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Catacol

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Catacol last won the day on January 18 2016

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    Wellington, Somerset
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    History, Rugby, Cricket... and snow. World of Tanks ain't bad either.
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  1. In simple terms the equatorial Pacific is the engine room of the entire global weather system. In a Nina the cooler waters encourage less convection and hence less storm activity and this in turn means there is less energy transferred to the northern hemisphere circulation. With less energy this tends to suggest waves of lower amplitude circling the earth... and without sufficient amplitude we end up with a flatter pattern. For us at 55 degrees we are then in a poor position because the normal position of the jet stream will tend to fire systems straight across the Atlantic at us in winter. For a higher lat block to be encouraged to take hold we need a more “wobbly” wave pattern courtesy of Pacific energy and atmospheric momentum. The current Nina pattern is centred in the eastern Pacific. Pacific convection begins in cycles much further west than this. Those who are forecasting opportunities for cold later in the season are hoping that convection anomalies in Indian Ocean and central Pacific will produce forcing that will be sustained as the convection pattern moves east despite the cold waters in situ currently off Peru. Others think those cold waters will neutralise the pattern just when it hits the crucial eastern Pacific sector which is particularly important for blocking in our part of the world. I am hoping Nina may fade just as the next cycle (MJO) begins, allowing a crucial input of energy into the system in the heart of winter. The next MJO cycle ought to begin in mid/late December, perfect timing for impacts in mid Jan. But if Nina strengthens.. and the atmosphere has already coupled to the Nina signature that will encourage flat westerlies across the Atlantic, then we will struggle to get blocks high enough. Azores High, or Euro High, influence will likely grow and then our winter sags. The same Pacific forcing also has an impact on the stratosphere via potential vertical wave breaking of warm air upwards. This is another complex situation, but to maximise the benefits of the next Pacific cycle it wouldn’t be w bad thing to see an aleutian low in the North Pacific coupled to a Siberian High. These 2 features, properly positioned, can encourage vertical wave activity by adding energy to the atmospheric circulation via mountain torque and also disrupting the intensity of the vortex by firing broadsides of warmer air into the vortex as part of the torque event. I struggle to visualise the mechanics of this in all situations because these warm air attacks can disrupt the vortex in what seems to be a myriad of different ways, but once disrupted lower zonal wind speeds can also aid in blocks becoming established at high latitude. Long and short of it is that the Pacific is absolutely key to patterns of weather in the North Atlantic. The obvious final point is that an incorrect seasonal assessment of Pacific patterns means any seasonal forecast for the UK ends up inaccurate. The reality is that the Nina forecast is not carved in stone and therefore, if the starting pacific conditions are incorrect in model calculations, then no matter how great the computer power the resultant forecast is damaged. UKmet forecasts of Nina are on the strong side compared to ECM at the moment, and I think this is important when considering Glosea output. But the last 3 Glosea runs have sequentially suggested less mild and more potential for cold... though the probability maps still suggest mild more likely than cold form the coming season. My interpretation, for what it is worth, of that trend is that all models are seeing a relaxing of the Nina signature as we hit January and so chances for blocking in mid to late winter may be gently increasing. However this is all conjecture at this stage really... but to finish with a direct Nina comment: if we want decent chances of proper cold in mid winter it will help if Nina doesn’t drop too deep.
  2. Yes - and the longer the “hurrying up” is delayed the better it will be when the next cycle of Pacific forcing begins. It’s only Nov 18 and it feels like winter has been underway for eons - so much discussion and focus! It really is early days and sooooo much patience is required.
  3. That’s my reading of it. Low pressure moving to the west of the Himalayas while high pressure moves further east causing transfer of energy to the atmosphere via mountain torque and consequent vertical wave activity.
  4. This is rather interesting. Need more updates - but that green line shouldnt really be heading towards the 5-8 orbit in a Nina state. Shows the ongoing disconnect between ocean and atmosphere in the pacific helping sustain a global pattern that is generally disconnected. Is this the east based Nina with neutral tendency in region 4 sustaining some amplitude? Vortex repositioning to Siberia also set to create a bump in AAM via himalayan torque in tag team effect with (probably temporary) appearance of low pressure in the north pacific and a bit of US driven torque also. Nothing to jump up and down and be hugely excited about yet.... but stuff like this shows that interest is to be had in the extended period especially if the disconnect can be sustained as long as possible thanks perhaps to the current shape of the Nina pattern and the slow start to the season for the tropospheric vortex. It would be gold dust if the next MJO phase could begin while that disconnect were still in force - I'd start to be become properly excited in the possibility of some mid to late winter blocking setups if that happens... ... but we wont know that for a while yet. Could still see a Nina pattern and a wimpy MJO bumping up against an established trop vortex. All to play for. Still think December will be uninteresting for the most part.
  5. Accurate I think. Modelling of the jet over the Pacific has been all over the place too recently, and this has helped create huge model uncertainty, but what we can see clearly is low AAM, no MJO influence yet (probably 4 more weeks away), a Nina pattern taking hold (uncertainty on how long it will take to couple effectively to the atmosphere) and the vortex predictably gaining strength. The decoupled state of ocean, atmosphere and vortex at present will allow variations from a Nw and Sw direction with a jet that will look anything but flat for a bit longer yet, but without proper Pacific forcing the chance of a substantial block to our north setting up shop is slight. We may get temporary topplers, and I suspect a good start to the Scottish ski season my be in the offing with plenty of NW shots - but lowland snow via sustained cold in the south just doesn’t look likely to me. From here the odds are in favour of a move to a more zonal December. This may be delayed by a week if the trop pattern can stay disconnected a while longer - Ant Masiello has suggested this is possible - but westerlies by mid December are probable. Patience is required. The chance of a change to something much more interesting sits with the next MJO cycle (possibly aided by a resistance to Nina anomalies in the central Pacific) and hopefully a Nina that doesn’t bottom out too low and perhaps begins to wane in January. This could create interest via vortex disruption and renewed pulses of energy into northern latitudes that could possibly aid in creating a blocking pattern. This is a January conversation. Right now I’m happy with a few frosts and a fairly benign pattern with westerlies slow to take hold. But I think it is only a matter of time until they do. Anyone heard from GP recently?
  6. 2 very different forecasts. I'll take No2 please. Their interpretation of the NAO signature could not be more at odds!
  7. Yes - continued concern on the depth of Nina. MetO forecast a few days ago caught the eye, and with region 3.4 already at -1.2 and forecast to fall further we could end up in -1.5 or lower territory. Hard to see much AAM coming from such a setup. A winter of topplers only?
  8. I think you are spot on here. Much will depend on the next MJO cycle late Dec and the extent to which Nina has taken hold. By late December it seems likely the current strat/trop disconnect will have ended with westerlies descending from the upper strat and taking hold (no signs of an early season warming at this stage) and unless something changes soon a zonal December looks increasingly likely. If we don’t get decent tropical forcing from the next cycle then High lat blocking will be hard to sustain. But these remain ifs and buts at this stage. Long way to go. As we saw last year early building blocks and supposition based on November conditions can soon turn around. Cohen implied as much yesterday and plenty of other experts across the Twitter sphere are hedging their bets at this stage. Anyone heard from GP recently? I know he cannot give away too much these days, but his interpretation of conditions over the next 3-4 weeks would be interesting and valuable.
  9. Agree with all of that. MetO forecast trend is towards a deeper Nina though - in this case I hope the trend isn't the friend. SOI all over the place this year so far though since June again the trend is quite clear Looking for that trend to halt soon.
  10. Quite a good graph here. However - for analog junkies - Alan Huffman has noted that the PDO is in weak positive phase and based on a positive reading since Jan 14 may well stay that way. The analog years for a weak Nina (if it will hold as weak) with a +PDO are 1962/63, 1984/85 and 1995/96. Suddenly doesnt seem so bad when reading it that way.. :-) He also correctly points out that regions 4 and 3.4 are less Nina like, and perhaps this will aid in a more active MJO phase come late December than we might normally expect in a Nina year.
  11. Nina is only one factor, but if it does drop to -1.5 then analog years would tend to suggest it will over ride any other signal and produce a westerly, wet and perhaps above average mid to late winter. However, as already stated, it may not drop so low... and it may begin to trend back to neutral just as a new phase of the MJO begins. Much still to be resolved. For my own part the Nina forecast has tempered my expectations. Low expectations may be just the right way to head into winter and enjoy any surprises that might occur! In the near term we have an ongoing Trop/Strat disconnect and residual effects of a fairly potent October MJO creating a -AO. Let's enjoy what comes - if it comes...
  12. Latest Metoffice update has the 3.4 region dropping to -1.5 or maybe lower... though some members are less cold. This isnt good. Takes Nina forcing into 1988/89 or 1998/99 territory.
  13. 95/96 bottomed out at around -1. Bulk of the Metoffice members are seeing -1.5 to -2. Not the same. 88/89 and 98/99 both had Ninas in this bracket... and none of our more famous winters have occurred in Ninas of greater than -1. The only exception was the early cold we got in Dec 10 but the strength of the Nina that year soon put an end to the cold. Chio's call of front loaded cold (if we are to get some) would seem a good call at the moment. We may need to make the most of what is coming in around 10 days' time and hope that the strat/trop disconnect can continue as long as possible. But hey - funny things happen. The Nina could begin to wane quicker than expected and trend back towards neutral, and then the next MJO phase later in December might possibly have enough grunt to force some higher lat blocking. Only time will tell... but I will be watching Nina development over the next 4 weeks carefully. If it continues to deepen right through to Xmas then..... :-(
  14. Not especially important in a thread looking at winter hopes. I had hoped we might see Nina fade but in reality it seems to be gathering pace. It is a blow to hopes this winter for cold in Jan/Feb - but perhaps we can see better fortune develop later. Fine margins count for much in the UK and topplers can produce at times. Glosea update appears to be in tune with the Nina forecast. Chances of a westerly dominated winter once strat and trop couple in December have increased today.
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