My boss in the past looked up the average number of sunny days in St Petersburg in the month of December. The source he found gave an average of zero days. Since you can not have negative days to bring the average down that basically says there is no sun in St Petersburg in December. There probably is a day or two every decade so that rounding brings it to zero.
When I was in the states on facebook people in St Petersburg were posting about seeing the sun. Now today for a short period this afternoon I saw blue skies and sun. It seems this December we have seriously bucked the sun stats. Probably there will be no sun in St Petersburg during the month of December for the next two decades.