Afternoon all on TWO.
This post is about the models output, so bear with me, as this could probably also be posted in the Nostalgia thread. It is also the musings of an interested amateur, so those with professional experience, either actual or accumulated through even greater obsession than most on this forum, please go easy on me....
I have been watching the weather since I can remember, which for those of a similar vintage, meant Jack Scott. I grew up in the North West and chose college in Yorkshire because during the 70s (particularly 1979) as it seemed that Yorkshire always got the most snow. I was rewarded by the winters of 84/85, 85/86 and 86/87. I took a job back in the Northwest, but moved to the Southeast in the late 80s (where I am now).
The beauty and strength of modern forecasting models is also their curse. In my childhood, you had to watch Farming Today on Sundays to get an idea of a longer term forecast so we never got any more than around 5 or 6 days' notice of real cold and snow, and that wasn't reliable either.
It seems that now, we exprience winters the are both the real (i.e. the "seasonal" damp and chill we are experiencing down here today) and also winters in an imaginary future. However, the sophisticated graphics and computer power behind them makes the imaginary seem so real and so compelling, that when the models change (or “flip” like many like to say - although they very rarely actually "flip"), we cold fans feel a sense of depression and dejection for something that was "promised" to arrive in the real world, is cruelly snatched away.
Its no longer science predicting a warming world but it is here for us all to see around us (or choose not to see in some cases). However, the full climatic consequences of this warming world, and feedback mechanisms, including changing synoptics, are less clear. So onto today's models...
For me, December as a winter month appeared to be changing. Other than a few days of sleet, hail and snow showers, November and even December (in my recollection I hasten to add before anyone posts stats to the contrary), were generally mobile, westerly months which rarely produced several days of real cold and lying snow in the North west of England. Proper cold spells came in January or February, sometimes from the north, but usually from the east. The big stand out anomaly for me was December 1981, dominated by low pressure and persistent airmasses from an arctic. But it was a one off, or so I thought.
Then came the December of 2009 (which went on into Jan 2010) and December 2010, both experienced by me in the Southeast of England (but similar elsewhere, the latter depositing the deepest undrifted lying snow I have ever seen in lowland UK. My hunch then was that winters (and early winter in particular) were changing. A warming world, particularly the arctic, is leading to the long-term decline of the power of the late autumn jet stream.
And, actually, I think this December is no different and the signs for other recent previous Decembers have also been there, but what cold air was around, missed us. However, what I also think is irrefutably different, is the increasingly problematical access - or even close proximity to - genuinely cold air in December (by that I mean 850s of -10 or colder).
Its clearly around - just look at the Northern Hemisphere charts - but it is much less widespread and in different places than it used to be. This is almost certainly the work of summer ice melt and heat accumulating and then taking time to dissipate in northern landmasses through summer. I wish I had the programming knowledge to throw a net over the winter months and establish a geographical representation (KM2) of the extent of -10 850s (or colder) for the Decembers of today verses previous decades. I am convinced this will show a significant decline over the last 30 years. When you are bored, just take a look at the 850 archives, even allowing for their estimation in early years
I think the synoptics of the last week are a great case in point. I think someone on here called them four cylinder synoptics with a three cylinder outcome, or similar. Even allowing the little transient snow that a number of areas experienced, would these synoptics have delivered an altogether different weather outcome 30 or 40 years ago?
We will have severe cold again, and it will come again in December, but the frequency of it coming and its duration, will continue to diminish. I think the same is true for the Death of the Midwinter Easterly – we could have a similar debate. It will be back, but not as often as it used to visit.
Jeff
Can I just add, what a lovely post. Such a difference from some of the points scoring bickering that pretends to be MO discussion sometimes. Sorry for off topic.