Glacier Point

With uncertainty over the Arctic Oscillation, this is a very difficult call and guesses could be spectacularly wrong. I'm going for an underying -ve NAO pattern, which should become increasingly evident through the mid to later part of May, the first week very unsettled but essentially average or just above. Overall an average or just below month, 11.1 C for me please. GP

With TWO's CET currently at 5.42 and Metcheck 6.1, the first third of the month has been well below average, on a par with the coolest Aprils in the last 60 years. Another northerly looks a distinct possibility next week, whilst I see the factors leading to more high latitude blocking to increase in probability as we approach the last third of the month and into May. March's NAO was -1.4, and if anything April could be more negative. So perhaps we could see one of if not the coldest April in the last 60 years ? GP

or the Greenland High southwards !

Todays SSTA plot continues a recent trend for upwelling of cold water off the western USA from Washington down to California: http://weather.unisys.com/archive/sst/sst_anom-060312.gif http://weather.unisys.com/archive/sst/sst_anom-060326.gif http://weather.unisys.com/archive/sst/sst_anom-060402.gif http://weather.unisys.com/surface/sst_anom.html This is hugely significant in terms of influencing our weather as it sets up a probable big amplification of the Jet, its effects likely to be felt by the UK into early May. Cold anomalies off the western USA set up a large mean trough into the western USA with a pronounced downstream ridge over the Central Plains. With cold pooling off the Gulf Coast and a -ve NAO in place, high pressure will dominate to the west of Greenland and a large mean trough will form over the eastern USA and into the western Atlantic. A large downstream ridge will develop mid-Atlantic, which, with blocking over Greenland, will result in a northerly airflow for the UK, particularly with a cold SSTA to the north of Scandinavia. The location of the ridge will be crucial in dictating just how cool things will get, but I would suggest that the first half of May will be very cool, perhaps even one of coldest this Century, coming on the back of a decidely interesting start to the month from the deepest NAO reading I've recorded thus far in late March. Not great for the garden at all, so don't be lured into putting those bedding plants out just yet. Still, if it gives days like this with crisp, clean air and plenty of sunshine feeling warm out of the wind, not too bad IMO. GP

Yes I see where you're coming from, but the sheer size and location of the couplet formed across the cold anomaly off the eastern Seaboard, the cold extratropical band and the warm northern anomaly is likely to overwhelm any impact of anomalies close to Greenland. I have come across research suggesting SSTA in the extra tropics to be far more potent in terms of their impact on Rossby Waves compared to those in high latitudes, something I would tend to endorse. One also has to consider where the jet will be placed in such as set up. At present, the weak La Nina event allied to the strongly -ve NAO developing teleconnects to low pressure over Iberia and the western Atlantic, with the warm anomaly favouring mean positive height anomalies towards Iceland and NE Canada, something like this but with pressure higher over the UK .... So I would suggest mean April / May jet flow to be totally deflected southwards of the UK with lows desperately trying to edge in from the SW but never quite making it and a generally north to NW'ly flow setting up. GP

Wow ! http://weather.unisys.com/surface/sst_anom.html biggest -ve NAO on its way for early May. Just look at that extratropical banding cold anomaly. With the Pacific signal quiet, this I think will strongly favour cool conditions for the UK and western Europe. GP

I haven't got the time for a thorough Spring forecast although with only two months left and a -ve NAO / neutral pacific signal 'in the bank' for until at least early May, I'd punt a below average Spring on this basis alone, similar to 1996. As for the Summer, I'd like to give it a go time permitting as the Summer presents different forecasting challenges - you need to look south as well as north.

Thanks for your LRF review Ian. Although it had its downsides, the winter of 2005/6 went some way to re-define the even larger teapot and gave us some cause for optimism in the future. Here is my review of the Long Range Forecast I made back in November (link here: http://www.net-weather.co.uk/forum/index.p...ndpost&p=487441) which draws out the main pluses and negative points, and which provides some possible pointers for next winter. Overall I would draw a large positive from the trend away from the string of above average winters experienced over the last decade, a call made by my and many other LRFs. Whilst it might seem quite obvious now, the LRFs that called a below average winter were bold in the face of month after month, year after year of above average temperatures. Also positives of the LRF were the increased duration of the winter, dryness, strong Pacific Jet, displaced polar vortex and the CET for December and February called for. Winter Summary 500 hPa anomaly MSLP anomaly surface temp. anomaly As a major negative, I was totally wrong with January and the fact remains that this month IS the winter month for many where we see our best chance of widespread snow and once again it failed to materialise. Other negatives were the importance attached to the Madden Julien Oscillation (a forecasting error as you cant have a strong easterly phase Pacific Jet with this), and indeed the Quasi-Biennial Oscillation's (QBO) exclusion of blocking over Greenland. Summer warmth - winter cold One of the key factors influencing my winter forecast was the approaching solar minima. Many had argued that this was irrelevant and that the overall warming trend experienced over the last decade was the key determinant for our winter. A sizeable pool of cold air did however develop over the Arctic Ocean, Siberia and Greenland. This cold made its presence felt as far south as Iberia as well as much of Europe and this must be regarded as a near miss as far as the south of England is concerned. Notably the cold air over continental North America was lacking. I would cite this distribution (if you push a balloon it distorts elsewhere) and reduced incoming radiation as the key causes - something which augers well for next year - the low point of the solar cycle. There will have developed a sizeable cold pool next winter - but we must note that the distribution of cold air must once again favour the eastern hemisphere. Back in November I identified a combination of an active hurricane season (increased tropical Atlantic convection), neutral El Nino Southern Oscillation (ENSO) conditions allied to a warm September as possible signals of an impending reversal in the monthly warming trend. I think the dramatic shift in patterns during November which took an above average first half of the month to a below average second half of the month in some way may be attributed to this, as can in part the following December pattern. So if we arrive in October with ENSO neutral (as they may well be) conditions, and a warm September behind us, take the tip, the cold will not be far away. The shift to weak La Nina conditions may however have promoted alterations in the Pacific and jet patterns over North America this time around. The NAO Many LRFs were predicated on a -ve North Atlantic Oscillation (NAO), mine included. Whilst neutral or -ve conditions were observed through a good part of the winter, they were no where near as negative as they needed to be in order to sustain prolonged cold. This depends somewhat on your measure but I use the CDC (Sea Surface Temperature Anomaly) (SSTA) definition. http://www.cdc.noaa.gov/Correlation/nao.data http://www.cdc.noaa.gov/people/gary.bates/tele/nao.gif Only during late February did we see prolonged -ve phase develop and sure enough it did what it says on the tin delivering a well below average end of February and start to March. The direct cause of a lack of a prolonged -ve NAO during the core of the winter (January had a recorded value in excess of +1) was for me the SSTAs in the North Atlantic. Whilst many forecasts predicted the warm pooling to move northwards during December and January (thereby bring about the necessary conditions for a -ve NAO), it took its time and largely stayed put NE of Newfoundland: http://weather.unisys.com/archive/sst/sst_anom-051218.gif Finally when it did move north with the corresponding development of a cold SSTA in the sub-topical Atlantic, the jet finally displaced southwards and we were treated to a true Greenland High on the back of an easterly. http://weather.unisys.com/archive/sst/sst_anom-060205.gif http://weather.unisys.com/archive/sst/sst_anom-060219.gif http://weather.unisys.com/archive/sst/sst_anom-060312.gif This for me was clear evidence that given the right SSTA, a warm Atlantic can deliver a cold pattern. The QBO and Pacific Jet Make no mistake, the reason in my book why we did not get a severe winter is the QBO. http://www.cdc.noaa.gov/Correlation/qbo.data This very high altitude zonal wind is regarded by many metreologists as a key measure of the likely strength and positioning of the Pacific Jet. Throughout the key part of the winter, the QBO was in a deeply -ve (easterly) phase with record November and very high December values experienced. This was highly predictable and my LRF did acknowledge this. However, I made the mistake of assuming that a strongly -ve QBO and -ve NAO were not mutually exclusive as there was some evidence from reanalysis charts and analogue years such as 1962/3 suggested that the two could occur together. I won't be making that mistake again. Basically a strong Pacific Jet (especially the -ve phase) prevents pressure from building over Greenland, in other words it works against the -ve NAO and as the Pacific is twice the size of the Atlantic, the odds were stacked against the NAO developing. I also suspect that the strong Pacific Jet was a factor in preventing the SSTA in the Atlantic from moving as anticipated. It wasn't until the QBO relented in February that the Pacific North America pattern entered a -ve state which allowed the jet stream to pump storms over the Newfoundland area disrupting the sea surface and unshackling the warm anomaly and allowing the -ve NAO pattern to take over. For next winter we are most unlikely to have a -ve QBO, rather a neutral or developing +ve (westerly) phase based on the evidence of the cycle. Find of the winter must be the East Pacific Oscillation (EPO) and I must thank Steve Murr for pointing in the direction of EPO as I believe has been an excellent pointer this winter for the Pacific to relent and the North Atlantic to take over. All of our cold snaps more or less correlate to neutral / negative phases of the EPO. http://www.cdc.noaa.gov/people/gary.bates/tele/epo.gif The long range models Hats off the UKMET for their seasonal forecast, and indeed some of the other long range outputs for correctly punting a cold but not excessively cold and dry winter. We should note however that the numerical models generally got the beginning (cold November/December) wrong and the (cold dry) end right. Just a note on the UKMET - their method used the NAO statistical inference rather than numerical models. The NAO was just within the forecasts margin for error whilst the original forecast actually resembled their numerical model output - I think they hedged their bets. If next winter the numerical models and any other statistical forecast go for greater cold or warmth, we should make full use of them. Whilst on the subject of modelling, the shorter range stuff has been pretty dire with dramatic changes occurring in the t72 range across all models. Clearly the models struggle with displaced jet flows where short wave errors can have dramatic impacts in the near time scale. I'm loathe to single out one model as being particularly poor, but the operational GFS was throughout the post Christmas period and it clearly doesn't handle blocking over Greenland at all well. The ECMWF whilst poor at times was for me the model of the winter, and it can put the award on its mantle piece next to the Summer award. A post even larger teapot ? Perhaps by far the intriguing aspect of the winter was the exceptionally warm pole. I believe that this is a direct result of the last 25 or so years of forced anthropogenic warming, perhaps coinciding with a natural warming cycle. The planetary thermal balance is maintained through heat exchange to the poles where it is eventually lost to space. Lots of warming will eventually mean warm poles and I think we are beginning to see this trend emerging. Warm air in the troposphere will warm the stratosphere at the tropopause. Continued warming will I think lead to a warmed lower stratosphere and upper troposphere which because of the degree of warming will be long lived. Warm air aloft at high latitude leads to above average geopotential height anomalies, in effect high latitude blocking. This is therefore likely to be manifested in a -ve Arctic Oscillation for winters to come, providing much of the key ingredients for cold to develop at mid latitudes, especially with a solar minima. The almost unprecedented warming should however make the use of analogues less meaningful however. So as we leave this Winter and look forward to some welcome Summer warmth, we anticpate the QBO and Pacific as being less likely to interfer next time round, the AO to be -ve and with even less incoming radiation, the prospects for the Winter of 2006/7 look at this stage to be even better. Much however can and will change but we look forward having achieved much and with so much more to come.. GP

I'm going for a strongly -ve NAO month with alternating SW'ly and N'ly flow giving a marginally below average month at 7.9. Watch out for the snow showers and frosts late month to bring the prediction home ! GP

My reading of the current SSTA is of a quite strong mean pressure differential north to south in the Atlantic: http://weather.unisys.com/surface/sst_anom.html this is the strongest it's been all year which would force low pressure systems tracking off the USA to dive south-east across the Atlantic. This, with the seemingly always -ve AO, could deliver another phase of high latitude blocking late April early May. There was a brief spell when the SSTA in the western Pacific varied enough to suggest the development of a Bartlet mid to late April, but this quickly disappeared and I think another easterly late April is the inference from the oceans of the northern hemisphere. http://weather.unisys.com/archive/sst/sst_anom-060212.gif GP

Met Office / Beeb spectacularly wrong today with their temps... Max today 1.2, predicted 3 - 4 C, falling rapidly now under heavy cloud cover.

Evening all. Whilst next Thursday onwards looks increasingly interesting, particularly with the UKMO and ECMWF outputs placing the low to the east, my thoughts turn to the next 10 - 14 days when the real deal could materialise. Key to this is the Madden Julien Oscillation (MJO), a tropical wave which traverses the globe during neutral phases of El Nino Southern Oscillation. Some of the LRFs picked out the second week of December as the first real date for winter and the latest MJO forecast ties in nicely with this: http://www.cpc.ncep.noaa.gov/products/prec...ink/MJO/ewp.gif This shows the MJO moving from the eastern Pacific across central America and into the tropical Atlantic during the first-second weeks of December. Whilst this is a tropical feature, the impacts may be felt afar and this is likely to cause a number of events which will be felt by us. The first is the bifurcation of the Pacific Jet off the west coast of America with subsequent flattening of the jet. To go from an amplified flow such as experienced now: http://wxmaps.org/pix/hemi.jet.html ....to a flattened jet will have severe implications for an unstable downstream jet over western Europe, probably resulting in greater meridional flow, and with the current trend, greater chance of the second northerly attack followed by a milder phase mid to late December as the tropical instability pushes the Azores high NW towards the UK. One to watch. GP

Rolling back the years….. For the first time in a decade we have a coming together of a range of factors to bring about a cold Winter. Crucially, many of the problems which have floored promising previous winter synoptic (such as warm seas around Iceland) are now missing. Against this, we have to reconcile the huge uncertainty of an almost unprecedented warming trend. That is the conundrum that is the 2005/06 winter outlook. Back in 1990, had we been confronted with positive signals from Sea Surface Temperature Anomalies (SSTAs), increased tropical convection (and hurricane activity), an approaching low point of the solar cycle and an omnipresent Greenland High, it would have been a 'no-brainer' -the overwhelming view would be that the coming winter would have been well below average. The problem is that we have endured over fifteen years since the last widespread snowfall with only 1995/6 reminding us what winter can be like. Right now we stack up the above average months like a deck of cards. So, can the even larger teapot deliver when, for perhaps the first time in years, many of the key factors for cold are in probability ? Negatives Warming trend 2005 looks set to go down as the second warmest global year and perhaps the warmest ever hemispheric year. This is very much in line with the UKMO forecast which correctly predicted the warming based primarily on El-Nino Southern Oscillation (ENSO), anthropogenic forcing (greenhouse gases) and an absence of other factors such as volcanic activity. This warming is very much in line with the weather we have experienced this year over the UK with an impressive run of anomalously warm months stretching back into last year. This autumn threatens to be the warmest ever following near record breaking values for September and October in the UK and north-west Europe. Analysis of the warming trend reveals that the North-west European autumn is where the overall warming trend is felt: http://www.ncdc.noaa.gov/img/climate/resea...1979-fal-pg.gif …showing significant warm anomalies over Greenland, NE Canada and North-west Europe. It should have come as no surprise when, during the first week of September we recorded an above normal temperature coupled with a strong +ve North Atlantic Oscillation (NAO) index, the remainder of the Autumn turned out the way it has - being dominated by high pressure to our south and east with a run of seemingly endless southerlies. Plotting a simple straight line trend infers that following the warmest Autumn, at the height of a sustained warming trend, December and the following months are ordinarily strongly likely to follow suite. Any hope of cold weather must be 'bomb-proof' as this warming trend is likely to exploit any weakness in cold weather patterns. Snow cover and Sea Ice Some forecasters have used summer snow cover across Eurasia as a signal for the forthcoming winter based on the theory of a positive climatic feedback pattern. On this assumption, the lowly levels of snow cover recorded this Summer are reflective of the previous warming trends and infer strongly a lack of cold air pooling and the associated cold surface pressures over Eurasia. This would point towards a mobile Atlantic weather pattern and mild winter for the UK and Europe. Comparing 2005 with the 1967 - 2005 average reveals that like most of the last 10 yrs, we are between 5 and 10% down on the average. However, this should only be seen as one indicator as there have been below average years (1986 and 1990) which still produced colder than average winters. The amount of accumulated snow is also an important factor in determining the extent of cold air pooling over the pole. Less snow generally, but not always, equates to less severe cold and by implication we can expect less cold weather related to a weaker polar cell. The lack of cold air was one factor in mitigating considerably the effects of an easterly wind last Winter. A current tour of the northern hemisphere reveals that we remain warmer than normal: Numerical and dynamic models Most of the numerical seasonal forecast models have indicated a continuation of the warming trend into December, with some but not all going for something colder late January into February: http://www.met-office.gov.uk/research/seas...gle_terce2.html http://iri.columbia.edu/climate/forecast/n...06_Eur_temp.htm http://ecpc.ucsd.edu/projects/GSM_home_dat....ano_global.gif Whilst these model outputs tend to vary somewhat erratically, the overall consensus is of a milder, drier winter, possibly with a cold February repeating the pattern of last Winter. Unknown impact of warming Whilst there have been warm Autumns followed by cold Winters, the scale of the warming this time round is of such magnitude that there is an unknown factor as to how the hemispheric climate system will deal with this. Previous years under similar conditions can provide some historic evidence but there remains a slight unknown element as to how the warmth will influence seasonal weather patterns. Positives By far the most positive signal is that from the arrangement of Sea Surface Temperature Anomalies (SSTAs) across the northern hemisphere from the Japanese coastline to the Bay of Biscay. These continue to develop favourably day by day. Rossby Waves (the large scale atmospheric currents circling the globe) are known to be highly sensitive to SSTAs. These are most potent in influencing these waves and the pressure patterns associated with them when they occur in specific sequences. Indicated below are the key SSTA sequences and the mean surface pressure projected with them: Correlation with the classic signature of a -ve North Atlantic Oscillation (NAO) with warm mid-Atlantic pools sandwiched between cold pools to the north and south is very high and shows an almost perfect fit in the Atlantic and sub-tropical Pacific. Other positive areas are: Area A which is likely to be associated with a troughing of the strong Pacific Jet; Area B which is likely to aid in the bifurcation of the jet stream over the eastern Pacific; Area C which is likely to prop up a southerly-tracking jet over the SE United States; Area D which is a forecast developing warm producing a weak Atlantic trough driving the polar jet south over the Mediterranean; and Area E which is a strong indicator for high lattitude blocking. Also note the likely weak intensity of the Canadian Polar Vortex (one of the main culprits for our recent warm winters). In short, the SSTA pattern could not be any better for cold, blocked conditions characteristic of a -ve NAO pattern this winter. Tropical convection This year has witnessed a record number of Hurricanes, but more importantly, record levels of tropical convection - one of the key ingredients in the formation of tropical storms. High levels of tropical convection have been linked as a strong signal for -ve NAO patterns in subsequent winters. Greenland High The Greenland High has been a feature of our weather ever since February 2005. Throughout the Summer has remained a consistent surface high pressure with below average temperatures for most of this period. This is now evident in the level of snow cover and temperatures being recorded - dipping down to record levels in October with widespread -30 C 850 hPa values. The Greenland High is one of the most fundamental keys to unlocking cold weather in the UK and a feature of high lattitude anticyclonic blocking typical of a strongly -ve NAO. Pattern matches ENSO is a key influence on global weather patterns. Under neutral conditions as we observe now, there have been only two occasions in the last 50 years matching a neutral ENSO and 3 consecutive warm Autumn months. Both 1959 and 1978 were typified by unusual autumnal warmth followed by sharp winter reversals with at least two months with a strongly -ve NAO. These years were characterised by a +ve NAO Autumn. This year has been warmer than these but with a less +ve and often -ve NAO. I put this down to the impact of forced warming, deepening the Atlantic trough and sustaining the strong European ridge keeping us in a more or less constant stream of southerlies. There are indications of a possible weak La Nina phase emerging with cold pooling in the eastern Pacific. If this were to be the case, pattern matches under similar conditions flag up 1970, 1983. 1984, 1995 and 1999. The winters of 1984/5 and 1995/6 were anomalously cold and followed a similar pattern to now although both years were proceeded by a -ve NAO November. 1999 was an anomalously warm winter with a SSTA pattern that on the face of it, is very similar to the present: http://weather.unisys.com/archive/sst/sst_anom-991114.gif However, this year differs in that we do not have a strong La Nina whilst a cold SSTA developed in the eastern Atlantic during the key winter months which effectively maintained a run of SW winds throughout December, January and February. Latest modelling from the NCEP overlaps well with previous runs and predicts the warm pooling in the central Atlantic to become more organised, no major cold pooling along the eastern Atlantic and a slackening of any La Nina development back to neutral ENSO conditions during late Jan-February: http://www.cpc.ncep.noaa.gov/products/anal...s/glbSSTSea.gif The lesson from historical parallels is therefore that under similar conditions, excessive Autumn warmth is met by a sudden reversal in temperatures during the winter months. Crucially, none of the warm winters experienced in the last 10 years outside of 1999/2000 have come close to the SSTA and ENSO conditions now prevalent. Statistical forecasts - UKMO and others - ve NAO The UKMO statistical model has forecast this winter with a NAO of between 0 and -2. This was based on May SSTAs across the N.Atlantic. Other teleconnection models have arrived at a similar conclusion from slightly different methodologies adding weight to the prospect of a -ve NAO winter. This does not on its own constitute a cold outlook however - a deep Atlantic trough would also constitute a -ve NAO for example. Interestingly the -ve NAO forecast made by the UKMO for 1999 was wrong: http://www.met-office.gov.uk/research/seas.../nao/index.html Neutral impacts Polar vortex With a neutral Artic Oscillation forecast allied to the SSTA pattern in the Arctic Circle and N.E. Atlantic, the Canadian Polar Vortex should represent a less strong driver of the polar weather patterns this year, favouring the anticyclonic blocking to the east across Greenland and Siberia. The Alaskan vortex is predicted as being the more influential and active of these features this year. Assumptions ENSO neutral or weak La Nina conditions to persist. SSTA pattern not alter significantly beyond expectation. No other events such as major volcanic eruptions. Verdict For the first time in perhaps 10, maybe 15 years, there are many more positives than negatives with a quite rare coming together of many if not all of the factors to sustain a colder and more 'blocked' winter than average. For these reasons we stand the best chance in over a decade of sustained cold and widespread snowfall. History tells us that under similar conditions, excessive Autumn heat is met in kind with Winter cold which paves the way for a cold outlook. Keep your eyes out for the final November CET - the warmer the more likely for a dramatic turnaround into December. Although analysis of the current position places us just behind the ball line in terms of temperature anomalies over Eurasia, given the likley cooling and low solar activity in the next 3-4 weeks I am sure the situation will begin look very promising - I would however just prefer to see temperatures drop off in the next 2-3 weeks though for confirmation of this. I don't buy into the snow cover predictor as it does not satisfactorily explain the anomalous 1986 and 1990 years whilst taken to its logical conclusion, this theory leads to no winter at all. A convenient theory to explain the last ten years as far as I am concerned. This leaves numerical models which as we know are subject to variation. I find it striking that the UKMO persist in virtually over-ruling their dynamic outputs with their -ve NAO statistical forecast. With many of the positive factors 'already in the bank' and reasonably robust, this Winter cold continues to look stronger and stronger a probability with SSTAs being the major driving force. With cold pooling restricted to the pole at present and the legacy of the last tend years' warmth, we cannot I suggest achieve the cold extremes of 1962/3 or 1978/9 and there will inevitably be mild Atlantic phases of weather. There is likely to be an initial dilution of cold air as it spreads out over Eurasia although with a solar minimum approaching, and recent signs of renewed sea ice coverage, there is probability that given a clear run into January, there will be plenty of -10 ° C to -15 ° C 850 hPa air around Europe - cold enough for us Brits. I acknowledge that an emerging La Nina is a possibility this Winter but I'm going to take a punt that it will either be very weak or more probably ENSO neutral based on SSTA forecasts, and also a large spade full of hunch. The forecast does however build-in allowance for a weak La Nina and -ve PNA into the first part of the Winter. Where it could all go pear-shaped I would urge a fair amount of caution as the lessons from 1999 should be fresh in the mind. Any upwelling of cold water in the Eastern Atlantic off Iberia (difficult to predict) would, with the SSTA pattern, lead to a re-run of the strong ridging that we see now as we did back in '99 - a case of the best winter we never had if so. Excessively strong warm pooling in the central northern Atlantic could result in a deep trough which would result in a strong ridge over Western Europe with almost summer-like temperatures. This however is not sustainable as a pattern under ENSO neutral conditions and the trough would likely collapse with all that cold air pushed over the UK. However, this troughing is one to watch as it could get in the way of the continental cool-down whilst a developing strong La Nina would put pressure on the Atlantic blocking, and probably result in a more (warm) meridional or even zonal jet flow. My current view is that we stand a 70% chance of a cold, blocked winter and 30% chance of the warmer deep Atlantic trough-European ridge scenario. Given the theory of what can go wrong will go wrong, this should be revised to 60 - 40% in favour of cold. Forecast Trends Winter duration Winters in southern England are incredibly short. 8-10 weeks on recent averages. With the forecast pattern, I would see this extending to 10-12 weeks, with the SSTA forecast suggesting the winter to last well into March. Jet patterns There is a strong signal from an number of sources towards a very blocked flow with strongly -ve NAO. Based on the SSTA analysis, I expect to see a strong Pacific Jet with the possibility of a variable PNA pattern across N. America influenced by the Alaskan Polar Vortex and tendency for the Madden Julien Oscillation (MJO) to lead to bifurcation in the central Pacific: This will lead to a number of permutations for flow across the Atlantic but with strong blocking I expect the polar jet to be displaced far south of the UK, with brief phases where it moves northwards across us and high pressure briefly rises off Iberia and the near continent. Winds from the SE are the most likely sources of milder weather this Winter. We do not often hear about the MJO but under ENSO neutral conditions, it may play a hand and influence the severity and timing of extreme cold (as well as the brief milder interludes) in western Europe as this Kelvin Wave crosses the tropics. Mid December, mid to late January and early February look to have MJO potential for colder phases for the UK at this stage. CET Outlook Taking account of the historical precedents under similar ENSO neutral / weak La Nina conditions and the impact of the warming trend, I would pitch the overall winter magnitude at somewhere between those experienced in 1959/60, 1984/5, 1990/91, 1995/96, and synoptically close to 1978/9 but perhaps allowing for a slightly elevated December temperature due to the impact of the warmed decade. This gives a forecast CET as follows: December in the range 4.4 - 5° C January 2.3 - 2.7° C February 2.5 - 3.7° C With all three months below average in terms of precipitation. December patterns Pre-1990, Decembers often experienced a shot of winter from a potent Arctic incursion and I this year there is likely to be a repeat as the meridional jet pattern starts to really take effect and the Greenland High asserts its strength and retrogresses the Azores high. Expect the first widespread snow event across the UK for 15 years to happen mid December. After this I would favour pressure to rise to our south and west once more before the cycle of the northerly is repeated during the lead in to Christmas, this one more like the 'traditional' Arctic incursion with more a convective element to it - some places in the south remaining dry and snow-less from this one. As for Christmas itself, probably a cold and frosty, but 'green' one. January patterns Into the New Year and a zonal phase with a weak Bartlett high to our south and east is possible related to varying jet patterns across America. But things will be happening to our north and east with the Siberian High developing and a plume of really cold air making its way across the Pole into Russia. This heralds the start of the true -ve NAO phase which should coincide with mid to late January and a proper easterly drawing in -10° C hPa air across the UK with the potential for a few day frosts. On previous 'form', this should last about 10 days before a brief milder spell as the Atlantic air edges in on the back of the Azores High. February patterns One more northerly and the pattern of mid to late January is repeated in relation to the MJO. The period between late January and early February is, in my opinion, likely to be the most memorable for at least 15 years. And beyond …. .. Let's just say this Winter will be the beginning of the big one in 2007/8 timed to coincide with the low point of the current solar cycle, SSTAs permitting of course… But for now, get set to rekindle those memories of winters past. Glacier Point

Morning all. The final piece of data now in and this completes the build-up to winter- the SST forecast from NCEP: http://www.cpc.ncep.noaa.gov/products/anal...s/glbSSTSea.gif the main highlights being: 1) Warm pooling central Atlantic set to intensify and remain in close association with cold anomalies off the eastern Seaboard of the USA, with colder anomalies across the sub-tropical Atlantic - perfect symmetry with an anticyclonic blocked Northern Europe. 2) Pacific cold pooling west of Canada set to stabilise and then decline - weak La Nina going back neutral. There is some uncertainty here but I think it's safe to plan for the contingency of both occuring - ie. highly variable jet pattern across the USA switching +/-ve PNA pattern, most particularly associated with Maden Julien Oscillation in sub-tropics. 3) Cold pooling to north not shown by resolution maps but assumed to stay in place with no major incursions up the Davis Straights of warm water. All in all, pretty continuous with the last output although I am slightly sceptical about the forecast degree of warm anomaly in the central Atlantic from where we are now: http://weather.unisys.com/surface/sst_anom.html This is an excellent recipe for a displaced polar jet well to our south with some residual flow up the western flank of Greenland and stronger sub-tropical flow stemming from the central Pacific. I will be in a position soon to post my seasonal outlook. Regards GP

SP, I have looked at comparible years to see where we stand in respect of cold air coverage. For my selected years (1959, 78, 84 and 95 - years with neutral ENSO and weakly developing La Nina following periods of El Nino then ENSO Neutral conditions), comparisons reveal: 1. The extent of the cold air denoted by the polar front is comparible, if not as much as any of these years. 2. The extent of what I would term 'intermediate polar air' at between -20 and -30 C 850hPa is very much less in 2005, noticeably so even with the more recent 1995 comparison. As a result, Eurasia appears to be anomolously warm despite the realtive greate extent of the polar front. 3. The core cold air is located over Greenland as with all years although this year would appear to have colder than normal values associated. It is also worth noting that the -30 C 850 hPa values are as far south as they have ever been in the comparison years. So the conclusions to draw ? i) The polar air mass would appear to be on a par with the comparison years, if not greater so there are no issues about warming synoptics - perhaps indicative of the lower solar activity year taking effect. The only difference is that the extent of intermediate cold air which would be necessary to bring 'average' values to the continental interior is missing - a dilution effect if you like. ii) Really cold polar air exists over Greenland, and the very low values allied to the low lattitude of this cold are also perhaps suggestive of falling incoming radiation and the synoptics of the last couple of months. So we are not behind the game in terms of patterns but definitely so in terms of playing catch-up for the effects of the last year's warmth. The trend is very definitely positive although this does obviously flag up the relative high point from which we start. Regards GP

Our friends over at wxrisk.com certainly know their stuff. Two issues I would guard against though:- 1. Predicating the mean troughing forecast in the eastern Pacific on currently observed SSTA / AO is a little dicey, particularly as the Pacific Jet is likely to become unstable and could go the other way (although agreed at the moment this looks only likely in relation to MJO). 2. Calling La Nina is a little early - we need much more evidence than currently shown and reassuring noises from NOAA and last UKMO 3.4 region place it somewhere between 0 and -1. If it carried on for another month or two, then I think we could be justified in the La Nina pronostication. Also, I'm not sure about the movement of the cold pooling off the western coast of N.America - seems to be translating eastwards a little. So ENSO neutral for me until I see more evidence. Definately worth keeping an eye on though and could yet scupper many a LRF although I think fortunatley for us we have our own set of SSTAs to insulate against any mild tendencies from an invigorated polar jet- still I'd prefer a jet over Florida than Newfoundland! GP

Morning all. A post today focussing on the developing cold pool mid-Atlantic and how it might influence the winter. There are four key areas of Sea Surface Temperature Anamalies (SSTAs) across the northern hemisphere that are driving a major influence on the jet pattern at present. http://weather.unisys.com/surface/sst_anom.html These are the warm anomaly in the western Pacific; the vertical alignment of cold, warm and cold pools in the eastern Pacific, the amorphous warm blob in the central Atlantic and cold pooling to our north. One developing situation is a notable area of cold pooling within the warm central Atlantic, not shown very well by the Unisys analysis, far better by the NOAA: http://www.osdpd.noaa.gov/PSB/EPS/SST/data...t.11.1.2005.gif Surrounded by converging air over the warm anomalies, this area could develop into quite a strong a persistent feature, most likely a strong mean high pressure area. Whilst this may not fit the profile of a perfect -ve NAO pattern (it would have to be much further south of its current position), if this persisted I would suggest that it would form a useful feature in helping to trough the polar jet just to the south of the UK, setting up an interesting west-east battleground scenario. However, caution is urged as if the polar jet leaves the USA on a much higher trajectory we could find a re-run of last year's warm northerlies as tropical air is funnelled over the top of the high pressure block. Once again, the trajectory of the polar jet over the 'States provides for me the key determinant of the winter pattern. Other notes of caution are that this feature may disappear completely, as the last NCEP forecast predicts: http://www.cpc.ncep.noaa.gov/products/anal...s/glbSSTSea.gif The updated forecast due in the next week will be very interesting to see how this is modelled, so one to keep an eye on at present. Regards GP

Indeed, much to be pleased for the longer term prospects. Evening all. Today's 12Z GFS 200 hPa modelling mirrors well the SSTA pattern across the Pacific, Atlantic and Western Europe: http://wxmaps.org/pix/hemi.jet.html which shows the divergence of the east Asian jet over the Pacific in line with the warm anomaly there; the low trajectory flow over Florida and downstream ridge in the central south-western Atlantic; troughing over the northern Atlantic in line with the warm anomalies there; some split flow into northern Africa corresponding with the warm anomalies SW of Iberia and west European ridging into Scandinavia care of the downstream effects of the Atlantic trough and the effects of warm anomalies in the North and Baltic Seas alied to a slightly cooler Mediterranean. In short, there is almost a perfect correlation between SSTAs and jet patterns. This has been the case now for some time, possibly since May. In the short to medium term, I see no reason why the pattern should not change markedly. The Ferrel cell is programmed to progress eastwards and transfer the wave pattern mid Atlantic and assist ridging of the Azores High with a slight rise in pressure over the UK as it does so by the 12Z ECMWF: http://www.ecmwf.int/products/forecasts/d/...2512!!/ This should only be a transient feature before the cell withdraws westwards - drawn in by a flattening of the sub-tropical jetstream over southern California. After this I think further troughing in the mid Atlantic will arise with height anomalies once again over Scandinavia keeping the UK in a very wet and windy but unseasonably mild pattern well into November. Before the SACRA members reach for the bottle, don't despair, it will only be a matter of time before the descending jet over the USA, the decrease in tropical storm activity, the increased stength of the Polar Cell and a falling off of SST anomalies across the Seas of western Europe shifts the whole pattern southwards. I would suggest the best thing to happen at present which would hasten this would be for the warm anomaly off Iberia sinks southwards and ideally a little further west. So far so good. Regards GP

A herculian effort Steve, one I'm sure members experienced and new will find of benefit. Perhaps we should start selling T-shirts with pictures of the Greenland Ice Sheet on them ? Just how much will that influence our winter ? GP

The old conundrum, +ve PNA bad or good for west European winter ? I think the trend will be very much towards a +ve PNA pattern this winter with large +ve SST anomalies off the NW coast of N.America, colder ones further west and cold anomalies to the south-east around the Caribbean. The NOAA seasonal temp and ppn forecasts seem to bear this out. The implications of this for us I flagged up yesterday, but in essence a +ve PNA could still be good news IF the sub-tropical jet takes centre stage. But, I would agree a (strongly) -ve PNA and -ve NAO is thoroughly good news for us, particularly if accompanied by a -ve AO. The situation developing now reminds me of late July with blocking further NE and the Greeland High gaining strength combined with strong ridging over the eastern seeboard of the USA. GP

I would describe Summer 2005 as very much a good one with an experience of plenty of dry, sunny and warm weather. Synoptically, the most striking aspect of the southern UK Summer has been the dominance of the west European ridge which has resulted in the near drought conditions here and severe drought in Portugal and Spain: http://www.ncdc.noaa.gov/img/climate/resea...-drought-pg.gif My summary would be of an early Summer which differed from recent ones with repetitive ridging of the Azores resulting from bifurcations in the jet over the USA and a strong +ve PNA pattern. Then followed a run of brief 'monsoonal' type events with enclosed lows associated with northern blocking during late July which, had they not occured, we would be experiencing one of the most memorable of Summers given the late August weather and return to the Azores ridging. GP

Moderate snow started 12.15 ish 8 miles east of Worcester. Large flakes and settling. Note we are very low lying so snow here is a very good sign for anyone else.