Elliðaárdalur valley is a running spot in Reykjavik. It could be suitable in the winter time as it has has electric lighting.
If you need an open track close to Reykjavik; Varmárvöllur is marked as open to the public and not too far away.
Winters in Reykjavik can get cold and snowy. December through March has a high risk of snow and the temperature is often below -10°C10°F . The days are short and in December it is only bright out between about 1111 AM and 153 PM.
The line represents the average temperature. The faded area represents the most likely temperature span. The temperature is within this area 80% of the times.
The line represents the average dew point. The faded area represents the most likely dew point span. The dew point is within this area 80% of the times.
The line represents the average wind speed.