Weather in Iceland
The weather in Iceland is fickle and impossible to predict. It's not unusual to go from snow showers to bright sunshine within 20 minutes and vice-versa. Be prepared for anything!
Summer in Iceland is in July. August can be nice, but often autumnal showers and winds have swept in, especially after the middle of August. Summer temperatures can hit 25 degrees when the sun is shining, which feels much warmer than it sounds, plus you have light 24 hours a day. The problem with summer is that there are lots of tourists, flights are more expensive and accommodation books up way in advance, especially at the cheaper end of the market.
Winter in Iceland is from October to April. Snow, sleet, high winds, darkness etc, but you can also have blissfully clear, still days (unlike many places in the UK). It's pot-luck what you get and the weather can change within half an hour. However you may get to see the Northern Lights in winter - out of built-up areas there is a high chance you will see the green glows floating across the sky on clear, moonless nights. (I have even seen them on August 18th! in Reykjavik, so you never know...)
The winter of 2007 has been the worst on record with North Atlantic gale force 12 storms hitting as often as twice a week! Flights to and from the island have been cancelled twice so far, which apparently, is highly unusual......
The rest of the year is wet and windy, but it's never that cold. Iceland is warmed by the Gulf Stream so it's never as cold as Finland, Poland or Russia during the winter, even though it's a stone's throw from the Arctic Circle. Temperatures hover around freezing point in Reykjavik during the winter but descend the more north and east you go (likewise in summer, it's hottest and driest in the North-East). The sun only just dips below the horizon in Reykjavik in May, June and July which means it's always light outside, and likewise in winter it appears for only a few hours, thus confining the country to endless twilight.......
You can check out the current weather by looking at a live webcam in Reykjavik.