Icelanders tend to say that if you don’t like the weather, just wait 5 minutes and it will change.
The Icelandic weather is very different between the seasons and can be very localised also. Be sure to keep an eye on the Icelandic Met Office website during your trip. Below is a short overview of what to expect in different seasons:
The temperature during winter is relatively mild for its latitude, with an average temperature of 0°C on the southern parts of the island and -5°C in the North. The Icelandic highlands usually float around -10°C. Snow is to be expected in most parts of the country as well as strong winds and gusts. The weather can be very unstable during Winter. It usually lasts from the end of October to first half of April.
Spring is considered to last from April until the first half of June. The first day of spring is usually celebrated the first Thursday after April 18th but it’s not uncommon for it to snow on this day. The days are getting longer, the weather more stable and the average temperature is getting higher, with an average of about 7°C. Spring is heralded in by the migratory birds arriving to the island and the flowers blooming.
The second half of June, July and first half of August are considered to be the summer period in Iceland. The weather is relatively stable. Average temperature usually floats around 10-11°C. In the summer of 1939 the highest temperature ever recorded in Iceland was measured (30,5°C) in the East Fjords. Don’t expect that any time soon though!
In September the temperature starts to drop and the weather is becoming more unstable. Autumn storms with very strong winds are not uncommon. The days are getting shorter at a fast pace and the Northern Lights can be seen again. The lush green plants and bushes start to change colours very fast and the average temperature floats around 5°C.