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Catacol

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Catacol last won the day on September 11

Catacol had the most liked content!

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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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    Frost and snow. A quiet autumn day is also good.

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  1. These anomaly charts need to be taken with a dose of common sense because they tend to mask actual synoptics - but the idea that there has been a semi-permanent winter high in the SE of Europe since 2012 isn't borne out by the data. Taking 2012 - 2017 in turn there are 2 with above average pressure in that region through winter as a whole, 1 about average and 3 below. Winter 2015/16 was certainly a +NAO horror show.
  2. For those who place emphasis on pacific cycles that rise and fall in approx. 10-15 day phases it is no surprise to see the blocked pattern come under a bit of pressure. Calculated overall tendency of AAM has fallen after the October rise that brought blocking - but the steepness of that fall has been a bit of a surprise (to me at least) The collapse in atmospheric momentum you can see clearly has been steep. This is mirrored in the decline of mountain torque in the same period. The result in the atlantic is a move towards a flatter profile and no doubt storm Oscar has help invigorate the atlantic trough to the point where mild SW winds are now forecast. However the overall pattern globally is anything but flat. Note the resilience of the Euro block (continuing to aid in potential future vortex stress) My call of blocking through to mid month now appears a bit optimistic as this ridge is likely to wane from here, a few days early. But what of the end of November and into December? Note the fairly strong state of the current MJO cycle using Ventrice's useful graphic, and an MJO signal passing through phases 7 - 8 - 1 (remember Snowy Hibbo's call of this being a feature through the season) aiding in retention of a signal for blocking. Returning to the cyclical nature of the pacific we can be sure that the steep decline in relative tendency will bounce back up fairly soon as frictional and then mountain torques reengage. The question is - just how high will momentum bounce up? Given the resilience of the Euro block, and ongoing weakness of the trop vortex, I would guess that even a moderate rise in GLAAM tendency will be sufficient to reinvigorate the blocking pattern given usual lag. I am a lot less confident about picking the exact location of where the block may reemerge, but given the arrival of the east US trough that was discussed a while back I'll take a stab at a retrogressing signal that pulls heights back west from the current European zone, leaving us on the colder side of the block. So I don't think the warm atlantic trough is going to be here for long given the current state of atmospheric momentum and the pacific cycle. Latter third of November to be blocked and chilly once again. And December? The biggest player for me longer term will be the stratospheric vortex and its ability, or not, to descend and tie the troposphere to it. GFS forecasts for substantial invigoration towards month's end are in place - but frankly the sudden transformation of stratospheric forecasts last winter leaves me very suspicious of any attempt to predict vortex impact at a month's range. Personally the longer the Euro high that many on here are irritated at hangs around the better for me, because it increases the chances of distressing the vortex in the longer term via warm air advection into the pole and vertically into the stratosphere. By the start of December we are sure to be seeing the impact of the next drop in GLAAM tendency (back to the pacific cycle again....) but in a Nino year if the vortex remains decoupled and we don't get another Oscar thrown into the mix then there is every chance of the block holding on. Can it remain high enough in latitude to bring sufficient cold for lowland snow? My gut feeling is that we will need to see one more rinse and repeat pacific cycle before this happens....so I'd guess at a return of some atlantic influence into the start of December but in a context that is still rather blocked. So temperatures moderating but not raging zonality. Having said that, atlantic energy in December with blocking around can lead to stalling systems.....and rainfall totals in this scenario can be high as we have seen already this autumn in mid/south Wales. Lots of interest in snow cover, QBO influence, ENSO profile, upper/lower vortex development, MJO strength and phase still to come as we approach winter proper. For sure, however, there is enough potential in the background signals at the moment for all hunting for cold to be optimistic. Great to be entering 3-4 months of core winter wonderland hunting once again.
  3. Catacol

    Winter 2018/19

    I agree that our meridional 2018 is continuing - a distinct lack of dominating westerlies for a long time now. Spotless days and low geomagnetic influence do seem to correlate with colder winters and when one aligns this with current ENSO and signs of Siberian high / Aleutian low combo in the wings we certainly cannot complain as to the background signals at this early stage. Even Siberian snow cover has made a late surge, prompting Cohen to tweet enthusiastically. I'm not seeing anything at the moment pointing to a strong atlantic waiting in the wings. If we had a descending eQBO rather than a wQBO we would be in near perfect territory...but by the time we get any substantial wQBO below 30mb I suspect it will be too late to impact on developments for the core of winter. I'm also feeling optimistic about this winter, though I've been burned enough times over the years to be cautious. I'm expecting a generally blocked pattern to sustain itself (temporary incursion of Oscar excepted), and if we see the vortex remain disorganised at lower levels and that Barents/Kara ridge stay strong in through the second half of November then it might be time to get properly excited. Low solar is certainly going to help in holding back the vortex, that's for sure.
  4. This is a little more up to date. Looking neutral at present. http://research.jisao.washington.edu/pdo/PDO.latest.txt
  5. True enough - its a risk. Given the temperature gradient that looks likely to form off the east coast of US/Canada we'll be lucky to avoid at least one substantial period of cyclogenesis. However the picture is a bit more complicated than this - much depends on the passage of the jet as it moves through the American continent, and this is determined to a large extent by what is happening upstream in the pacific. Weak Nino may help prevent a flat pattern firing out on Canada, and we are all watching the development of the vortex carefully. Currently up at 10hpa it is building well, but at lower levels is still rather disorganised. It would require a number of factors to come together at once to create the nightmare +NAO flat and wet atlantic that many of us dread, and I think there is grounds for optimism that this wont occur this year. (famous last words....)
  6. We are 6 - 8 weeks too early - but after a rather Nina-esque fall in GLAAM we are now seeing a steep rise in the calculated overall tendency This early season mid atlantic ridge scenario produced off the back of the fall should be replaced by a much more meridional pattern conducive to the high lat blocks that we so crave in winter. EPS shows this well at 7 days' range Where after this? It's still a bit early to get excited to be honest - charts like this in late December would offer snowfall to parts of lowland Britain but right now it is too early. But with the MJO passing through phases 8-1 I'd take a stab at the rather blocked pattern continuing through to mid November.
  7. I don't think we will be as amplified as this quite so early - but I think this kind of chart has a decent chance of featuring this winter season, given the combination of background drivers in place. For early November I think the high a bit flatter with the jet curving over the top - but a month later? Not impossible.
  8. Yep - don't disagree with these options. I've just been musing elsewhere about what causes core features to embed over a season or part season...and my initial thoughts are more around the -EPO and NNE jet at least for the next few weeks. With Nino gradually increasing in strength and appearing to harness a high GWO orbit plus low solar/sluggish? vortex start, I wonder what our chances are of seeing sufficient amplification later on for a scandy high to enter the frame with a fairly constant retrograde signal? I'm hoping for the holy grail there (might even see a Murr sausage appear...) but we have to acknowledge that low solar, weak Nino and inconclusive QBO (would be great if the eQBO could hang a bit in the mid strat) gives us a very positive background signal. We certainly aren't looking at a raging Nina alongside a major wQBO and lots of solar forcing! All good. Glad to have seen the back of summer - didn't like it at all. Fingers crossed for white gold soon, even if it is bound to be the northern brigade that see it first |-[ Any cold initially from the north to start with, and later into January more from NE and E. That's my current call.
  9. Thanks Snowy - yes - this is my take on RJS's early season descriptor and on the pattern as I see it related to the current shape of Nino and AAM trends. Beyond November is really tough at the moment: we dont have a handle yet on the vortex (though Recretos' diagramme in another thread is really interesting, suggesting 2 key long range models seeing a warming again...) and for followers of Cohen's theory it is also 2 weeks too soon to draw a conclusion. A mid atlantic ridge giving us some frosty conditions into November would be a good start. I'm not particularly keen on the idea of November snow - I've only ever seen it once in lowland England close to me (and it was the last few days of the month) and it lasted less than 36 hours. Let's not waste good synoptics on November! Mid December following a continental cooldown is the start of the sweet spot.. :-) Steve - I hope you are having a better day today!! All I posted yesterday was a personal opinion based on a starting point of Roger's strong sense that a cold start to the Canadian arctic season is likely to produce a downstream cold East US trough and from there a mid atlantic ridge under high AAM conditions supported by Nino and a high orbit GWO. Let's see if it transpires that way. If November doesnt pan out that way then we havent lost any of the "real" winter season...so everyone stays happy..
  10. At 10hpa you wouldn't expect to see much else. Note the 10hpa strat charts in Feb 2018 when we were experiencing our mighty warming and eventual split lower down The key to the charts Recretos has posted is that we have an ensemble mean signal for a warming over Asia. That is good news if strat disruption is what you want.
  11. Catacol

    Winter 2018/19

    I think for now the most I am prepared to say about the long term (December onwards) is that the signal for a winter with a strong azores high presence looks rather weaker than most recent years. Nino wont help the azores high for sure, and the ECM probability forecast for sea level pressure suggests a year when we wont be plagued by high pressure bumping up from the SW. This is a long way away from suggesting an automatic high lat block and cold continental air source BUT it is a start.
  12. Half way through October. Time to stir.... Interesting reading RJS's comments in the seasonal forecast thread regarding extreme cold in central Canada and likely downstream trough from this event. If this can be given as a base state heading into the start of winter, then exact positioning of the long wave pattern becomes guessable. Note the MetO ENSO forecast As many forecasted several months ago we are heading into a weak Nino winter with consequent pressure applied to subvert sub tropical high pressure belts and therefore the possibility of a more southerly tracking or split jet. GLAAM is in a moderate to strong positive phase and the Nino imprint onto the atmosphere is clear from the GWO state which has been locked into the 5 - 8 orbit for weeks now For the foreseeable therefore a pattern that wont encourage flat westerlies, should instead see a good deal of jet wobble and curve, and an autumn that for now looks to remain fairly blocked. With an eastern US trough likely then the suggestions from a number of posters that a mid atlantic high may develop downstream looks about right to me in the context of the above. That might help to bring about a frosty and foggy passage into November.
  13. A spike or rising AAM at the tropics will tend to inject a westerly wind burst and help cancel out the trade winds at the equator. This in turn undermines the strength of sub tropical high pressure belts causing them to retreat south. High momentum at the equator is then balanced by lower momentum at higher latitudes. Therefore when we have higher relative momentum readings at the equator it is a decent precondition to blocking at our latitudes as the jet meanders under reduced momentum conditions at our atlantic latitude. This diagramme does it for me - shows the Hadley Circulation and corresponding balance given to global momentum budgets. Colour contours on my first image between 30 and 60 degrees tend to represent torques applied by the Tibetan Plateau (at about 30 degrees) and the Rockies (closer to 45 degrees). All mountain ranges can apply torque...but these are the big 2 relevant to the northern hemisphere.
  14. Not quite yet - pressure patterns from around the 12th suggesting the possibility of a trough dropping down to the east of the Euro high and perhaps setting a precondition Certainly no torque event happening right this moment - Masiello is just getting excited. If it comes as is possible it will produce +AAM that will help continue the current meridional type circulation. At the moment the most obvious thing to report is that we have some sustained positive relative AAM in pulses, sustaining that meridional jet and more N/S rather than W/E influence. Way way to early really to draw any conclusions from this as we wait to see just how high Nino may push and just how the trop/strat vortex couples up and any sense of sustained pressure patterns. The current Euro block over Scandy would be good news later in winter for setting a precondition for vortex disruption, but not much point getting too excited about such things until we get to November. Cohen's October snow advance theory is an interesting one to keep an eye on at this time of year, but it isn't really a guarantee of anything. Bottom line - too early to risk any kind of forecast.
  15. Current snow levels are less than some years - but not especially unusual. Run the link that interitus has given: there are other years with more red. In essence the loss of so much sea ice is going to make early autumn mild because it takes that much longer to regain ice coverage. Temperatures will be higher. Does this impact on the depth of cold in Dec/Jan/Feb? Good question. Data for midwinter would be interesting.
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