Part 2 is going provide some seasonal and regional detail that was not covered in Part 1 in the discussion of the NH snow coverage. One of the things I am trying to show in these articles is how normal it is for certain parts of the world to experience a mild (low snow) winter while others are experiencing a harsh (more snow) winter. This year has made headlines by being unusually mild in the United States, but that is one of the only regions that is experiencing a mild winter this year, but the discussion of 2012 remains an article for the future.
The regional discussion of the snow coverage in the NH is centered on North America and the Eurasian continent. 2011 as a whole was slightly below average, but the different regions had different results from each other. That is also normal, but not always the case.
North America: +0.03 million km2
Eurasia: -0.23 million km2
Here is the time series of the two regions over the course of the year.
The periods with less than average snow were mostly in the late spring and summer while the rest of the year had a positive anomaly. Interestingly enough, that has been the ongoing trend over the past 40 years, but the trend is basically insignificant. I am not going to use the technical seasons, but 3 month divisions that are Dec-Feb, Mar-May, June-Aug and Sep-Nov.
For both regions the trend is slightly positive from Sep-Feb and slightly negative from Mar-August.
Here is where a persons individual perceptions tend to cause problems. We remember mostly the abnormal events (like a major blizzard from our youth) and that forms our perceptions of what the climate was like in the past. Then when there is an unusually mild year, we are comparing the two extremes to each other. Only people living in places that have late spring and summer snow extent are seeing a negative trend. The actual winter snow extent is not decreasing in either region.
Local variations do occur. To show this I am going to show the daily snow anomaly maps of the past 13 years. This will show that for the most part, different regions experience different winters, every year.
So while the USA is currently experiencing less snow than average, the northern part of Africa is experiencing the most snow of the entire period of time. A person experiencing snow for the first time in Africa will have a very different perspective of what the climate is doing than someone in the United States.