January 2012 will go down in the record books as Winnipeg's 3rd warmest January since records began in 1873. The month finished with a monthly mean temperature of -10.8C, 7C above normal, and the mildest January behind 2006 (-7.4C) and 1944 (-10.6C) The month began exceptionally mild with temperatures some 15C above normal over the first 10 days of the month. The only cold weather of the month was between the 17th and 20th when temperatures dropped into the -20s. Other than that, temperatures were above normal nearly every day of the month. The mild weather continued the trend of December which was also well above normal (6C above normal) and ranked as the 9th mildest December on record in Winnipeg. January 2012 marks Winnipeg's 7th consecutive month that has averaged above normal, going back to July 2011.
Top 5 warmest Januarys in Winnipeg (since 1873)
1. 2006 ......... -7.4C
2. 1944 ......... -10.6C
3. 2012 ......... -10.8C
4. 1942 .......... -11.4C
5. 1992 .......... -11.5C
Normal .......... -17.8C (1971-2000 30 year average)
A look at the temperature anomaly map for January (left) shows how the central Prairies experienced the most abnormal warmth during this past month. The persistent warmth this winter can be attributed to a stronger than normal Arctic jet stream which has been generally stuck in a position over the Arctic. This has effectively blocked intrusions of Arctic airmasses southward over the Prairies, while allowing frequent invasions of mild Pacific air from the west. This is a result of a persistently positive phase of the Arctic Oscillation, a climatic pattern affecting the flow of air across the northern latitudes of the globe. This northern oscillation has more than offset the climatic impacts of La Nina, which normally would bring colder and snowier winters to western Canada and the Prairies... an outlook many were predicting this winter. The northern extent of the jet stream has also deflected storms further north, resulting in a notable lack of snow over the prairies, and the 3rd least snowy January on record in the US. Click here for a good summary by Jeff Masters on the impacts of the Arctic oscillation on this year's winter.