There are plenty of good reasons to visit Iceland at anytime of the year since it’s a newer member on the list of best places to travel on a weak dollar but it also has plenty of other advantages in December, January, and February. 1. It’s Not That Cold.
https://foxnomad.com/2009/12/22/7-reasons-why-you-can-and-should-visit-iceland-in-the-winter/
The tables below list the normal December temperatures and precipitation for cities and towns in Iceland. There's also information on this month's average sunshine and humidity levels. The measures of climate are averages of data collected at weather stations from 1961 to 1990. The weather information covers all sides of Iceland. The capital city of Reykjavik is in southwest Iceland. Stykkishólmur lies north of Reykjavik, on the west coast.
https://www.currentresults.com/Weather/Iceland/temperature-precipitation-average-december.php
Iceland's precipitation peaks in October to February, and is lowest in May and June. Southern and western parts of the island receive the most rainfall. For English-language forecasts or further information on regional weather, contact the Icelandic Meteorological Office (tel.
http://www.frommers.com/destinations/iceland/when-to-go
Iceland has a concentrated tourist season, peaking from mid-June through August. Many Icelanders think the summer tourists don't know what they're missing. Iceland offers plenty to do in spring, fall, even winter, and prices are dramatically lower for airfares, car rentals, and accommodations.
http://www.frommers.com/destinations/iceland/when-to-go
A Weather Guide to Iceland in December. Iceland Mountain Sunset. Jól, Yule, Christmas. December in Iceland is as tricky as it is a treat. Not only is the snow beautiful, it is also the month of Christmas, or Jól (think juletide, as in Yule the words have germanic origins) in Icelandic, and Icelanders take their Christmas very seriously indeed.
http://www.mountainguides.is/blog/a-weather-guide-to-iceland-in-december/
Iceland in December. Despite the cold weather and short hours of sunlight, December is actually a great time to visit Iceland. Early in the month, you can take advantage of low-season savings, and if you come over the holidays you’ll find a delightfully festive atmosphere. The temperature ranges from 2.2°C to -2.8°C, or about 28 to 36°F.
http://www.whygoiceland.com/december-in-iceland.html
… and other questions you might have about travelling in Iceland in winter. Iceland has a bad reputation when it comes to winter. Sure, the name of the country doesn’t help (and no I’m not going to follow up with the story of those confused vikings and Greenland) but winter in Iceland is really not that bad. It’s not as cold as Minnesota, for example, and not as dark as Tromsø.
http://iheartreykjavik.net/2013/11/whats-the-weather-like-in-iceland-in-winter/
It’s Not That Cold. Iceland was named by Norwegian Floki Vilgeroarson after he encountered quite a bit of ice when he originally landed in the north. Yet due to the warm Gulf Stream current, the average temperatures in December stay around 0C (32F) and don’t hover more than about 2-3 degrees warmer or colder.
https://foxnomad.com/2009/12/22/7-reasons-why-you-can-and-should-visit-iceland-in-the-winter/
There doesn’t have to be snow for Iceland to be amazingly beautiful in Winter. If there’s one word that best describes the Icelandic weather experience it would be unpredictable. What that means is that we can’t really tell you what the weather will be like because we just don’t know.
http://iheartreykjavik.net/2013/11/whats-the-weather-like-in-iceland-in-winter/
Fewer Tourists. Seeing as this month is the middle of winter in Iceland, there are many fewer tourists, but you ought not to let the cold weather discourage you from visiting in the month of December. Most tourists will miss out on some of the greatest parts of Iceland simply because of this.
http://www.mountainguides.is/blog/a-weather-guide-to-iceland-in-december/
weather in iceland in december
In Iceland the temperature ranges from 2.2 degrees Centigrade to -2.8 degrees Centigrade or about 28 degrees Fahrenheit to 36 degrees Fahrenheit  during the December. 