Glacier Point

Thanks Brick, The warm 100 hPa is showing up nicely within a continuing stratospheric warming event going on over the western side of the polar region which could further accelerate the volatility and progression of vortex decay in the next few weeks. Also worth considering are the changes in SSTA over the last month towards an Atlantic Tripole which could sustain / add to the development of -ve NAO conditions during March: http://weather.unisys.com/surface/sst_anom.html GP

For somewhere which has not seen significant snowfall in 16 years, this output is a big deal: http://www.wetterzentrale.de/pics/Rtavn304.html and the drop off in projected surface temps Friday morning is quite impressive: http://www.wetterzentrale.de/pics/Rtavn4817.html On this evidence, any fronts (especially faster moving ones) will have to go over this cold air reminiscent of the 1980s which also dumped 15-20 cms quite rapidly before the change to rain. Saturday still looks very juicy, even for my low level locale for a time - snow falling on lying snow, now that hasn't happend here since the early 80s I think.

06z has increased the ppn amounts for Thursday and Friday night looks cold enough according to the GFS with heavy rain attempting to sweep in from the SW - could be very tasty for a few hours for elevated locations during Saturday morning before the mild stuff wins out.

I can verify that one - very cold right now. My 'sweet spot' for tomorrow - somewhere in the North Cotswolds, between Birdlip, Cirencester and Fairford.

2nd phaser looks like arriving just at the right time with a cold night Saturday over the snow fields with plenty of ppn to the SW: http://www.wetterzentrale.de/pics/Rtavn842.html http://www.wetterzentrale.de/pics/Rtavn844.html http://www.wetterzentrale.de/pics/Rtavn8417.html and I would suggest this is also subject to possible upgrades..

http://www.wetterzentrale.de/pics/Rtavn2881.html I like where this is heading....

Following up yesterday's outlook, some analysis of where the ECM blundered this week but continuing trend for something quite tasty in 10 days time... If we compare Friday's evolution since it was first programmed, we can see that the ECM (like many models JMA excepted) failed to come to grips with the height rises over Iceland and the draw-down of cold air across its eastern flank. This series (in chronological order) depicts attempts to break the heigt rise down or shift it further east: Just at present there is a hint in the broader modelling that this is continuing to happen with undercutting lows rather than the main depression and upper level trough making its way eastwards towards the UK. There is some risk that the models are continuing to make the mistake of the last week in underestimating these height rises to our north although I think on balance the call would be for a brief warm up post this weekend. The 00z ECM however picks up my thoughts last night nicely: What we see here is a distinct split flow developing across the NE Pacific [ALERT - models will struggle] with a lot of energy going southwards. This sets up a rather slack looking flow to our north with a gradual migration of +ve height anomalies from Scandinavia across Iceland to southern Greenland - bang in line with the expected fading QBO pattern. From a forecasting perspective we cannot place any faith in this emerging trend just yet given the uncertainty in the shorter term but this I believe is the evolution to be looking for, and which could potentially arrive sooner if the blocking to our north is continued to be underplayed. GP

A few thoughts on what has been and what may come to pass..... Back on the 25th Jan the analysis was of a dramatic transition period with high latitude blocking becoming more of a feature with a split polar vortex and potential snow event. The blocking may not be as prolonged as anticipated but the AO looks pretty supportive of a big hemispheric change. As for the snow event, we'll just have to wait on that one a little. Looking at the AO, the trend is clear to see: ..... a downward correction fuelled by strong ridging into the pole across Alaska as the ridge there steadily built and greater flow went into the southern jet over the Pacific then transfered eastwards towards the Atlantic in association with a deep trough over the eastern and mid west USA. The combination of greater energy going into the southern jet and confluence of the jet over the western Atlantic was always going to cause the models huge problems and so this has come to pass. This was all timed with the weakening of the QBO - as monitored throughout the second half of January - the average monthly value was 2.71. High altitude westerly winds are still flowing over the equator indicating that we are still in the westerly QBO regime although surely its days are numbered and I think we are looking for a change-over to an easterly QBO during late Feb or early March. This is interesting in itself as we have seen precious few late winter changeovers and this will almost certainly co-incide with the final breakdown of the polar vortex, potentially leading to some quite potent weather events as it does so. Looking at the thermal anomalies over the polar region, we have seen many changes in the last 10 days indicative of both the shifting QBO and its impacts on height anomalies over the Pole (the AO). Late Jan Early Feb Here we can see a building of warm air anomalies at around 100 hPa over Greenland and cold columns towards western Siberia, and, indications of some Stratospheric warming starting to occur at the very margins of the Stratosphere which may propogate downwards and across the Pole to Canada in 2-3 weeks time. The sharp shift in heights over the Pole is shown nicely here by the CPC.... The reanalysis of the polar thermal profile for weak westerly QBO Febs is supportive of this type of evolution - note the pattern of anomalies - warm at 100 hPa and cold at lower levels towards Scandinavia. This is an ok sample size for this set-up and could be taken as a reasonable guide to the likely evolution in the next few weeks towards the end of Feb. At 500 hPa, the height anomalies suggest southern Greenland to have a strong +ve anomaly (blocking) and deep -ve anomalies towards eastern Europe. Up until the 12z ECM for 05/02/07, the models have not shown any hint of big -ve AO manifested as blocking over Greenland. Then up pops the ECM showing at the t168-240 range some substantial blocking which fits nicely the predicted QBO reanalysis pattern as well as declining El Nino for Feb. This is not occuring out of the blue - the model has been working on average heights for the time of year over the last few runs and although it could be a one off, the trend is good. Other long range modelling (and some ECM) has been for height rises towards Scandinavia for the blocking but I think this is where we may take our eyes of the real deal looming on the horizon. With the ridging stubbornly persisting over Alaska we continue to fuel height rises over the Pole and divert flow into the southern Pacific Jet. With height rises over Greenland associated with the weaking QBO (and I would contend the underlying pattern which has until now been masked by the westerly QBO / solar minima / stratospheric cooling trinity), we could conceivably complete the equation which we have only now fleetingly achieved. Remember, just a transitory -ve AO / -ve NAO / +ve PNA phase has managed to deliver cold to the UK. Now, the task is to lock these three into place and as I see it, there is at the very least some opportunity to fully achieve this. But isn't it too late ? Maybe, but with the solar minima and collapse of the polar vortex timed for late Feb, there is I think every prospect for Winter to overrun quite considerably this year until mid-March. GP

.... [cough] http://www.netweather.tv/forum/index.php?s...st&p=905957 GP

Fax charts will be the best guidance on offer at the moment and IMO these are considerably better for snow prospects than the 06z GFS. The first potential is from the shallow low moving in Wednesday: http://85.214.49.20/pics/brack1a.gif Thursday sees a seconday feature bumping up against some likely cold air at the surface Midlands northwards (thicknesses don't look quite so good so elevations likely to be important). http://85.214.49.20/pics/brack2a.gif Thereafter we see sub 528 air swept back southwards before the main system attempts to approach from the SW: http://85.214.49.20/pics/brack3a.gif with potential for an hour or two leading edge snowfall even down to lower levesl and the milder air wins out eventually but probably not without a fight. Even at this range the GFS is errant. GP

I think this Scandinavian block is something of a red herring, at least in the longer term..... Worth also noting that the QBO value for Jan was 2.71 - extremely weak suggestive of a highly volatile polar airmass and some evidence of Stratospheric warming taking place over the western hemisphere. Perhaps we should be focussing on southern Greenland for our next block ? GP

A possible record mild winter and possible breakdown of the polar vortex should make the range of spread huge. The context is: 1) mild trend established - add 2 to pretty much all forecasts; 2) polar vortex starting to look unstable and fragmented; 3) weak and declining El Nino; 4) westerly QBO surely on borrowed time by now, all of which doesn't help us much but to suggest perhaps something a little less record breaking is the order. Both El Nino and QBO reanalysis suggests height rises towards Greenland and add in the lowering of heights in the Atlantic, a progressive rise of heights to the north will be a feature as we progress through February. But will this be of use to us ? The first half of the month looks like being a W-SW flow and potentially the remainder from less warm vectors. All in all, within range of average which I think will be a shock to the system after this excessive warmth - my punt 5.2C

A lot is going on now suggesting we are on the verge of a second, more progressive pattern change favouring cold. The QBO has declined to weak values, especialy over the last ten days or so. This reanalysis shows the change on anomalies of 30mb zonal winds with an already weak QBO in decline: Weak westerly QBOs have a major bearing on the state of the polar pressure anomaly or the AO with the breakdown of the polar vortex related to the state of the QBO - a weaker QBO gives a better chance of the emergence of +ve height anomalies over the North Pole. Reanalysis of the 7 Februarys with a weak westerly QBO suggests the following 500 upper pressure anomaly pattern: Points to note - the ridge in the NE Pacific, strong trough into Canada, deep -ve anomalies into Scandinavia and ofcourse a strongly -ve NAO signal in the Atlantic. Interestingly this suggests that the weakening QBO tends to favour a splitting of the polar vortex into Scandinavia and North America. The solar flux is an important consideration for the state of the QBO and for the two years in our reanalysis when there was a solar minima (1962 and 1964 (1964 was also a weak El-Nino), the reanalysis looks like this: Similar but with the NAO less -ve and the Atlantic block closer to the UK although this is a low sample. Looking at the polar thermal anomalies, we have seen a dramatic change during mid January. Compare the 13th January profile with the 21st January: Showing an extension downward and narrowing of the columns of cold air with two distinct columns towards Canada and Scandinavia. Coincidence or as a direct result of the weakening QBO ? I suggest the latter. With the ECM and GFS Ensembles continuing to support the development of the Alaskan ridge forcing height rises over the Pole and deepening trough into the eastern USA and Canada, we have potentially the embryo of a sustained -ve NAO phase. The next evolution to look for is height rises over southern Greenland as the jetsream is forced southwards as the trough across the USA deepens sufficiently to bring the sub-tropical jet into play. The worst case scenario I see is a blocking high to the WNW of the UK as the AO is not strong enough to recover from the earlier stratospheric cooling. The best case scenario for cold is for a sustained -ve NAO with a strong Greenland block in place presenting numerous opportunities for depressions to try and undercut from the SW - the huge snow potential I mentioned a few days ago. Now before we get too carried away, this is just around the t240 margin so plenty to be cautious about and I would again urge some consideration that this type of synoptic need not deliver brutal cold to the UK as we can be located just out of its reach whilst the near continent freezes. For the record, the weak QBO composite predicts deep cold to penetrate Scandinavia and sub-normal temperatures for the southern UK: GP

As part of my winter forecast, I made use of a constructed analogue based on three years providing solid matches for El Nino, QBO and SSTA. Two of these years, 1963/4 and 1977/8 have verified extremely well in terms of November's pressure anomalies: Observed Constructed analogue and they look uncannily like the current situation in relation to the polar vortex with 1963 in particular providing an interesting parallel. This is the comparison of the polar thermal profile from mid November onwards: 1963 present The profile for 1977 was also similar and the analogues suggest a trend for the polar vortex to shift from Greenland to Scandinavia and then east to be replaced by a dramatic change to positive temperature anomalies at mid and upper levels by the end of December. During 1963 this evolution was quite rapid with the cold stratospheric anomalies transferring downwards to form a new vortex over Siberia within the space of 7 days. From this:- To this:- What relevance does this have to the current situation? Well, here we have two years which have a strong similarity to the weather we are currently experiencing right now, two years with a very similar profile in terms of the polar airmass and major teleconnections. They suggest a big pattern change is likely during December. The Arctic Oscillation is projected to go through the roof over the next 5 - 10 days: http://www.cpc.ncep.noaa.gov/products/prec...ex/ao.sprd2.gif This could well be the sign of a massive period of volatility hinted at by the analogues. The timescales do not however fit the historical matches and this is where I think we need to factor elevated hemispheric temperatures and a lag effect. For interest the period 5th to the 14th December of 1963/77 looked like this which should translate to the trend for the second half of December 2006: ...showing big height anomalies to our north and low pressure to the SW. Then up pops the 12Z GFS..... perhaps not the perfect match for the composite analogue - but indicative of a dramatic shift nonetheless. None of this means anything though until it starts to show up in ECM plots as well as the 'edge of the rainbow' GFS. Keep watching. History at least suggests the second half of the month has at least some potential for a pattern shift. Whether or not we will have to wait and see. Also of interest will be how quickly any (if) any change takes place and at what stage the modelling picks it up - remember the 1963 event took place over a very short period of time. GP

That's actually a pretty good revision to the concecensus forecast on NW with increasing probability of colder snaps January onwards. UKMET were on their own with their strong El Nino and have revised this down to moderate. They may still be over-doing this and we could be in 'weak' territory making the next revision of the forecast downward further a distinct possibility. Also, what gets me, they seem to have completely abandoned or not mentioned the statistical guidance (its mentioned in the preamble) but I fail to see where +ve NAO comes into the forecast ? Once again, I think they have gone with their global forecast model and not the May SSTA method (they did claim last year was a statistical method forecast but I have my doubts about this).

Some negatives and positives this morning. Both ECM and GFS show a broadly zonal pattern associated with a +ve AO and NAO pattern with vigorous hemishpeheric jetstream across the Atlantic, with some deepening of the mid-Atlantic trough resulting in height rises over continental Europe out to 10 days. In the Pacific the strong jet is approaching split flow as it hits the body of cold water off the western USA and there is a notable increase in the sub-tropical jet flow across the southern US over the t144 period associated with El Nino: http://wxmaps.org/pix/hemi.jet.html The polar vortex continues to show positive signs of shifting its core to NW Europe and Russia although the height rises over Greenland indicated by yestedays GFS are not evident today. Notably the ECM solution out to 10 days reduces the intensity of the Eurasian ridge although the jet flow remains strong. The 00Z GFS was dominated by a split jet flow from t228 onwards with displaced high pressure located over NW France and southern UK. This split flow may be a good sign for later cold and could allow retrogression of highs NW to form transient Atlantic blocks. With many opportuinities for model instability now starting to appear in the Pacific associated with a split flow scenario and increasing strength of the sub-tropical jet, the more consistent ECM modelling is slightly favoured with low confidence on outputs beyond t144. GP

Please keep this thread for technical model discussion. Post your general model comments in the relevant thread. Thank you. One of the key signals we are looking for during early winter is a movement of the polar vortex eastwards away from Greenland towards northern Scandinavia and Russia. November and the first few days of December have been characterised by strong thermal anomalies at all levels in this area (60 E- 120E) supporting +ve height anomalies and blocking. This has effectively held in place the polar vortex over Greenland maintaining a strong thermal gradient aloft and flat jetstream across the Atlantic with notable -ve heigh anomalies centred Iceland: This large warm air anomaly may be attributed to seasonal conditions enhanced by the lag effect of elevated hemispheric temperatures and the impact of a stratospheric cooling event during October and November. All of this is consistent with the westerly QBO phase which remains at values around 10. http://www.cdc.noaa.gov/Correlation/qbo.data If we maintain this pattern, there will be no cold incursions during December and temperatures will remain slightly above average. However, there is evidence of some weakening in the height anomalies across this crucial area to our far NE associated with cooling air. Take the last 10 days in November... Polar thermal profile (T. anomalies 65-90N): Polar height anomalies This is consistent with analogues for December under matching QBO and El Nino conditions suggesting a transference of the vortex and dropping off of heights in the key area, possibly delayed by 10 days as a result of elevated hemispheric temperatures: We are already beginning to see this in GFS runs, the first possible attempted breakdown now: Note the development of colder air aloft into Scandinavia and deeper cold at the pole. This is a positive sign of change. This change is likely to take some time to effect, possibly over several weeks with several attempts before the final displacement of the vortex. At this stage we are looking at t288 (15/16th December) as being the possible significant transition so this is beyond publically available ECM outputs and the variability of GFS runs gives some cause for concern although it has been showing in a number of recent runs. The sudden death of the MJO has complicated the timing of any possible pattern shifts although any revival of the wave (if) when it enters the Pacific could enhance the transition to a colder winter pattern. This could of course be complete rubbish and the warm air / +ve height anomalies re-establish to the NE. We are talking a long way out here, but any continued suggestion of transference of the vortex towards Scandinavia would be very encouraging for cold lovers. To emphasise the uncertainty going on here, compare 04/12/06 500 hPa height anomalies for GFS and ECM 8-10 day: No joy there on the ECM just yet - strong blocking Eurasian ridge. GP

I think this should be a consensus thing, but my view would be no. There have been plenty of opportunities since this thread opened on the 21st November. However, it would be to the competition's loss to exclude people and we discussed a rule where you must compete in 10 out of the 12 months. So, if you missed December, you'll have to sit it out and come back on January without forfeit other than loosing ground on Ian Brown or Summer Blizzard. SF: I think the compilers got brain ache just logging the entries, let alone having to work out points for xdays prior submission. If that rule applies, my entries for the next 11 months will be average submitted now thanks.

Last call for CET predictions, leg 1 CET Trophy midnight tonight. Thankyou.

I may have under-cooked the +ve temp. anomalies for the first half of the month somewhat, certainly looks that way from GFS and ECM extended range outputs which are likely to come in +1.1 C. I'll upgrade my CET projection to 4.8 C

December, 1st leg of the CET Trophy and 1st part of the winter forecast period. The key players this month are likely to be:- state of the polar air mass; a moderate strength El nino; intensifying MJO activity. A persistent polar vortex parked to our north has raised some real fears for the coming winter. At an upper level, the thermal profile is very much in line with the influence of the westerly QBO with quite good match for cold air at upper layers forcing -ve height anomalies and a strong polar vortex with the AO forced +ve. http://www.cpc.ncep.noaa.gov/products/prec...hgt.ao.cdas.gif Were this Summer, I would have no hesitation in calling it mild all the way although these types of cold air anomalies are not unusual for winters and may indeed be integral to laying the foundations for a cold season. The key requirement is for the cold air to rapidly propagate downwards and set up over Scaidnivia and western Russia, as it did in 1963: November 1963 December 1963 Statistically December is a favoured month for the AO and NAO to be +ve, even under westerly QBO conditions. The weak to moderate El Nino remains in place although its impacts have been a little masked by the polar anomalies of late. I expect to see a return to a more traditional El Nino pattern for December. The MJO has entered it's second Wave of the season and is currently slightly bogged down in Phase 3: http://www.bom.gov.au/bmrc/clfor/cfstaff/m....Last40days.gif With SSTAs in the Indian and Pacific Oceans remaining favourable, it is likely that the wave will re-intensify through phases 5 to 8 and re-enter phase 1 at the end of December. Phases 7,8 and 1 would be considered favourable for high latitude blocking with phases 8 and 1 being highly conducive to a Greenland / Icelandic block to develop which at this time of year would be very cold for the UK. http://raleighwx.easternuswx.com/MJO/DecemberPhase8500mb.gif http://raleighwx.easternuswx.com/MJO/DecemberPhase1500mb.gif I expect this to be a major player towards the second half of the month with the 1st half being more of the current projected pattern resulting in average or just above conditions for the UK. The Winter Forecast Constructed Analogue suggests an average or slightly below average month with +ve pressure anomalies to the north and north-west: With the first half of the month likely to come in marginally above average, the key to December will be the magnitude of the correction thereafter. Warming of the Davis Straits during October, the underlying -ve NAO and phasing of the MJO are likely to lead to downward correction for at least 10 days and my play is for December to be below average with a CET of 4.5 C - but this could easily be lower.

Just a reminder that this is proposed as round 1 of the CET Trophy. Subject to general approval, I think we should endorse the 'operational' scoring system as devised by Stratos Ferric. The basic gist - get as close to the Hadley CET as often as you can. Paul has generously agreed to supply the following prizes: 1 Winner receives Year's subsription to NetWeather Extra and champions' Crown. 3 Runners up each receive three monthly subscriptions. Each seasonal winter (aka Winter King / Queen, Spring Supremo, Summer Star, Autumn Ace) will receive 1 month's free subscription. Rules as advertised before. However please note, I think we agreed that the deadline for submission into this thread was 23.59 30th November 2006. No late submissions accepted - deadline 23.59 GMT November 2006. Because we are proposing to use a scoring system which in part rewards consistency, people may attempt to tatically abstain from tricky months which is not really in the spirit of the competition. It is realised however that holidays etc. might interfere with some entries so you will be allowed 2 months non-entry throughout the year. Each non-entry will however result in a deduction of 10 points. More than 2 missed months over the year will result in disqualification so it's up to you to make sure you get your entries posted on time. Good luck. GP

Are the Daily Mail going to serialise it ?

The persistence of warm SSTAs in the central and western Pacific has been a feature of the last few months. This is very much a pressure anomaly pattern associated with a -ve Pacific Decadal Oscillation (PDO): (remember this is a correlation reanalysis, so a -ve PDO is the reverse of the SSTA and pressure anomalies shown) which is very consistent with ECM height anomaly modelling at present: http://www.meteo.psu.edu/~gadomski/ECMWF_0z/hgtcomp.html The lag effects of the SSTA are also probably influenced by increased amounts of blocking across Siberia and the Kamchatka Peninsula, often associated with this time of year. Whilst this pattern may be quite difficult to shift and is key to downstream influences over western Europe, it will probably 'flip' quite dramatically as the maturing El Nino signal described by Brickfielder and colder air spilling off Asia serves to drag the jet soutwards and decrease pressure over the Gulf of Alaska. GP

October has verified extremely well in terms of expected circulatory patterns based on El Nino's with a MEI of between 0.5 and 1.5. 500 hPa Geopot. height anomalies Predicted: Observed: generally quite representative, particularly for western Europe and the east Atlantic.The blocking over NE Canada is obvioulsy stronger although not directly related to ENSO. 200 hPa zonal wind anomalies Predicted: Observed: Once again, not bad and picks out the increased strength of the sub-tropical jet across the Atlantic already - a lot earlier than the composite years suggest. MSLP anomalies Predicted: Observed: very good agreement on the pattern for western Europe, N. America less so related to notable cold incursion. but the real pattern match, 850 hPa Vector wind anomalies Predicted: Observed: Confirmation that a weak becoming moderate El Nino has begun to impact on the hemispheric pressure patterns and will continue to do so, playing a leading role in determining the winter to come. I'm struck also by the strength of the anomalies suggestive that the gradients between cold and warm, high and low pressure are very much more intense this year compared to the composites. This is evidence possibly for a more extreme type reaction within the climatic system to ENSO and possibly the polar air masses this year. GP