iapennell

Westerly AAM pumped polewards leading to a strong Jet-stream: Could this mean December 2016 is NOT going to have lots of frost and snow as some anticipate but instead a good dose of mild stiff Ferrel Westerlies bringing their buddy Wet Wet Wet ( )!!

-5C recorded last night at my little AWS at just over 400 metres above sea-level near Alston in Cumbria: I expect something a bit colder than the -6C which is the lowest it got last winter, I'm going for -9C during one of the cold frosty spells I predict for Jan/Feb 2017, but nothing lower. I am not actually expecting a severe winter!

A proper definition of the seasons and what month falls into what seasons should take account of two or three important factors, the first of which is astronomical. The length of day is shortest over the three months November to January and because the length of day and elevation of the Sun at noon varies like a Sine curve (little change either side of the Solstices, rapid changes near the Spring/Autumn Equinox this would suggest the Winter and Summer seasons ought to consist of four months each and the transition seasons of Spring and Autumn just two months each. The elevation that the Sun reaches (and the length of day) on 26th October and 18th February is exactly (with very small variation from year to year) midway between the elevation the Sun reaches at noon (with exactly 12 hours' day-length) at the Equinoxes of 22nd/23rd September/20th March on the one hand and the low elevation the Sun reaches (with shortest day-length, little over seven hours near Carlisle or Newcastle) at the Winter Solstice on 21st/22nd December on the other hand. By this definition November, December, January and February should be classed as winter months. The second important factor determining what season a month should fit into is meteorological: The prevailing temperatures, rainfall and sunshine amounts, average incidence of heat in the warmer months and frost/snow near the winter help one decide what season a particular month should go: November is, on average warmer than the three months following it by 2 to 3C and it is also a little warmer than March (has less frost or snow than either these other months), thus it should be defined as an autumn month. However, as with changing daylight levels the average temperature changes a bit more rapidly on the whole in the transition seasons than when it is near the time of lowest average temperature in this country. The average temperature in November is roughly mid-way between the mean annual temperature and the average temperature of the coldest month, in some years warmer and some colder; and with rainfall amounts and light levels on average not far from the mid-winter norms one could justify calling November a winter month (particularly in the north of Britain when the first snowfalls can occur in November). However, also from a metrologist's perspective, it is convenient to classify November as an Autumn month if only to ensure all seasons are equal length and for ease in calculating seasonal and annual temperature, rainfall and sunshine means in a given location: I would thus include November in calculating average temperatures, rainfall and wind-speeds and also (as pointed out above) the official Meteorological definition of Autumn is from 1st September to 30th November (though if you lived in Siberia or northern Canada they might have a different "Official Definition" with October through March being "Winter"). A third defining factor in deciding what months should be in what seasons ought not only to be average conditions but the POTENTIAL for extremes of heat and cold, weather associated with intense radiative heating or intense radiative cooling SHOULD the right conditions occur: And it is clear November ought to be a winter month based on such definition. Extremes of weather affect communities more than average hum-drum conditions. In November, the day-length is approaching it's minimum- where I live in the North Pennines the day-length is eight hours by mid-month and nearer seven by the end of the month (by which time the Sun is no more than 13 degrees above the southern horizon at noon) and nights are long. When conditions are right with clear skies and calm for more than a few days hard frosts can occur; freezing fog can form and persist in valleys keeping daytime temperatures there well below freezing; this is especially true if winds over preceding days have come from the Arctic or northern Russia (which are very cold source-regions by mid-November): Persistent hard-frost and freezing fog is severe winter weather by most folks' definitions. Really extreme cold can happen in November if clear dry conditions follow Arctic winds that bring snowfall and establish snow-cover: In Braemar, Scotland a temperature of -23C was recorded in November 1919 (that's just 4C warmer than the all-time record low of -27C recorded in Britain) in just such circumstances; parts of highland Scotland had daytime maxima as low as -10C in late November 1985. It is also possible very cold air to build up over Russia, move west and south under the influence of strong high-pressure over Arctic Scandinavia and meet mild moist air over southern England associated with a depression over northern France to bring widespread disruptive snowfalls- as happened in late November 2010. These sorts of extremes would be regarded as severe, if not dangerous, winter weather. At the other extreme, strong baroclinicity can (and does sometimes) develop between the already-frigid Greenland/NE Canada and the still mild North Atlantic to bring about the formation of deep depressions with centres below 960 mb that pass over/south of Iceland to bring severe south-westerly gales and torrential rains to much of Britain in November: This brings storm-damage and flooding, whilst removing any remaining leaves off trees- conditions that most would associate with winter .By such reckoning that makes November a winter month. I can understand folk in the South would consider November an Autumn month, in most years they have to wait until then for their first air-frost and the trees in southern England still have their leaves in full autumn regalia until mid-month but this is certainly not true in Scotland and trees are bare (and garden flowers dead- as a rule) across the whole of Britain by the fourth week of November. If I was asked where to put November as a whole I would say early winter, though I would say that just early November is late autumn and (as a Northerner) would classify early March as late-winter rather than Spring. But for calculating averages I, along with most meteorologists like to keep the seasons equal and would thus lump November with Autumn and March with Spring to keep the calculations simple!

Whether snow or not, there is every chance of many folk in Britain waking up to their first really sharp frost of the winter (min air temp -3C or lower) by Sunday morning with this set-up: Arctic air pushing south-east over Britain by Saturday (origin Greenland)!

@Hocus Pocus; It's fine, I'm not one to take offence and it is good we can have robust arguments and discussion about our favourite subjects! I did predict the weather would take a more unsettled and stormier turn heading towards December, have not abandoned that and will not do so. I did also state that this winter was not going to be as wet, stormy or mild as last winter and that there will be some cold spells; that however the season would still pan out milder and wetter than usual (this I pointed out at the outset) and the most recent patterns seem to be vindicating these assertions. We are having a very mild run at the moment. Temperature here is 12C at present after a drizzly day with south-westerlies (this at over 400 metres' elevation in the North Pennines), though we had our first snowfalls of the winter last Wednesday (9th)! Westerlies with low-pressure over Scotland or to the north forecast for next few days though colder north-westerlies look set to happen later. The cold dry and frosty run is not happening at the moment but cold frosty weather is flagged up for later this month assuming the long-range outlooks prove right.

The modern terms I have to be familiar with my AAT Accounting Course are the Income Statement and the Statement of Financial Position (for the Balance Sheet). That said, I only brought this into a discussion of my predictions for the coming winter to clarify why I do not think this winter will be a cold one. The situation high above the Equator is like an Accrual of Westerly (income) and with the QBO average of 29 mph from the West at the 30 mb level (and Westerlies also at 50 mb over the Equator) a substantial one at that. And like the bosses and managers in a business would stand to gain from the business accrual of income rather than those on the streets living in boxes the baroclinic zones of the far North Atlantic (a bit further north this year) will be the likely recipient of that accrued Westerly AAM when it touches down (as indeed it must). That is basically the analogy I have been trying to make when conveying my reasoning as to the forecast for the winter that I have made.

@ J10, Granted, there are some differences but since the overall heat and Westerly Momentum of the Earth-Atmosphere System changes very very little, if at all, there are analogies with Accounting. Depreciation of Fixed Assets is a case where the value of the asset reduces over time but (clearly) there is no beneficiary for the loss of value; yet the loss of money is accounted for through an Accumulated Depreciation Account. A Government that does a bit of Quantitative Easing arguably creates money in it's Central Bank, no-one is taxed or fined to pay for it! What matters is that when you do the end of year Accounts all beneficiaries and payers, assets and liabilities are accounted for and both sides of the Trial Balance should balance. That is not to say that a business or organisation does not make a Profit or Loss, but the difference, transferred to a Profit and Loss Account would still make the Ledgers Balance. As regards heat, there is the heat created by radioactive decay of elements deep inside the Earth (the main reason the interior of our planet is incandescent and semi-molten- and has been so for billions of years) and this is balanced by the conduction and convection of heat to the crust and it's loss through volcanoes and the like. The extra CO2 in the atmosphere also means slightly less heat is radiated back into space than is received from the Sun (and from the Mantle) during the course of a year but all heat can still be accounted for, where it is stored and the "transactions" that occur between ocean-atmosphere, Earth-atmosphere, low-latitude atmosphere to higher-latitude atmosphere, can likewise be totalled and both sides of the Ledgers should come to the same amount. Likewise with Westerly Momentum, there will be all the Ledgers with differing stores of this Momentum (the Equatorial Stratosphere has money in it, as it were, with winds being Westerly there at present) but when you add up all the Ledgers and account for all the transactions over the year, both sides of the Ledgers should come to the same amount. There may be small gains or losses from outside the Earth-Atmosphere System in total but these are also almost always negligible in the case of Westerly Momentum (and in Accounting terms you would have a Westerly Momentum Lost to Earth Account to make the Ledgers balance). Talking of Accruals, there is an Accrual of Income (for mid-latitudes) being built up by the strengthening NE Trades caused by cooling over the subtropical continents of North Africa and southern Asia strengthening the subtropical high there as we go into winter: The Westerly Asset stored high above the Equator is set to contribute to this Accrual of Income (Westerly AAM due to be exchanged from the Higher-Latitude Troposphere Account to the Higher-Latitude Ocean and Higher-Latitude Earth Accounts!!). And that ain't good news for the cold-weather lovers on here!

@ chrisbell-nottheweatherman; As in Accounting where you move money between different ledgers, the total Angular Momentum of the Earth Atmosphere System remains constant (as required by the Law of Conservation of Angular Momentum). This is not actually strictly true all of the time because there are outside forces that act on planet Earth and it's atmosphere (i.e. tidal frictional effects of the Sun and Moon against the atmosphere and oceans as the Earth rotates, smaller effects due to meteorites and out-gassing of the top of the atmosphere where this finally escapes into space). The Earth is slowing down, which is why Greenwich adds leap-seconds at the end of each year- but it is a slow process that has little overall impact on the weather in this (or any other) part of the World. For practical purposes and for the vast majority of of the time these outside forces are negligible so in terms of Westerly AAM what goes up must (eventually) be returned to the surface and the total amount of Angular Momentum of the Earth-Atmosphere system remains constant. Hence if large amounts of Westerly AAM is added to the atmosphere through frictional interaction of NE Trade Winds (and Polar Easterlies) with their underlying surfaces and there is already a large store of Westerly AAM in the Stratosphere it is not unreasonable to suppose that this will be returned to the surface in the most favoured locations (these tend to be just southwards of the main baroclinic zones in higher latitudes, such as between the Arctic interior and the North Atlantic Ocean). Heat can be treated in a similar way: The interior of the Earth is a store of a tremendous amount of heat but because of the thickness of the crust a relatively small amount leaks out to the surface- most of this happens in volcanoes (most of which are under water and form part of the mid-ocean ridges. By far the biggest incoming of heat is that from the Sun and because of rising CO2 levels the heat coming in from the Sun (and up from the mantle, chiefly via volcanoes) exceeds what is lost to space by about 0.25 Watts per square metre when averaged over the globe over the course of a year (however this could change and the global sign become negative with this Grand Solar Minimum about to commence). The starting point is not, therefore, a zero sum game but there is a consistent gain of heat radiation (as averaged over the year) between 40N and 35S- which has to be balanced by heat transport away from this vast region (via atmosphere and ocean) to stop it getting hotter and this heat is transported into middle and high latitudes of both Hemispheres where there is a net radiative loss (preventing those areas cooling down). Heat is transported via radiation, via conduction from the mantle, via ocean currents (this is the link with Angular Momentum) and via the wind (in Accounting terminology, akin to the transactions of money) and all component parts- oceans, ice-sheets, tropical stratosphere, tropical troposphere, higher-latitude atmosphere, higher-latitude stratosphere will all contain (in their Ledgers, to use an accounting analogy) a certain amount of heat at any fixed moment in time and they will also have so much Westerly Angular Momentum relative to the Earth beneath them. But as averaged over the year the total amount of momentum and heat contained across all the Ledgers, as it were will not change (Angular Momentum) or change little, if at all (as with heat). The oceans themselves are extremely important as a store of heat, particularly when ocean temperatures are warmer or cooler than usual over extensive areas because of their great heat capacity. The oceans are also a big store of Westerly Angular Momentum on our rotating Earth (owing to their sheer mass) because the direction of ocean currents near the surface or at depth represent movement of vast masses of water relative to the rotating Earth below. In higher-latitudes strong westerly winds blowing over the ocean surfaces (as is often the case in winter over the North Atlantic) leads to a loss of Westerly AAM from the atmosphere and an equal gain in the equivalent amount of momentum for the underlying water surfaces through frictional interaction between the surface waters and the Westerly winds blowing over them- and that in turn leads to the surface currents. This, for example, partly explains the existence of the North Atlantic Drift. The Westerly Angular Momentum of the oceans that results does not disappear but the eastward-moving surface currents lose this momentum through frictional shear with the more sluggish deeper waters, through the resistance this eastward-moving current encounters on reaching shallow continental shelves and coastal areas of Western Europe and (of course) when easterly winds blow over these eastward-moving waters the water loses Westerly momentum to the atmosphere- again through frictional interaction between the water and the surface winds. In the tropics and subtropics of both Hemispheres, persistent NE and SE Trade Winds reduce the absolute westerly momentum of ocean surfaces on our rotating planet. In accounting terminology that is a cost, which leads to surface ocean currents flowing westwards against the direction of the Earth's rotation: These are the North Equatorial and South Equatorial Currents across both the Atlantic and Pacific and these too are very important because they control macro-scale developments like ENSO. These currents also give up their easterly (negative) momentum to deeper ocean waters and ultimately lose momentum when they reach the eastern coastal shelves of the Caribbean, Brazil, SE Asia, the Pacific Islands of Polynesia and Micronesia and coastal eastern Australia. On the whole, the great oceans must have relative angular momentum close to zero, the deficit in the Westerly momentum account of tropical, subtropical and polar waters (due to the Polar Easterlies) being more or less matched by the surplus (i.e. Westerly) momentum of currents in mid-latitudes; waters at great depth have little eastward or westward momentum overall. During the course of the year, whilst surface currents are locally significant, there is little significant overall change to the amount of Westerly Momentum stored in the Great Ocean Banks (again to use an accounting metaphor).

@Hocus Pocus; I STILL rule out any month this coming winter being colder than usual- there is too much warmth stored in the NE Atlantic and developments in the half of the Northern hemisphere between 30N and the Equator (see above) do not lend themselves to any prolonged spells with northerly or easterly airstreams. I did say, at the outset, that I expected this winter to be milder and wetter than normal overall but not as mild nor as wet as last winter. There will be a couple of cold spells- with hard frosts- this winter (from the east or south-east), that I predicted back in early October when I first made the forecast but I am still not predicting a cold winter. Yes, I modified my predictions for November/December in light of the surprise increase in Eurasian snow-cover and the blocking patterns evident in outlook charts recently (btw. Matt Hugo does this, too as do other organisations providing long-term seasonal outlooks), but it has been ONE update and all I did was revise downwards the projected CET for Nov/Dec by about 1C overall and knock an inch or so off the England and Wales rainfall projections over both months. I have not changed the February 2017 outlook at all (and see no reason to at this stage).

BTW do any of you know about Accounting? I know this is a strange topic to bring up on this Forum but I am currently studying AAT Advance Diploma in Accounting and are familiar with how assets, liabilities, capital, expenditure and income are accounted for: A business is healthy with good prospects if it has lots of assets, has goodwill and is profitable- any Accountant will tell you this. Likewise, as you can divide money up this way, there are parralels as to how heat and momentum can be divided up. So then, we have a situation where large amounts of heat are stored in the oceans at higher latitudes, the Northern Hemisphere has been (overall) absorbing more heat than it has lost over several years and there is a large amount of this heat stored into the oceans-particularly just west and north of Britain and this country is likely to be a benefactor of this stored heat in the coming months as it is released into the atmosphere. Overall, thanks to the laws of Conservation of Angular Momentum, the Earth-Atmosphere system only leaks very small amounts of momentum to Space (chiefly through out-gassing and marine/atmospheric tidal friction due to the Sun and the Moon- the latter being much more important). However, to follow the Accounting analogy Westerly AAM as transferred between and stored in different Ledgers": In this case these ledgers would be the solid Earth, the oceans, the Troposphere and the Stratosphere/Mesosphere and with regards to the surface Easterlies are expenditure and Westerlies income. When excess Westerly AAM is stored in the Troposphere or in the stratosphere (i.e. Westerly QBO's) and there is a strong transfer of Westerly AAM into the atmosphere at low latitudes increasing this store, the atmospheric ledgers of Westerly Momentum would soon be bursting to the brim: As such these factors increase the prospect for Westerly AAM to be returned to the surface (using Accounting analogy there are assets and money in the bank for a businessman to draw upon for personal use). This only happens if there are Westerlies interacting with the underlying surface with the frictional impact with these causing a loss of Westerly AAM. In other words, I hope that you can appreciate why both the heat and momentum budgets are such the they don't point to a hard winter in Britain.

A look at the QBO at the 50 mb level (lower down in the Equatorial Stratosphere) shows that this, too, has become Westerly as averaged over the last month (average for October 1016): https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwigx6Th8KDQAhVKBsAKHVMbDWcQFggwMAA&url=http%3A%2F%2Fwww.cpc.ncep.noaa.gov%2Fdata%2Findices%2Fqbo.u50.index&usg=AFQjCNHz_FLh4h2v0CwU-FxJAAf2pd5Jeg Given the fact that October's QBO average at the 30 mb level was also 12.9 m/s from the West (about 29 miles per hour), this is not something that can be discounted. Now,IF ONLY both the 50 mb and 30 mb QBO's had averaged 10 metres per second (or above) from the East: then I'd say, what with the extensive Eurasian snow-cover we have combined with the Lá Nina in the Equatorial Pacific- then we could be talking!! Unfortunately, that is not the case and you can see (comparing the Stratospheric winds at the 50 mb and 30 mb levels) how the Westerliness of the QBO is working down through the Stratosphere. When it reaches into the Equatorial Troposphere it quickly gets into the Global Circulation providing an extra source of Westerly AAM. You can appreciate from this why I am not predicting a cold and snowy winter for the UK. Of course, a number of factors impact upon the strength of the Westerlies in higher latitudes and thence on the British winter weather that we can expect but the QBO is a pretty major influence. Furthermore, the patterns of sea-ice extent and ocean-surface temperature anomalies indicate to me where the likely sinks for excess Westerly AAM are going to be at the surface; Arctic sea-ice is slowly recovering from it's record Autumn lows and over the newly formed pack-ice it will, of course, get very cold and this will propagate up into the Arctic atmosphere making that very cold (and reducing thickness heights over the Arctic in the process). Over the warmer-than-normal North Atlantic and North Pacific waters on the periphery surface air and air higher in the atmosphere is warmer and thus thickness heights will be higher and between the two will be a substantial baroclinic temperature and pressure gradient: What does that tell you about the likely passage of depressions? What I take away from the facts about the QBO is that there is a major store of Westerly AAM, currently in the Equatorial Stratosphere, this is slowly working it's way towards the Equatorial Troposphere from where it will quickly enter the Northern Hemisphere General Circulation. The increasing strength of the NE Trade Winds going into winter will increase the uptake of Westerly AAM for the Northern Hemisphere General Circulation as a whole, this fairly quickly leads to an increase in the speed and strength of the upper Westerlies further north and if baroclinic factors concentrate this towards the northern North Atlantic (as seems likely this coming winter) then we can kiss good-bye to high-latitude blocking by January. However, there is a small caveat (or consolation!) caused by the rapid increase of scow-cover over Eurasia that could alter the scene quite dramatically: Increased snow-cover over central Asia would increase the surface albedo locally resulting in further regional cooling beyond the normal seasonal cooling that occurs- and crucially this leads to reduced mid-tropospheric thickness heights north of the Himalayas and the Central Asia Pamirs. That in turn would increase the strength of the high-level Westerlies that would then blow strongly against the highest parts of these mountain ranges (these mountains, rising to 7,000 metres or higher) are not far beneath the sub-tropical jet-stream (which itself would be strengthened, displaced equator-ward a little and further reduced in altitude by the effect of extensive snow-cover further north). The strengthening NE Trade Winds (whose frictional interaction with the underlying surface leads to an increase in Westerly AAM for the Northern Hemisphere as a whole) combined with Westerly AAM coming from high-up over the Equatorial Stratosphere would also help strengthen the subtropical jet and assist possible cyclogenesis over Central Asia= between the snow-covered rapidly-cooling North and the still-warm subtropics. The resultant Westerlies would be very strong over these mountains (easterlies north of such depressions would be weak aloft). Thus the Himalayas and Pamirs could well become a major sink for Westerly AAM which would mean less need for strong Westerlies over the North Atlantic and North Pacific with, for the United Kingdom, much greater scope for cold dry high-pressure conditions from northern Europe to affect the winter weather. Because of all this, I very much believe this coming winter will certainly be colder than last winter overall, but there is no way I would predict a deep-freeze for either January or February. Likewise there will be much less rain this coming winter (probably more snow for most) but there will still be wet and windy spells across the country. And the effects of rising Westerly AAM in the Northern Hemisphere Circulation (from the effects of the NE Trades and Westerly QBO reaching downwards over the Equator) will be felt in the UK soon- at any rate by the middle of the next month: Of that, I can be sure!

Quasi Biennial Oscillation average for October shows further increase in the mean strength of the Westerlies (to 12.9 metres per second), Arctic sea-ice at record low for early November but slowly increasing and sea-surface temperatures above normal to the north of Britain: Westerlies to the north augmented by likely baroclinicity Canada/Greenland-far North Atlantic and also (later) by the signal from QBO. I would re-iterate that I do not expect really severe and/or prolonged cold in January/February 2017- even though cold water patch in mid North Atlantic could result in the splitting of the Circumpolar Vortex at times with one part moving south-east over the Med at times.

@Matthew Wilson; If one has concrete reasons to believe the main baroclinic zones (and thus the storm tracks) are pushed up to 70-80N in the European Arctic sector- based on where the very cold air over the pack-ice would meet much warmer (and warmer than usual) sub-arctic waters then yes, there is a possibility of the depressions (and even the extensive south-westerlies associated with them) missing much or all of the United Kingdom. That said, the further north the storm tracks are pushed, the stronger (and more extensive) the associated westerlies because they have to blow harder and more extensively to counter-balance the frictional effects of tropical and polar easterlies when they are closer to the axis of the Earth's rotation. A strongly Westerly QBO is also Westerly AAM stored in the (Equatorial) Stratosphere and sooner or later this, too, must find a sink [at the surface- probably in higher latitudes]. There is a patch of cold water in the mid North Atlantic, which will assist in splitting off the southern portion of the Circumpolar Vortex so some depressions (and Westerlies) can make that a sink for some of the accumulated Westerly AAM. If that happens the sub-arctic Westerlies won't need to be as extensive and Britain could fall in the gap between- into which cold high-pressure from Russia can penetrate. That is the only basis on which I can make any prediction of dry cold and frosty spells; hopefully though this gap between the Mediterranean and Arctic depressions really materialises and proves it's worth: You cannot beat the surreal experience of a countryside glittering thick in hoar-frost under a full moon whilst the -10C air scrubs one's lungs!!

@mcweather, Interesting to go back through the archives to see whether I would have predicted recent cold winters: In October 2008 there was cooler-than-normal waters just west of the UK but warmer than usual to the north, the Arctic ice extent was below the long-term norm but not so much as this autumn and there was a pronounced Lá Nina in the Equatorial Pacific. I would have predicted a more northerly path of storm tracks based on warm waters in the sub-arctic but with Arctic pack-ice not much below normal still likely to get very cold (over the ice) and generate strong baroclinicity along the margin of the pack-ice. The QBO was positive (Westerly) at the time. However, cooler than usual waters just west of Britain predicated high-pressure being more likely to occur there and Lá Nina suggests weaker NE Trade Winds over the Pacific. There was also a BIG increase in north America and Russian snow-cover in autumn 2008 and also the previous Sunspot Cycle was falling away. On the basis of all these pieces I would have predicted a slightly colder than average winter, most storm-tracks liable to pass well north of Britain (but not all of them) with plenty of dry frosty weather but also some mild wet spells. I would have expected some high-pressure to push in from Russia to bring very cold air off frozen snow-covered Eurasia but not to a great extent. The Westerly QBO would have got me thinking that that would affect Britain later in the winter (bringing strong westerlies), I would probably not predicted the very cold and snowy start to February in 2009. In October 2009 the mid North Atlantic was slightly cooler than average but waters north of Britain were 2 to 3C warmer than normal for October. Arctic ice was well below normal and this would have predicated strong storm tracks in winter over or possibly north of Iceland but with the cool mid North Atlantic (slightly) increasing the likelihood of high-pressure there. However, in autumn 2009 there was by then a weak El Nino and snow-cover over Russia and North America had not increased to the extent it had in autumn 2008. More than outweighing these were the very quiet state of the Sun and the fact that the QBO was strongly easterly (mean wind-speeds up to 30 mph) at the 30 mb level. On balance, and given the temperature of the ocean surfaces north of Britain I would have gone for a drier than usual winter with temperatures only a little colder than normal because the pattern of sea-ice/warmer than usual water to the north would have indicated to me stronger storm tracks towards the Arctic that would largely have prevented Arctic air reaching Britain. I would have expected however, from the cool waters just west of Britain, that there would be an increased chance of spells with bitterly cold high-pressure from Russia due to the southern portion of the jet-stream splitting and carrying some depressions into the Med leaving open the possibility of the Siberian High extending westwards. In 2009, after over 20 years without really severe winter weather, I had come to believe that because of the somewhat reduced extent of Arctic ice combined with warmer than usual seas north of Britain that really hard winters were unlikely to occur again barring some major disruption like a thermohaline shutdown in the North Atlantic or a powerful volcano or two. That's what I believed then and if I am honest, I would not have predicted 2009/10 to be really cold based on the sea-surface temperatures, ice-cover extent, snow-cover over land, etc. In autumn 2010 the QBO had been strongly Easterly and only became weak westerly by September by which time Lá Nina was setting in in the Equatorial Pacific (following a strong El Nino earlier in the year). The Sun, at the end of the last Sunspot Cycle at that time was very quiet- all pointers to a cold winter with plenty of blocking (at least in the early half- as the residue of Easterly QBO worked out of the Northern Hemisphere circulation). However, in October 2010, although there was extensive snow-cover over Eurasia, sea surface temperatures to the west and north of Britain were well above average for the time of year but there was cooler than normal water off the USA East Coast. Arctic sea-ice was below normal but not unusually so- strong baroclinic gradient between warm sea and very cold Arctic not far from Iceland and I would have predicted January/February 2011 to have been mild and stormy on that basis (true for February 2011). I would have expected cold spells during the early part of the winter- probably from the east but nothing as severe as actually happened and I would have anticipated mild wet spells that for November/December 2010 based on the anticipated strong baroclinic zone around Iceland (early November 2010 was indeed very wet- the SSW that occurred over the Arctic later meant that the weather later became much colder as winds turned north-easterly). I hope this answers your question.

I see that the Quasi Biennial Oscillation in the Equatorial Stratosphere (30 mb height) has Westerlies which further increased in strength last month (to average at 12.86 metres per second- almost 29 miles per hour from the west- as averaged through October! With sea-surface temperatures north-west of Britain still warmer than usual this does not bode well for serious cold and snow later in the winter, though that's not to say there won't be some cold snaps! The rapid increase in snow-cover across Eurasia, the record-low extent of Arctic ice-cover- the ice-margin is still right up at 80N in the European Arctic (so a real chance of depressions missing the UK entirely and heading deep into the Arctic) and of course the fact we have a weak Lá Nina means that we are unlikely to have anything like a repeat of last winter nor winter 2013/14 (that winter delivered for the North Pennines not one really hard frost, the coldest it got was -4C in late November). The declining phase of the Sunspot Cycle also increases the scope for some colder weather but we do not have a totally quiet Sun as yet. Btw we had our first snowfall of the season today at just over 400 metres' elevation in the North Pennines. Almost all thawed away now, but we did have an inch of snow-lying (and clearly more on the higher fells).

In which case, why would one try to make predictions for the season ahead?!! The fact remains, that there are several macro-scale pointers (that are very unlikely to change in the space of a few months), like the El Nino Cycle, the wind-pattern high over the Equator (Quasi Biennial Oscillation), pronounced sea-surface temperature anomalies north and west of Britain (and where these are) along with marked seasonal Arctic sea-ice anomalies not to mention where we are in the Sunspot Cycle that tend to hold true over longer periods of time that one can use to make a prediction. That is not to say unforeseen events cant or wont knock the prediction off course, but using the macro-scale variables to make predictions for the season ahead (particularly for a season in which the Circumpolar Vortex is liable to settle into a particular pattern and stay there- and one can ascertain where the likely baroclinic zones affecting it, and therefore the storm-tracks will be) is likely to produce more accurate forecasts over the long term than going by more transient features like blocks on weather charts. That's not to say weather charts and model runs up to three weeks out are not valuable, particularly on approaching the beginning of our predicted season, but they tend to show up to three weeks ahead at most. Blocking highs over Scandinavia in themselves can encourage cold and snow-cover over Europe that might lead to a tweaking of the early part of a seasonal prediction in a colder direction; but both the block and European snow-cover are transient features that can be swept away should the Circumpolar Vortex strengthen, the Rossby Wave pattern shift east to place an upper trough just west of Norway and milder south-westerlies remove the European snow-cover! Even the forecast models can get these wrong! However, strong sea-surface temperature anomalies, El Nino Oscillations and high-latitude sea-ice anomalies almost never change that quickly (owing to the very large specific heat capacity of oceans) so they can be relied upon more in making seasonal predictions.

@Radiating Dendrite, @Hocus Pocus. This is why the title of this thread, when I made the original prediction has the description "Preliminary Prediction" in it. You cannot be 100% certain and the large-scale parameters that (given what they were a month ago) were expected to be in a particular state based on seasonal changes changed somewhat in unexpected ways. There is always a possibility of this happening, but if for example, Arctic sea-ice is at near record lows and the sub-polar oceans are 6C warmer than usual in September you can be pretty confident that the sub-arctic waters will still be seasonally warmer than normal by December/January and that Arctic ice will not have recovered to normal winter levels by then if the surrounding waters are warm because of the very high specific heat capacity of water: Even exceptionally severe cold over these sub-arctic waters would struggle to cool sea-surface temperatures down to normal for winter if the early autumn averages were 6C warmer than normal. Thus I did feel safe in using these parameters, predicting with a measure of confidence that the sub-arctic oceans would remain mild and that this would have an impact going into winter. The Quasi Biennial Oscillation is another case in point, in September it averaged over 10 metres per second from the west and it is not a wind-pattern that changes quickly, it also slowly filters down through the stratosphere over the Equator and then affects the general circulation over the coming few months. Using my knowledge about how this was likely to affect the Northern Hemisphere Atmospheric Angular Momentum budget; I factored it into my forecasts. However, other developments can and do knock forecasts off course; major weather shifts over continents like Eurasia can develop much more quickly and entrenched cold or warmth there can have just a big an effect as sea-surface temperature anomalies. The near-record increase in Eurasian snow-cover over the last month is a case in point, indeed you cannot predict accurately what these sorts of situations will be like months in advance and do need to make updates when they happen and affect the basis of an earlier prediction of the season ahead.

@seaside 60 I will provide you with some of the reasoning underpinning my forecast for this coming Winter. Firstly you mention Arctic sea-ice, and it seems to be a contention that others on this Forum have that less pack-ice and a warmer Arctic encourage high-latitude blocking and weaker Westerlies around the periphery: A couple of points, firstly if the entire Arctic were substantially warmer the warmth of the low atmosphere would affect the middle troposphere too, raising thickness heights over the Arctic. The warmer temperature and higher pressure of the Arctic mid-troposphere would certainly reduce the strong temperature gradient between the Arctic interior and the periphery which, other things being equal, would weaken the Circumpolar Vortex and permit blocking-patterns to occur more frequently over the northern continents. However, where there is less/removed pack-ice locally this is more important than higher thickness values higher up because open water keeps such parts of the Arctic much warmer than they would otherwise be. Warm air expands and where the low atmosphere is markedly warmer with little change aloft this leads to markedly lower pressure- hence my clear scepticism that high-pressure could dominate over sub-Arctic waters where sea-surface temperatures this autumn have run up to 6C warmer than usual. This brings one, naturally, to the second point that if the periphery of the Arctic is warmer but the interior still gets very cold (certain to be the case by December) then higher-level thickness vales will still be low over the central Arctic but the extensive warmth of the sub-arctic will mean a warmer atmosphere and higher mid-tropospheric thickness values around the periphery of the Arctic- leading to increased baroclinicity, deeper depressions and stronger Westerlies along their southern flanks. Furthermore, a major source of fuel and energy for sub-polar depressions is the latent heat released when moisture fed into them from the south-west condenses as the warm-sector conveyors feeding into such depressions rises. Warmer seas over and south of the depression tracks furnish more moisture and more latent-heat release fuelling the depressions; ergo deeper depressions and stronger Westerlies. A third obvious point, too, is that if the seas to the north of Britain are warmer, any frigid Arctic air-masses that do travel south to Britain will be modified more by the warmer seas and so will be less cold on reaching Britain! Against the above, increased snow-cover over Russia and Scandinavia, as has recently been the case, increases the chances of cold weather coming from the east: Increased snow-cover over northern continents in early winter is a profound cooling influence because of the dramatic increase in surface albedo (reflectivity) of this whole region that results. Fresh powdery snow-cover reflects 80% of the Sun's heat whilst radiating strongly at terrestrial wavelengths, even given that the Sun is low in the sky in those regions at this time of year anyway. The strong surface cooling results in colder, denser air in the low atmosphere so surface pressure rises sharply as a strong cold-air anticyclone develops, the resulting subsidence in which keeps skies clear and thus further enhances strong seasonal net cooling leading to even lower temperatures and higher surface-pressure. Further east the extensive cooling eventually filters into the mid-troposphere decreasing thickness heights and leading to slightly lower pressure (the weak northerly airflow would bring even colder air at the surface and still maintains high surface pressure there despite lower thickness heights aloft). Anyway, the upshot of extensive Russian/Scandinavian snow-cover is a stronger Siberian High composed of colder air- and able to extend westwards even in the face of quite strong Westerlies coming in off the North Atlantic. A major control underpinning the weather we tend to get in Britain (and in all higher-latitude locations) in all seasons is the Law of Conservation of Angular Momentum and the tendency for the global atmosphere, as a whole, to rotate with the Earth itself around it's axis of rotation: In low latitudes and in the subtropics the atmosphere is continually gaining relative westerly momentum as a result of the tropical easterlies blowing in a direction opposite to the Earth's rotation and as these easterlies lose momentum to the Earth through frictional interaction with the underlying surface the atmosphere as a whole gains relative westerly momentum. It is this Westerly atmospheric angular momentum (AAM) that ultimately finds it's outlet in the Westerlies of higher latitudes that return this Westerly relative momentum to the Earth's surface- again through frictional interaction with the underlying surface. In very high latitudes, too, there are polar easterlies which also contribute to an increase in Westerly AAM through their frictional interaction with the underlying surface (though not by very much owing to their limited extent and being so close to the axis of the Earth's rotation) and the sink for this is also the mid- higher latitude Westerlies. Now, in the late autumn and winter as the subtropical lands and oceans cool down the increased surface pressure in the subtropical high-pressure belts that results leads to stronger NE Trade Winds, strong high-pressure over Russia and NW Canada in early winter also leads to easterlies on the southern flanks of these cold-air anticyclones and all these easterlies add quite a lot of Westerly AAM to the atmospheric general circulation through the frictional interaction of these extensive easterlies with the underlying surfaces. That demands a sizeable sink for this Westerly AAM and that naturally leads to the North Atlantic and North Pacific Oceans and implies strong Westerlies will force their way in towards Britain. This is fundamental physics. Now it is possible for the strong Westerlies there needs to be to counterbalance extensive lower and very high latitude easterlies to be resisted, possibly by very cold air over northern Europe, in which case the upper atmosphere continues to gain Westerly AAM and soon the Circumpolar Vortex becomes stronger: This reduces the flow of warm air aloft towards the Arctic, baroclinic gradients increase on the periphery of the Arctic and deeper depressions with stronger Westerlies soon result, relieving the atmospheric circulation of the accumulated Westerly AAM (and pushing back cold air that might be encroaching on the UK). Sometimes when there is very cold air over northern Europe this sink for Westerly AAM is pushed south into the Med (as deep depressions with attendant Westerlies are pushed into that region) but when sea-surface temperatures are warm north of Britain this is more likely to be pushed well to the north. This tends to lead to an increase in the Westerlies since they have to blow stronger when closer to the axis of the Earth's rotation in order to counter the effect of the lower latitude easterlies (think about see-saws and you'll appreciate why this is so!). You'll appreciate thus why I am less than sanguine about the potential for frequent spells of easterlies and northerlies reaching Britain, rather than south-westerlies, when sea-surface temperatures are warm going into winter just north of Britain. In addition to all this, we have the Quasi Biennial Oscillation (QBO) wind-pattern in the Equatorial Stratosphere. Thanks to some upset in the Northern Hemisphere Circulation earlier this year the winds at the 30 mb level high above the Equator averaged at over 10 metres per second from the west there (that is, in other words, a sizeable zone of persistent Westerly AAM being stored in an extensive region of the Equatorial Stratosphere) and at some point in the next few month this excess Westerly AAM will filter into the atmospheric circulation at higher northern latitudes and find it's way to the surface: This, of course, does not look good for the prospects for plenty of frigid winds of Russia come January. Of course, the global Westerly AAM Budget is not everything: Under certain extreme conditions strong high-pressure could dominate the sub-tropics, mid-latitudes and the Arctic with the sink for Westerly AAM being the effect of stronger Westerlies aloft that would result over the sub-tropics impacting the likes of the Himalayas and zones of strong subsidence at 20 to 30N bringing down westerly-moving air from aloft to result in extensive north-westerly (rather than north-easterly) Trade Winds at the surface in the subtropics, chiefly south-eastwards of stronger north-south ridges. Or the strong cold anticyclones over higher latitudes could lead to low-pressure in the stratosphere over high latitudes with the Westerly AAM being shunted upwards and stored there as a result (at least until the spring), with a small amount of Westerly AAM permanently lost through diffusion of the highest parts of the atmosphere to space (that latter situation would soon lead to the permanent slowing down of the Earth with the length of day increasing by a few milliseconds!). However, for anything like that to occur everywhere poleward of 30N would have to be frigid (preferably snow-covered) continents or frozen oceans: Unlikely to have occurred since the most severe phase of the last Ice Age! On a positive note we do have a weak La Nina- cool waters over the Equatorial Pacific weaken the Intertropical Convergence zone (ITCZ) locally through cooling the equatorial Pacific air significantly. This weakens, rather than strengthens, the NE Trade Winds further north and that implies the creation of less relative westerly AAM that requires a sink at higher latitudes (ergo Weaker Westerlies off the North Atlantic). A weaker phase of the Sunspot Cycle also helps. There is also a patch of the North Atlantic that is substantially colder than normal for the season, however it is too far west, in my view, to aid colder, more anticyclonic types near the UK. But I fear that the Westerly QBO, the warmth of sub-polar oceans (with the Arctic interior still getting very cold) and the normal course of increased NE Trade Winds, etc as the subtropics cool going into winter leading to a need for an outlet for increased Westerly AAM in higher latitudes will outweigh the effects of a weak Lá Nina, extensive Eurasian snow-cover and the (likely to vanish) anomalous warmth of the Arctic interior. I hope this helps.

The great Economist of the 20th Century, one John Maynard Keynes, once said "When the facts change I change my mind. What do you do Sir?". When the large-scale patterns of sea-surface temperature, stratospheric winds over the Equator, sea-ice and Northern Hemisphere snow-cover that underpin a seasonal forecast change in unexpected ways (and beyond that anticipated from normal seasonal changes), that is the time to provide an update on the basis of the new developments. The folly would be to persist in a forecast based on parameters that are no longer true (and not now going to come true). Such a forecast is even more likely to be wrong. For example, the big increase in snow-cover across Russia during October was surprising, and could not have been predicted on the basis of what the the various large-scale parameters were at the beginning of last month. Another point, when all the various model runs show something different afoot covering the beginning of the forecast period, then as we approach the start of the forecast period it is eminently sensible to factor this into the updated forecast that would be required.

Looking the the outlook charts and, having revised my prediction for November made back at the start of October, I will plump for a CET of 6.8C if I may (and if I may add I think there will be on average 90 mm rainfall over England and Wales as a whole).

WINTER 2016-17 UPDATE: In the light of certain recent developments, in particular the fact that most forecast models for the next month seem to point to there being colder and drier conditions in November, Arctic sea-ice extent running at an all-time record low and the big increase in Eurasian snow-cover seen during October 2016 I have decided to post an update from my earlier preliminary prediction: I am not expecting November 2016 to be as mild and wet as earlier forecast and I expect there to be notable spells with winds from a northerly quarter early in the month: This will bring much colder conditions to the UK as the air will have originated from well within the Arctic Circle and I expect the first snowfall of the winter to affect much of lowland Scotland and NE England (along with higher ground further south), though I am not expecting it to be cold enough for any snow that falls to lie for more than a few hours anywhere below 300 metres above sea level (except in northernmost Scotland). In the clearer night skies following this northerly incursion the first widespread air-frosts of the season will affect Britain, with air-frost expected even in the lowlands of Devon and Cornwall; lowland Scotland and northern England (away from the coast) can expect minima of -3C or colder. In between these cold northerly outbreaks there will be milder, moist south-westerlies but with high-pressure not far from SW Britain rainfall amounts will be low (except in NW Scotland). Late November will see more unsettled weather as atmospheric temperature gradients (baroclinic zones) intensify over the far North Atlantic as Greenland and the Arctic become very cold and the increase in NE Trade Winds (in response to seasonal cooling over sub-tropical continents) increases the rate at which westerly AAM enters the general atmospheric circulation of the Northern Hemisphere) and demands a corresponding greater sink for this westerly AAM to counter-balance it (through an increase in intensity of higher-latitude depressions and attendant Westerlies). However, with Arctic sea-ice at exceptionally low levels, the extent of low-level warmth resulting could affect mid-atmospheric thickness heights over the Arctic interior, thus ensuring that the baroclinic gradients on the periphery do not increase to the level of intensity normally expected by late November; this would reduce the intensity of higher-latitude depressions. The change to a weak Lá Nina and weaker phase of the Solar Cycle also lends support to weaker Westerlies; the unusually rapid increase in snow-cover over Eurasia would support a stronger Siberian High developing and this could extend west wards to bring much colder and drier conditions to western Europe. Against all this however the QBO was over 10 metres/second, westerly at 30 mb in September (exceptionally "Westerly") and that influence would serve to considerably strengthen the Westerlies coming over the North Atlantic over coming months, also warmer than normal sea-surface temperatures just north of Britain do not encourage high-pressure to form locally over those seas, but rather to provide latent-heat fuel for depressions moving into the area. On balance, late November will be wetter and windier but there will also be at least one cold settled spells with widespread night frosts and (possibly freezing) fog forming and persisting over favoured locations in the Midlands and Yorkshire. Revised CET Prediction for November 2016: 7.0C; Rainfall total over England and Wales: 85 mm. November 2016 Scotland: Mean temperature for lowlands: 5.5C, Rainfall: 130 mm In December I am still expecting a general change to wetter and stormier conditions based on the current Quasi Biennial Oscillation being strongly Westerly and the warmth of the far NE Atlantic. However, the patch of anomalously cold water in the mid North Atlantic (currently up to 3C colder than the late October norm at 50N and 25W) will help cause higher pressure to form over and SW of this area and there will be a southwards displacement of the southern part of the circumpolar Vortex over the NE Atlantic coming into Europe as a result. With Europe getting cold by December and with sea-surface temperatures (currently) above normal in the Med this favours more (and deeper) depressions moving into the north-western Med by then. Meanwhile, even with Arctic sea-ice as anomalously low as it is (currently) the central Arctic and Greenland will still be very cold by December and the increased baroclinicity between these areas and a warmer-than-normal far North Atlantic can only serve to increase the intensity of depressions moving north-east along a line from southernmost Greenland, over Iceland and towards Spitzbergen. Further east the increased early winter snow-cover will be helping the Siberian high develop to greater intensity and this is likely to nose westwards into the gap between the north Mediterranean and Iceland-Greenland Sea storm tracks; in other words frigid high-pressure is liable to nose westwards from Russia over central northern Europe. It remains my contention that the Westerly QBO and the need for a strong sink for Westerly AAM (caused by stronger NE Trade Winds by December and strengthened more by the QBO) will not allow this cold high-pressure area to get much westwards of Denmark so that most of December will be relatively mild, wet and windy. However, the cold Eurasian Anticyclone is certain to win out earlier in December, at least for England and Wales (before the circumpolar Vortex reaches maximum strength) to bring a week of very cold settled weather during which severe night frosts (widely down to -5C over the lowlands) and with freezing fog over the Midlands, Yorkshire and the Thames Valley. Scotland and Northern Ireland will remain under the influence of (by then) deep depressions moving north-eastwards over Iceland and will be wet and windy throughout the month. However, the cold patch in the mid North Atlantic will encourage local high-pressure there at times and, consequently, colder spells with west or NW winds will bring short cold snaps with snow-showers to Scotland and widespread frost will still occur here in the clear night or two following these cold NW incursions. Gales and high rainfall are likely to feature heavily in the North West and western Scotland in late December. Overall December 2016 CET: 5.0C; England and Wales Rainfall: 100 mm December 2016 Scotland Mean temp: 4.5C, Rainfall: 140 mm. My predictions for January and February 2017 remain much as above. I will reduce the CET predicted for January to 4.5C and amend monthly rainfall for England and Wales to 90 mm; I will also reduce Scotland's predicted mean temperature for January 2017 to 4C because I now believe there is a likelihood of at least one very cold south-easterly spell from Russia via central Europe that will affect the entire country. February 2017's prediction remains as above.

Could it be that we have something colder on the cards for November 2016? Looking at the various predictions, such as from the Met.Office, there are indications we could have cold north/north-westerly airstreams bringing a real foretaste of winter and the first sharp air-frosts nationwide during the coming month. For my part, I predicted (reluctantly) a mild, wet November largely based on the warmth of the far NE Atlantic and the QBO remaining in a Westerly phase; but it is nice to see a prospect of crisp frosty mornings and (certainly where I live) the first snows of winter on the highest fells. Much more preferable to November last year!

I am also open to recommendations for other long-term prediction sites: I know they are not all 100% reliable, but if a large number of diverse models are all pointing in the same direction it gives one confidence to make more certain predictions, particularly for the early part of a long-range (monthly/seasonal) outlook. I am sure that would be beneficial for us all.

@Nick L, Perhaps the charts they have on display (that one can access via weathercharts.org) are GFS ones because that is what is written underneath each of the displayed charts. I understand that Wetterzentrale is indeed a major German weather site that uses a variety of models, it is just that the weather charts (of Wetterzentrale) that I refer to are those that one can access through weathercharts.org. Likewise the Meteociel charts. I hope that clarifies the issue of what forecast surface-pressure charts I tend to look at.

You can see one of them here: http://www.weathercharts.org/wetterzentrale-t120-t384.htm The Wetterzentrale pressure charts are GFS.