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    Gwo And Global Angular Momentum


    BrickFielder
    Paul

    Please be aware that these comments were copied here from another source and that the date and time shown for each comment may not be accurate.

    Message added by Paul

    Glacier Point said:
    Where do you see the GWO going in the next few days Mark ? If it's back to phase 1-2, some support for Icelandic block, phases 3-4 and more of the Atlantic influence perhaps ?

    Ok I will start a new thread for dicussions along this line and perhaps I will draw on some ideas expressed in the stratospheric thread and artic sea ice thread. I guess you would be the best person to explain all this GP but for those who don't know this thread is about global angular momentum and how it oscialltes up and down (Global Wind Oscillation) along the lines discussed by Ed Berry.

    Angular momentum is of course a measure of the turning force in the winds, so could perhaps be considered a measure of the strength of low pressure systems, but also relates to how much the jetstream undulates and how much blocking we have.

    The budget of angular momentum goes up and down as energy is lost as weather systems crash into mountains and increases as cold air meets warm. Each phase of increasing and decreasing momentum suggests different types of weather for the UK. Looking at the current GWO plot we see a liklihood of going into phases 3 and 4 based on how it usually cycles round.

    This implies increasing angular momentum as the various torques including mountain torque diminish (i.e those things which take energy out are not active).

    This is certainly true of mountain torque.

    For frictional torque and gravity wave torque then the jury is out.

    Overall it looks like global angular momentum is on the increase.

    The tendecy during december has been upwards.

    Short term I think we are looking at phases 3-4 and more of an Atlantic influence. What I am guessing at though is that low pressure systems crossing the US will increase mountain torque, equally the jet stream across india is not a weak flabby one which might increase asian mountain torque. The strong jet in the western pacific along with OLR charts suggest strong trade winds with a stationary high to the north east of Australia and convectional activity to the north west of Australia. So back to phase 1-2 fairly quickly I think afterwards.

    All maps are available in the link below.

    PSD Map room for AAM

    I am sure GP will tell us what he expects from the MJO and convectional activity in the pacific and how and if he expects rossby wave development as a result. It is those Rossby waves which in part will affect the stratospheric vortex and the low angular momentum could be linked to a more blocked pattern and sea ice build up to our north which I talked about in associated threads.

    What we should always remember though that this a complex interaction of parts of which the stratosphere plays a large part during the winter.

    Please note that this post and subsequent comments have been copied from the forum, so the dates/times of the comments are not correct.

    Edited by Paul

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    Ditto me too! Thanks GP- great post and rubber stamps the increasing train of thought over the last week or so.

    On that basis, easy to forgive an imminent snow event maybe being too brief for some of us!

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    From what I have gathered the increased easterly winds in the northern hemisphere at 200mb in the polar latitudes have caused the sudden stratospheric warming, or as you like to call it the Major-Mid Winter Warming; to my knowledge it hasn't been this strong during this time of year since 1978.

    This would set up high latitude blocking over the Northern Atlantic and hopefully some more winter cold outbreaks.

    By the way, awesome discussion.

    I still learning how to put the pieces of the puzzle together like the momentum fluxes and frictional torques. I hope that these discussions continue.

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    I'm posting this here in response to the discussion regarding this paper http://ams.allenpress.com/archive/1520-046...69-22-6-597.pdf .....in the Model Output Thread.

    I personally think that Winter SW warming events are "linked" with cold winters and that recent "bad" winters were ruined by the strong omnipresent PV.

    However this paper begins by talking about a mid-Jan 63 warming as contibuting to that phenomenal winter that I remember so well.

    However the Autumn of 62 had been mostly very cold and the extreme cold synoptics were in place by Xmas day. By mid-Jan we were 3 weeks into an uninterrupted regime of extreme cold.

    If the Warming takes 2 weeks to alter the synoptics, then we had already had 5 uniterupted weeks of record-breaking cold, by the time the "cause" arrived!

    Perhaps that winter was caused by other factors.

    Or perhaps the SSW is not the direct cause? Could it be a parrallel effect caused by a deeper, unknown, cause that promotes cold NH winters?

    Could it be a "marker" rather than a simple cause? Or a self reinforcing "product-&-further-cause" of cold.

    Notwithstanding my queries about it "causing" the 62/63 winter I still think it's the best explanation we have for "good" and "bad" winters.

    Please keep up the info. GP et al.

    Len

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    I'm posting this here in response to the discussion regarding this paper http://ams.allenpress.com/archive/1520-046...69-22-6-597.pdf .....in the Model Output Thread.

    However this paper begins by talking about a mid-Jan 63 warming as contibuting to that phenomenal winter that I remember so well.

    Len

    re the above link Len.

    I'm not convinced by that article, although I am fairly well convinced by the general argument that events in the Troposphere are linked to what has happened in the Troposphere. Their argument, if it is to try and explain the severe winter of 1962-63, falls down as by mid January the severe cold had been in existence over much of the UK since just after Xmas.

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    So here we go, the real deal is about to begin.

    In terms of the 'actual' weather, I'm thinking sustained and quite severe cold (cold intensifying as we progress through Feb) with a polar trough centred just to the east of the UK feeding in cold north or north-easterly winds with snow and very low night time temperatures throughout the outlook period.

    Reanalysis of the first week of February identifies the following H5 anomaly:

    Note the marked -ve anomaly over Europe and +ve anomaly over Iceland and southern Greenland. I've depicted this to demonstrate the link between the 500 hPa Geopotential height anomaly and real weather, and to emphasise the link between forecast patterns and verification. This chart delivered the snowfall that many of us have seen and a CET which currently stands at 0.5C.

    As anticipated, the GWO has exhibited a high amplitude quasi stationary oscillation in phase 2/3. This correlates well with composites for these two stages, allowing for a weaker zonal wind anomaly across the polar field allowing for the ridge to pull northwards.

    The major stratospheric warming is continuing to propagate down through the tropopause. Note however that this propagation is somewhat discontinuous with sudden increases in zonal winds occuring within the tropopause ahead of downwelling waves. This laddering down of the effects of the warming event is not unusual. It is this switching ahead of the downwelling that is IMO behind the model fragility within the extended range. I had hoped that the ECM as the best upper atmosphere modeller would be able to cope but unfortunately, it would appear vulnerable. Beware, another episode of laddering is likely so perhaps the models to switch like a shoal of fish in a stream and pumping more energy into the polar jet before twigging just what is coming down from the 'headwaters'. I fully expect the huge negative momentum anomaly to have an impact on the Northern Hemisphere's weather patterns for a period over February and at least the first half of March. However, this will intensify and ease off reflecting the nature of downwelling waves.

    The effects of the stratospheric warming show nicely in terms of a negative momentum anomaly within the upper sigma levels and positive anomaly in the lower layers - the prelude to downwelling.

    Mountain torques (pressure differential across mountain ranges) have worked to add westerly wind anomalies to the circulatory system (once again, wavebreaking a possible trigger for further stratospheric warming). Note the cycle of positive torques is more or less tied into the cycle of torques over the tropics (purple line) and the addition of westerly winds is now looking like reversing in a natural rubbing out out of these westerlies coinciding with the tropical signal. A fall is likely adding easterly wind anomalies to the circulatory system.

    These positive mountain torques have added westerly motion to the mid and high latitudes. However, frictional torques (pressure differential between latitudinal air masses) have helped to keep lid on these westerly additions by counteracting and adding easterly winds.

    Tendency in earth angular momentum is now down:

    ..and the overall signal here is for tendency in anglar momentum to decrease, especially as decreasing mountain torques take effect. This will drive the GWO through phases 3-2-1 and back again 1-2-3 as easterly wind additions are rubbed out.

    The composites for GWO phases 1-2-3 once again capture the overall likely longwave pattern - mid Pacific and Atlantic ridges (some suggestion for retrogression) and Scandinavian trough, possibly bridging over as the trough becomes cut off.

    However, as we have seen already, we need to tweak these anomalies to allow for pressue to rise to our north and north-west in the face of increasing signals for blocking related to downwelling waves (remember the laddering though).

    Overall, the thoughts discussed at the end of January remain unchanged - below average to continue with more progressive blocking to the second half of the month - winds from a north-east and northerly vectors. Both GEM t240 00z ensemble mean height anomaly, CPC and ECM mean height anomaly depict this well.

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    thanks Stewart for another fascinating read, most of which I THINK I understood.

    Interesting that several of us, from not the quite same direction, tend to feel that the models are not really showing what is 'around the corner' so to speak.

    I agree that cold or at least below normal is the most likely temperature level for the Uk as a whole, and into March as you say. How far in I have no idea just yet.

    thanks again Stewart.

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    Events in the stratosphere are pretty unusual and the tropospheric response should be linked to the specifics of the type of event going on. To my way of thinking there are three distinct types of event that can occur in the stratosphere.

    1) A split Vortex with both displaced southwards much like we have now.

    2) A single vortex displaced southwards, much like we will have in a few days.

    3) A complete disruption of the vortex which I think may be on the cards after that.

    Lets look at now.

    Temps and the vortex

    Signals for high pressure as a result

    Lets move on 5 days and we see one part of the vortex collapsing as they both rotate around. Unfortunately that collapsing bit moves nearer to the UK and seems likely to give us some more atlantic type weather untill early next week.

    Further out and that second part of the vortex collapses leaving just one part displaced southwards. Vorticty charts suggest here we could be in for another cold period with a risk of snow.

    Even further out and we have to start looking upward in the stratosphere for clues and you need to go almost all the way up to the 5hPa layer before you start to see any kind of vortex reforming.

    Giving very little vorticity in the stratosphere for a period. Meaning other signals will take priority over the stratosphere.

    Those signals will most likely involve the GWO which you would expect to head into phase 1 and 2 but seems to be stubornly stuck in 3 4 and 5.

    I am not really convinced about mountain torque reducing angular momentum which if I understand things correctly means as a cyclone crosses one of the great mountain ranges it transfers momentum to the earth ,taking it away from the atmosphere. My take on this would be although the mourtain torque is falling it is still positive and as such we still have some time before angular momentum falls away. Perhaps this is something for Glacier Point to elaborate on.

    Cyclically it looks like warm water ought to be on the decline in the Pacific, but we do have a stalled MJO in phase 6 so maybe this will come into play. SST's I think will have their day this year if things really calm down so we ought to be thinking about high pressure maybe to the north of the warm spots in the atlantic.

    The upshot of this is that models are likely to struggle a bit with the transitioning phases in the stratosphere and globally we might expect some high impact weather this year as a result of this event.

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    Promising posts thanks GP and BF. I will keep an eye on the potential vorticity charts in the next few days to see how they change. So for those who can look further than the short term variable model outputs still a lot to look forward to with some potential wintry weather possible into March. I didn't think this SSW would give up that easily without something more to show so fingers crossed!

    c

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    Promising posts thanks GP and BF. I will keep an eye on the potential vorticity charts in the next few days to see how they change. So for those who can look further than the short term variable model outputs still a lot to look forward to with some potential wintry weather possible into March. I didn't think this SSW would give up that easily without something more to show so fingers crossed!

    c

    Yes indeed. That was a very interesting post from Brickfielder and adds yet another perspective onto things in terms of how events may transpire. I certainly agree with the notion that the effects of the SSW may well be long lasting beyond the remit of cold and wintry weather. So the post mortem on the event so eagerly awaited in certain quarters on the model thread may well be a very long time coming!

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    Clearly some issues with the transference of negative wind anomalies across the upper part of the troposphere which make previous thoughts somewhat waide of the mark in relation to cold. However, the general circulation has progressed as anticipated. The extended range discussion is likely to continue to revolve around a strong reload of La Nina type pattern and when or if the impacts of a significant stratospheric warming will take effect.

    Latest thermal and zonal wind anomalies clearly show the effects of the warming event to have penetrated between 150 hPa and 200 hPa layer - i.e. across the tropopause.

    Further downwelling is taking place, although at a painfully slow rate. Crucially

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    Doh ! let's try again.

    Clearly some issues with the transference of negative wind anomalies across the upper part of the troposphere which make previous thoughts somewhat waide of the mark in relation to cold. However, the general circulation has progressed as anticipated. The extended range discussion is likely to continue to revolve around a strong reload of La Nina type pattern and when or if the impacts of a significant stratospheric warming will take effect.

    Latest thermal and zonal wind anomalies clearly show the effects of the warming event to have penetrated between 150 hPa and 200 hPa layer - i.e. across the tropopause.

    Further downwelling is taking place, although at a painfully slow rate. Crucially, the zonal winds across the polar region remain relatively light which should allow for the atmopshere to respond to tropical forcing although it is noted that polar vortex is attempting to reform towards eastern Siberia and the NW Pacific sectors which might be resisting so far the pressure from above. The impact of downwelling will I think still impact the surface although when remains a big question mark. The chances of a very blocked March and April have very much increased from my perspective (cold and wet spring?) through the timing and magnitude of the stratospheric event.

    A strong trade wind surge is ongoing in the tropics with anomalous 'Branstrator' mid latitude ridges now evident. Latest tropwave plots depict this surge in the central-western Pacific and also strong anticyclone developing over Equatorial Africa and the western Indian Ocean leading to convective surpression. OLR plots also show this nicely.

    This is signalling a general lowering in GLAAM. Also signalling this, a strong negative mountain torque has developed over Asia which, in tandem with falling frictional torque, is leading to a sharp decline in momentum over the mid latitudes and generally within the atmospheric framework.

    This falling tendency in momentum has driven the GWO through phase 3-2-1 (as anticipated) and resulted in a strong mean ridge in the Atlantic featuring within the likely weather for the medium term modelling. Further falls in momentum are likely and we are potentially looking at a high amplitude orbit through phases 1-2-3 within the next few weeks.

    http://www.cdc.noaa.gov/map/images/gcm/gwo_40d.gif

    Composites for thhese phases identify a mean ridge in the Atlantic and trough over Scandinavia as continuing responses.

    Whether or not the effects of the stratospheric warming detonate into the lower atmosphere during the outlook period is unclear. If they do, this will serve to 'excite' the pattern of ridges and troughs resulting in height rises over Greenland.

    For my money, we are likely to continue with the pattern of ridges and troughs that we see now, possibly with a hint that the last week of the month will start to to take effect;the impacts of the stratospheric warming with decreased momentum leading to a northward shift in the ridge with split flow. I have more confidence in more progressive blocking taking place during March. Organisers of the Cheltenham Festival (mid March), take note.

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    Thanks for the update :)

    I did wonder if you were going to make a mention of the Cheltenham festival in view of the way things are heading :)

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    an idea of the time lag Stewart for it to show, say at 500mb?

    For a normal event John, 21-30 days should have been normal timlag. However, this is clearly not a normal event and it may well be that it will have a slower and much more sustained (inter-seasonal) impact on the circulation of the Northern Hemisphere throughout March and April.

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    Could someone tell me what "nbsp" stands for?

    And also "MMW", which is being used elsewhere relating to Strat. issues?

    Looks like a double whammy from this warming. Not helping Winter; Ruining Spring!

    Len

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    Could someone tell me what "nbsp" stands for?

    And also "MMW", which is being used elsewhere relating to Strat. issues?

    Looks like a double whammy from this warming. Not helping Winter; Ruining Spring!

    Len

    It's (nbsp) a typo Len - I was timed out on the edit and the recovery function inserted it.

    Major Mid Winter Warming = MMW

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    Doh ! let's try again.

    Clearly some issues with the transference of negative wind anomalies across the upper part of the troposphere which make previous thoughts somewhat waide of the mark in relation to cold. However, the general circulation has progressed as anticipated. The extended range discussion is likely to continue to revolve around a strong reload of La Nina type pattern and when or if the impacts of a significant stratospheric warming will take effect.

    Whether or not the effects of the stratospheric warming detonate into the lower atmosphere during the outlook period is unclear. If they do, this will serve to 'excite' the pattern of ridges and troughs ]resulting in height rises over Greenland.

    For my money, we are likely to continue with the pattern of ridges and troughs that we see now, possibly with a hint that the last week of the month will start to to take effect;the impacts of the stratospheric warming with decreased momentum leading to a northward shift in the ridge with split flow. I have more confidence in more progressive blocking taking place during March. Organisers of the Cheltenham Festival (mid March), take note.

    This statement has been typical of both you & john all Winter long & has lacked clarity for some of the regular posters on here ( the less seasoned ones shall we say)- you have both been touting this - through the GWO composites & John with the CPC model outlooks, however Height rises over Greenland cannot be compared with a true Greenland High-

    It would help if you would clarify what your expecting- As I would put the correlation with the Current Pattern & a Greenland High developing pretty close to Zero, however the height rises typically seen over Southern greenland with the transient ridges coming out of the atlantic are different & slightly more achievable, although just as unlikely at the moment to be sustained for more than one day especially with the GLAAM levels decreasing-

    For whatever reason the net effect thus far of the warming has been minimal, maybe more prevelant at 70n, but not at this lattitude- I suggest whatever propergates down now will not arrive with the big bang as some expected, but maybe having a weaker effect on the Westerlyness of the zonal wind-

    I did suggest on more than one occasion to John that the CPC charts were going to be wrong, but the secondary replies I gave to his responses must have been overlooked-

    Winter is Over- move on- get over it- the sustained cold never came ( surface stagnent surface air doesnt count)

    March may herald some more snow- but it not the same-

    Stewart- instead of posting the GWO composities of what we are seeing now ( & likely to be in the short term)- maybe post the 500mg Height anomalies for what your expecting day 7-10 or 10-15, at least thats a forecast then -

    S

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    It would help if you would clarify what your expecting- As I would put the correlation with the Current Pattern & a Greenland High developing pretty close to Zero, however the height rises typically seen over Southern greenland with the transient ridges coming out of the atlantic are different & slightly more achievable, although just as unlikely at the moment to be sustained for more than one day especially with the GLAAM levels decreasing-

    For whatever reason the net effect thus far of the warming has been minimal, maybe more prevelant at 70n, but not at this lattitude- I suggest whatever propergates down now will not arrive with the big bang as some expected, but maybe having a weaker effect on the Westerlyness of the zonal wind-

    S

    Morning Steve.

    Readers of this more technical domain do so under the understanding that the terms used maybe different, and this may from time to time spill over into MO thread. Reanalysis of the H5 field anomaly for the last 90 days shows a weak to moderate strength positive anomaly over Greenland and a stronger one centred in the Atlantic.

    This is different to you spell binding Greenland High yes, but see the caveat. Moreover, there has been two episodes this winter that have featured significantly greater positive anomalies - over Christmas into the New Year and 1st week February. The former was a good example of retrogression from Scandinavia. I would therefore maintain that references by myself and John have been correct and appropriate.

    Winter is Over- move on- get over it- the sustained cold never came ( surface stagnent surface air doesnt count)

    I'm interested in the application of the GWO as a long rang forecasting tool. I will be here during the Spring, Summer and Autumn hopefully adding positive contribution.

    Stewart- instead of posting the GWO composities of what we are seeing now ( & likely to be in the short term)- maybe post the 500mg Height anomalies for what your expecting day 7-10 or 10-15, at least thats a forecast then -

    Steve, read my thoughts on where I think the GWO is heading within the extended range - phase 1-2-3 orbits, probably remaining in a quasi-stationary orbit around phases 2/3 as the atmosphere plunges into deep negative momentum territory for March. The composites spell out what likely pattern (in terms of H5 anomalies) to expect.

    Updated mountain torques show a sharp decline over Asia in particular.

    http://www.cdc.noaa.gov/map/images/reanaly...ltaum.90day.gif

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    March may herald some more snow- but it not the same-

    In what way is it not the same?

    If you are talking about sustained snow cover then it is harder but other than that I find the comment slightly ridiculous. There have been some remarkable March snowfalls in the past.

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    It seems to me that Steve has been affected by the seasonal switch! I.e. once we approach the beginning of spring we should forget snow and cold, and seek warm sunshine.

    Last year, we received the best snowfall in March and April, so that in itself makes it worthwhile to continue to look for wintry weather in the models.

    As for snow that lasts for days or weeks, well that's unusual in lowland Britain at any time of the year, yet this year we achieved it despite not particularly 'favourable synoptics!

    Karyo

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    Only just noticed the post from Steve and the comments from GP (Stewart)

    First let me say I've never done any other than repeatedly, if anyone reads my lrf outputs, said anything other than its a new area to me. I find it fascinating trying to give a general idea for 2-3 weeks ahead. Like GP I'll be here Steve, through the whole year, God willing, to carry on, as I did through the whole of last year Not just Winter, trying to improve the lrf idea, trying to learn more about the topic.

    I thought I had said enough times that no single link is the way to forecast, you have to look at every item that may impact over the time scale you are trying to forecast for. That is what I try to do. I try not to be selective. I try to post things as I see them honestly and I'm pretty sure my lrf's over the past 13 months show that. I continue to believe that, be they CPC charts, ECMWF hemisphere charts, Stratosphere input, ENSO etc etc, all have a part to play and all of us, I hope, accept that we are learning. No one gets it right and I've already put my hand up regarding the prediction of deep cold by now. I have been forecasting for far too long to be afraid to say I got it wrong.

    All of us have something to contribute to this forum so lets just do that and not, as winter (officially) draws to a close get a bit niggly with one another.

    As, I think most of you would find, if you apply the Mr D winter index for the station nearest you, many of us have had a fairly memorable winter in terms of length of cold, some even for extremes of cold, and some for length of snow on the ground.

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    It seems to me that Steve has been affected by the seasonal switch! I.e. once we approach the beginning of spring we should forget snow and cold, and seek warm sunshine.

    Last year, we received the best snowfall in March and April, so that in itself makes it worthwhile to continue to look for wintry weather in the models.

    As for snow that lasts for days or weeks, well that's unusual in lowland Britain at any time of the year, yet this year we achieved it despite not particularly 'favourable synoptics!

    Karyo

    Amen to that :D

    Don't want to derail this very good thread, there are too many threads open at the moment lamenting something that shouldn't be lamented. The factors that are being monitored on this thread, and in conjunction with the strat thread are still very much there. Even if there continues to be a stalemate in the models atm. I am very interested in how the start to the coming Spring plays out. I can see a very easterly and northerly dominated one with all the interest that that entails for our part of the world.

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    Current Analysi of the stratosphere.

    5 Days out.

    From this I would take a strong signal for blocking in the northern Pacific and a secondary weaker signal for blocking in the north Atlantic. This kind of shows up on the GFS blocking maps.

    8 DAYS OUT

    How does it compare to ECM and GFS forecasts.

    Clearly the strong signal is across the other side of the world and we are more likely to be influenced by GWO and as a downstream product of the strong signal in the pacific.

    GWO is now headed strongly into phase 1 and there are clear indications that Global Angular momentum is likely to tank. I see this as an indication that we are never going to be far away from being north of the jet stream, but indications are that we might just miss out on the really cold stuff. Spring weather with a misture of cold and mild seems in order.

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    I must admit to not understanding fully the implications of all the different teleconnections and how they interlink with one another. I'm sure i have read in past posts how a rising glamm is good for blocking then next i read that a sinking glamm is what you need,so at times very confusing.

    Last winter the glamm went through the floor and we all know how that turned out, although whether that was from the glamm or cold stratosphere and strong vortex i don't know.

    Could someone explain what the GWO is in relation to the glamm, mountain torque and friction torque, i think thats the lot.

    I was under the impression you needed angular momentum to mix with the polar westerlies which would disrupt the zonal westerlies adding warming and blocking at higher latitudes.

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    You may have thought that snow meant snow. We know from the train companies there can be the wrong type of snow and in other languages, there is a wide variety of descriptions for snow forms. It seems within the betting world what counts for a White Christmas is also quite varied.  Frozen Precipitation - that's what it is all about... Read the full article here: https://www.netweather.tv/weather-forecasts/news/8573-wintry-showers-and-what-counts-for-white-christmas-observations  

    Paul
    Paul
    The Basics
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