; along the northern coasts, sudden snow showers may occur even in June and September, while in inland areas, due to the altitude this can happen even in midsummer.
During winter, cold air masses from Greenland can lower the temperatures to around -10/-15 °C (5/14 °F), however, these cold spells are short lived, because after a while the mild winds from the south begin to blow again. The cold records are not so low as well, at least for the latitude, being around -20 °C (-4 °F) along the coast, and around -30 °C (-22 °F) in inland areas.

Summer is very cool throughout Iceland. Maximum temperatures exceed 10 °C (50 °F) only in the months of June, July and August. In the capital, during the warmest months, July and August, lows are around 9 °C (48 °F), and highs around 14 °C (57 °F), while on the north coast they are around 10/12 °C (50/54 °F). On the other hand, the days are very long. In Iceland, the weather virtually never gets warm: the temperature rises rarely and for short periods above 20 °C (68 °F). The highest records along the coast are around 23 °C (73 °F), and only in some sheltered inland areas, they are 27/28 °C (81/82 °F).


The amount of sunshine in Iceland is never good, but is generally passable in the late spring and summer, also because of the long days, while it is decidedly low in November in January, when the sun hardly ever shows up.
Reykjavik - Sunshine

When to go

The best time to visit Iceland is summer, from June to August. Spring is cold and it's quite similar to winter, with frequent snowfalls and frosts, but at least the days are longer than in autumn. For skiing and cross-country skiing, March is better than the mid-winter period, because the days are much longer.
As in all the Nordic countries, the length of the day has a significant effect, if not directly on the climate, on the sensations experienced by residents and tourists: the months of late autumn and early winter are characterized by endless nights and very short days, in which the sun remains very low above the horizon even at noon. In Reykjavík, at the winter solstice (21 December) the sun rises around 11:30 am and sets around 3:30 pm. Already in February, the days are longer than in the period from November to January, even though the temperature is not higher.
In summer, the days are long especially in June, when it doesn't get completely dark even at midnight, and in the north, at the summer solstice (June 21) the sun does not set at all, since the extreme north of Iceland touches the Arctic Circle. In the small island of Grimsey, which is right on the Arctic Circle, at the summer solstice the sun is cut into two by the horizon at the moment when it is lower (which happens actually around 1 a.m.). In the island of Iceland, the points closer to the Arctic Circle are the northeast (see Raufarhöfn) and the northwest (see Ísafjörður), which are very close to the Arctic Circle. Already in Akureyri, the sun barely goes below the horizon around 1 a.m., while in Reykjavík, although it does not get completely dark, the sun goes below the horizon from midnight to 3 a.m.
This latter phenomenon, called white nights, whereby the sun goes below the horizon but remains close enough, so that there are still sunset lights even at midnight, in Reykjavik lasts from May 20 to July 23, although some faint lights around midnight are visible from late April and until late August.

What to pack

In winter: warm clothes, fleece, down jacket, hat, gloves, wind jacket, raincoat or umbrella, hiking boots, swimsuit.
In summer: sweater, shirt, jacket, hiking shoes, raincoat or umbrella, swimsuit.