Winter Indicators.
Here we are 3 months way from the start of winter,and asking the perennial question" will it be a cold winter? Four of the last five winters have been cold so does the law of averages come into play to redress the balance or could it be cold again?What are the early signals from the key indicators?
1.ENSO.
The latest ENSO diagnostic discussion (Sept 5th) concludes "ENSO neutral is favoured through the northern hemisphere winter 2013/14."For DJF the various models show a split between weak negative and weak positive indices with the average trending slightly positive.Such years are slightly more likely to be accompanied by colder than average winters.
2.SST's.
End of May north atlantic SST,s are generally most closely linked to winter CET.Howebver I always have trouble idenitfying a clear tripole pattern which is the cold indicator.Maybe Gavin P can give his verdict on what signal is coming from May SST's.The pattern seems to show cold anomalies off NE USA and Canada and to the east of Iceland with above average in Mid Atlantic.
3.QBO.
In autumn 2012 the QBO was in negative mode andthis npersoted though winter 2012/13.This Autumn the QBO is in positive territory normally supposed to indicate warmer winters.However this indicator is somewhat unreiable as the cold winter of 2010/11 was positive and the warm winter of 2011/12 was negative!
4.Sunspot Activity.
Cycle 24 is the weakest cycle since the early 20Th century.It now looks as if the peak was 96.7 in Nov 2011,witha secondary peak of 78.7 in May this year.Overall activity level is low and lower than fprecast.However work by the University of readind and METO suggest the strongest link to the CET is at solar minimum.
5.Models.
CFSv 2 shows broadly neutral temperature conditions over the UK,with precipitationslightly below average.The trend over th elast month or seems to have been a shift on th ewarm anomaly towards SE Europe.
Meto tercile probability maps shows no clear temperature sinal obver the UK although warmer than aveage probabilities in the Arctic region.Precipitation is broadly normal and a slight tendency for higher than average pressure to ther north of the UK and slightly lower pressure towards southern europe.
6.Seasonal Pattern Matching.
The very cold dry spring has a 75% chance of being followed bya colder than average winter.The very dry very warm summer is not astrong indicator either way.
7.Conclusion.
Signals are variable all rather weakand suggesting a near average winter.It seems best to llok at the trends in the CFSv2 models and the METO probability maps before making a conclusion at the end of November!
Edited by moderator
07 September 2013 11:38:46
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