Where is the snow & cold?
Since my early forecasts of last year, I expected the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) to remain dominantly negative during the months of summer 2011 (June, July, August) and winter 2011/12 (December, January, February).
Now although this part of my forecast played out very accurately for my summer forecast, the AO and NAO indices have remained largely positive so far this winter. As I have stated many times before 'this factor has an important bearing on my winter forecast'. I really can't ignore the correlation between the two, as my methods strongly suggest that these teleconnections should already be negative, hence the lack of widespread snow and cold so far this winter.
However there are now some more prominent signs of a huge drop in the AO over the coming weeks, with a more neutral to negative state NAO also occurring. Now when this starts to happen the outlook for some true snow and cold rapidly improves, and confidence begins to grow with the statements I issued on Christmas Day.
1 .January certainly looks promising for this at present, in terms of some true cold and snow across Scotland and northern regions of the UK. Although once again there is likely to be some periods of moderation at times, and this is most likely to be reflected in any areas further south.
2. February should prevail further in comparison to January, and this is when I feel we are likely to see the most severe part of this winter. A cold start to spring 2012 is also possible, with some especially heavy and widespread snowfalls across Britain and parts of Ireland.
3. As I also stated in my 2nd September 2011 update that we could expect “a notable increase in usual wind strengths for this time of year across many parts of the UK, that will result in frequent and potentially damaging gale force winds and strong stormy features throughout autumn and WINTER.”
4. I also stated on the 2nd September 2011 that “Huge swirly low pressure systems also offer the potential for widespread disruption from heavy snowfall across many parts of the UK including the South.”
Now if this pattern change does lead to either or both of these teleconnections becoming dominantly negative, as my winter forecast suggests, then we may still see some records being broken in terms of temperature and snowfall this winter. Another important aspect to consider here, is the length of time this cold Arctic air has been locked in place for. This is also another reason why I have never updated or stated otherwise, in regards to the possibility of records still being broken this winter.
Potentially damaging gale force winds and strong stormy features, are still likely to be a frequent feature at times throughout this winter. However the low pressure systems will offer more in the potential of snowfall than of recently, which could also include areas further south too. February and into spring is likely to see the most remarkable changes if things develop as expected, resulting in frequent and widespread snowfalls across many parts of the UK, with sustained colder temperatures too.
James Madden (UK Long Range Forecaster)
