Winter 2016/2017: Preliminary Prediction

[Walsall Wood Snow]

3 hours ago, I remember Atlantic 252 said:

I only know basics but agree with that, everyone I have spoken to knows our winters are not what they used to be 17+ years ago, not one person disagrees, except people on netweather that don't want to admit it

Yeah you're right 17 years ago (1999/2000) we had a mild Winter. Even 18 and 19 years ago we had mild Winters (1998/99 & 1997/98). In fact with the exceptions of 1990/91, 1995/96 and 1996/97 (though 1993/94 was coldish, but more so in late Autumn) most of the 90's Winters were at best average to mild and not especially snowy, despite your insistence otherwise. Whereas in the period 2008 to 2013 (2011/12 excepted, but even that Winter had a cold spell in early February) we had some of the best Winters this country has experienced since the run of cold Winters from the late 70s to the late 80s. With 2009/10 been the coldest since 1978/79, November 2010 been the coldest since 1993 (possibly even 1985, though I'm not sure about this), December 2010 been the coldest since 1890! and March 2013 been the coldest since 1962. Yes we've have had a run of mild Winters since then but that's only 3 years (it may be longer or about to end) and has been nothing unusual as we have had other such periods in the bulk of the 00s, the late 90's, late 80s, the bulk of the 70s and going back before then the bulk of the early 20th century until the beginning of the 1940s, when we went into a period when cold Winters had become more common more or less (with the early to mid 70s excepted as I stated above) right up until the late 80s. If somebody from anywhere from the dawn of the 20th century to the 30s somehow travelled in time to post Winter 2012/13 to right now they wouldn't find the Winters since then particularly unusual to the Winters they were accustomed to during their own time period (ok Winter 2013/14 and December 2015 might be but that's because they were and will likely remain so, but so we're December 2010 and March 2013). If we were living back then though as cold fans we would find the average Winter just as frustrating for getting snow then as we have over the last 3 years. I don't know whether this Winter will be cold or not but I'm sure we'll get another one soon enough, so all this talk about Winters not been what they used to be is completely relative and in fact they are just like they used to be during certain periods. The only question is what type of past Winter will this Winter be like?

 

Edited October 28, 2016 by Walsall Wood Snow

[Matthew.]

I remember the late 90's early-mid 2000,s winter theme of the 2 day arctic snap. There were many of these arctic snaps during this period. I remember the one from January 30th 2003 very well. I wonder if weather-history has a video!

[Weather-history]

26 minutes ago, Walsall Wood Snow said:

Yeah you're right 17 years ago (1999/2000) we had a mild Winter. Even 18 and 19 years ago we had mild Winters (1998/99 & 1997/98). In fact with the exceptions of 1990/91, 1995/96 and 1996/97 (though 1993/94 was coldish, but more so in late Autumn) most of the 90's Winters were at best average to mild and not especially snowy, despite your insistence otherwise. Whereas in the period 2008 to 2013 (2011/12 excepted, but even that Winter had a cold spell in early February) we had some of the best Winters this country has experienced since the run of cold Winters from the late 70s to the late 80s. With 2009/10 been the coldest since 1978/79, November 2010 been the coldest since 1993 (possibly even 1985, though I'm not sure about this), December 2010 been the coldest since 1890! and March 2013 been the coldest since 1962. Yes we've have had a run of mild Winters since then but that's only 3 years (it may be longer or about to end) and has been nothing unusual as we have had other such periods in the bulk of the 00s, the late 90's, late 80s, the bulk of the 70s and going back before then the bulk of the early 20th century until the beginning of the 1940s, when we went into a period when cold Winters had become more common more or less (with the early to mid 70s excepted as I stated above) right up until the late 80s. If somebody from anywhere from the dawn of the 20th century to the 30s somehow travelled in time to post Winter 2012/13 to right now they wouldn't find the Winters since then particularly unusual to the Winters they were accustomed to during their own time period (ok Winter 2013/14 and December 2015 might be but that's because they were and will likely remain so, but so we're December 2010 and March 2013). If we were living back then though as cold fans we would find the average Winter just as frustrating for getting snow then as we have over the last 3 years. I don't know whether this Winter will be cold or not but I'm sure we'll get another one soon enough, so all this talk about Winters not been what they used to be is completely relative and in fact they are just like they used to be during certain periods. The only question is what type of past Winter will this Winter be like?

 

Yes, the winters 1987-88 to 2007-08 were for the most part were less than brilliant. The Manchester Index from 1996-97 to 2007-08 never got above 80 and for most of the time was in the 40s. The Manchester Winter Index has got above 80, in 5 winters since then.

Winters 1991-92 and 1992-93 were not that particularly mild but they were virtually snowless. For my location, I saw hardly any snow after that Feb 1991 cold spell to November 1993. The wintriest spell from February 1997 to late December 2000 was mid April 1998! 

9th March-8th April 2013 CET was colder than any month from 1987-88 to 2007-08 apart from February 1991 and December 1995.

[Weather-history]

15 minutes ago, Matthew Wilson said:

I remember the late 90's early-mid 2000,s winter theme of the 2 day arctic snap. There were many of these arctic snaps during this period. I remember the one from January 30th 2003 very well. I wonder if weather-history has a video!

I have hundreds of BBC weather forecasts from January 1993 to February 2011 uploaded on Youtube

 

[Matthew.]

14 minutes ago, Weather-history said:

I have hundreds of BBC weather forecasts from January 1993 to February 2011 uploaded on Youtube

 

Thank you. Living on the east coast at the time these events had a memorable impact but this one in particular and affected a much larger area. I can still picture that blue cold front sweeping south bringing a true northerly and heavy snow in just a few hours. I was looking forward to it 3 days prior to the event from keeping an eye on the forecast at the time.

Edit:Thanks for the news report aswell.

Edited October 28, 2016 by Matthew Wilson

[BLAST FROM THE PAST]

Ok want to whet the appetite.  

Dec - below norm with potent blasts from north.

Jan - similar theme but potential extremely potent easterly blast.  Thus well below

Feb - like Dec but strengthening sun.....still nice potential....average

 

BFTP

 

 

[iapennell]

23 hours ago, Nick L said:

No they're not, they have all the major models. WZ is simply a hosting site where you can view all the models, much like Netweather, much like Meteociel.

Wetterzentrale means "Weather Central" in German. A central point where you can assess all models.

@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.

[iapennell]

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.

[WillinGlossop]

16 hours ago, BLAST FROM THE PAST said:

Ok want to whet the appetite.  

Dec - below norm with potent blasts from north.

Jan - similar theme but potential extremely potent easterly blast.  Thus well below

Feb - like Dec but strengthening sun.....still nice potential....average

 

BFTP

 

 

If that were to happen id be buried in snow.....❄️❄️ Eventhough last winter was pants in most places we did manage a fair few decent snowfalls....even in april where we went from one day having a bbq 21c in garden three days later a covering of snow.... so a nov/dec 2010 or march 2013 would be welcome.... 

[iapennell]

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.   

Edited October 29, 2016 by iapennell

[Matthew.]

Thanks for your insight Ian So away from Scotland pretty average conditions temperature wise and maybe slightly wetter than average overall. This would bring us the coldest winter since 2014/15 maybe even 2012/13. Snowy snaps limited but the main difference I see is the potential for more HP than 2014/15 so fog/frost a bit more likely. This sounds like what I'm expecting really. So November first then-average rainfall-average temps for England. 

[ditch]

Love Netweather and the predictions made by others. It has been a very benign Autumn and continues to be so and foresee an old fashioned November with frost and fog the main theme during the coming weeks. I have no idea what will follow into December but do hope for a colder than average winter with a least 3 or more national wide snow events, which I will be more than happy with.

 

 

[bluearmy]

I think you're beginning to get there Ian although second half Jan and into Feb are much too far away imo to make any kind of informed punt

The PFJ could be well south of where one might expect it come any increase in the westerlies and as such could allow the Siberian ridge to extend its influence further west than you expect. 

Plenty of time for many flies to arrive in the ointment though before the background  pattern is established.

[Radiating Dendrite]

Best of luck Ian.

I think the fact that you are already amending your forecast says it all though. 

[Matthew.]

An interesting article on how Solar/geomagnetic influences might change the winter for one way or the other: http://www.bbc.co.uk/blogs/paulhudson/2010/03/blame-the-jet-stream-for-the-c.shtml

[Seasonality]

On 28/10/2016 at 23:39, BLAST FROM THE PAST said:

Ok want to whet the appetite.  

Dec - below norm with potent blasts from north.

Jan - similar theme but potential extremely potent easterly blast.  Thus well below

Feb - like Dec but strengthening sun.....still nice potential....average

 

BFTP

 

 

Oh you tease BFTP. Coming from you though I'm inclined to believe it.

[Barry12]

Met Office seem to disagree with this forecast, but we'll see whos closer to the mark come March 1st.

Best of luck iapennell

Edited November 1, 2016 by Barry95

[seaside 60]

On 10/10/2016 at 08:20, seaside 60 said:

Thanks for your time in this expansive forecast.

Always a pleasure to read.

Can you tell me against yours and Gavin's ideas, why the MO are hinting at what appears to be quite consistently pointing towards high pressure to the north and lower pressure to the south.

Its a constructive question, does the EC 42/ Glosc see some thing we/you don't or is it just numbers which are likely to change.

To be fair they have been pretty good in recent times.

I asked this question over 3 weeks ago and you must of missed it.
Its still relevant and after the latest 3 month outlook from the MO I am just trying to understand why until recently you appear to be going against their ideas.
Particualy your idea that record low  Arctic sea ice and warmer waters in the N Alantic and beyond point to more pressure gradient for low pressure systems rather than high pressure which everyone else mentions.
In no means is this a criticism because you may well be right, even if you have tweaked your forecast the other day. 
I greatly appreciate the efforts of your forecasts based on your knowledge but can not get my head round some of your base ideas.
Thanks for your time in replying.
 

[BLAST FROM THE PAST]

On 30/10/2016 at 13:25, Seasonality said:

Oh you tease BFTP. Coming from you though I'm inclined to believe it.

Too kind my friend.....but I have hope.

 

BFTP

[iapennell]

On 10/30/2016 at 04:42, Radiating Dendrite said:

Best of luck Ian.

I think the fact that you are already amending your forecast says it all though. 

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.

 

[iapennell]

On 11/1/2016 at 17:31, seaside 60 said:

I asked this question over 3 weeks ago and you must of missed it.
Its still relevant and after the latest 3 month outlook from the MO I am just trying to understand why until recently you appear to be going against their ideas.
Particualy your idea that record low  Arctic sea ice and warmer waters in the N Alantic and beyond point to more pressure gradient for low pressure systems rather than high pressure which everyone else mentions.
In no means is this a criticism because you may well be right, even if you have tweaked your forecast the other day. 
I greatly appreciate the efforts of your forecasts based on your knowledge but can not get my head round some of your base ideas.
Thanks for your time in replying.
 

@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.

 

 

[Radiating Dendrite]

1 hour ago, iapennell said:

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.

 

Yes; I understand this completely. My problem is it surely becomes nothing more than a weekly forecast when it has to be updated on a weekly timescale due to unforseen changes. 

I admire anyone who gives a seasonal forecast ago but the problem with most is they go into far too much detail. When the METO will only issue probability forecasts for a season ahead, how can an amateur going into much greater detail be taken with more than a pinch of salt.

Would it not be best to present a seasonal forecast as simply as (as an example):

DEC - Warmer than Average and wetter than average. 

Jan - Colder and drier

Feb - near average and wet

Think you would have more of a fighting chance and require fewer changes. 

Edited November 2, 2016 by Radiating Dendrite

[Ice Day]

OK, time to nail my colours to the mast.  Here's my thoughts on Winter 2016/17 (I'm completely unqualified but very keen!!!)

November - Temps slightly below average along with lower than average rainfall.  No UK notable snow events

December - First half of the month, above average temps in the south, average in the north along with average rainfall.  Second half of December will bring a rapid cool down with significant snowfall in Scotland and Northern England (lump on a white Christmas in these areas!).  Below average temps in the south but mainly dry.

January - A significant nationwide snow event will take place in the first half of the month emanating from a northerly that swings north easterly finally around to a full blown beasterly.  Second half of the month will be colder than average but dry.

February - Starts off benign but becomes a very stormy month (the Atlantic has to kick in eventually).  Above average temps and rainfall.

 

What can go wrong?

 

[Hocus Pocus]

Surely the problem Ian is issuing a forecast in October when all the relevant players have yet to show their hand?

[iapennell]

19 hours ago, Radiating Dendrite said:

Yes; I understand this completely. My problem is it surely becomes nothing more than a weekly forecast when it has to be updated on a weekly timescale due to unforseen changes. 

I admire anyone who gives a seasonal forecast ago but the problem with most is they go into far too much detail. When the METO will only issue probability forecasts for a season ahead, how can an amateur going into much greater detail be taken with more than a pinch of salt.

Would it not be best to present a seasonal forecast as simply as (as an example):

DEC - Warmer than Average and wetter than average. 

Jan - Colder and drier

Feb - near average and wet

Think you would have more of a fighting chance and require fewer changes. 

@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.