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Catacol

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  • Gender
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    Wellington, Somerset
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    History, Rugby, Cricket... and snow. World of Tanks ain't bad either.
  • Weather Preferences
    Frost and snow. A quiet autumn day is also good.

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  1. Seems like the right thread for this musing... Tropical atlantic SSTs have gone cold at the moment around the western edge of Africa. In many years on this forum and others I have rarely seen much discussion of the impact of tropical atlantic temperatures. Is there anyone out there with papers or thoughts as to potential impacts in the north atlantic basin?
  2. I don't think little troughs change patterns. The key to what is happening this week - and was forecast to happen - is the impact of the westerly wind burst out in the Indian ocean that began soon after 13th June. This was part of the MJO in its current cycle Given 7 - 10 day lag effect of a shift like this we are seeing a greater signal for Euro heights and the trough has pulled back west. This is a symptom of an enhanced pacific jet with consequent buckling of the pattern at higher latitudes. In winter it is often what we look for in the hope of seeing a ridge forced to northerly latitudes. Given the wind burst lasted over 10 days I think we can expect a more high pressure dominated scenario throughout this week and into the start of next. The tricky bit though - as you can see from the forecast chart above - is that the westerly burst hit the buffers before getting much past the maritimes. and already the trades are pushing back and are forecast to all but wipe out the westerly burst by month's end. Given a 30-60 MJO cycle, and it has been travelling more on the slow side than quick side of late, we can perhaps take a stab at the next westerly burst not arriving for a while. What does this mean? Pacific jet weakens, and as a result under conservation of AAM we can expect the pattern at our latitude to flatten back out. But this is very simplistic, and often hides small details that for our locale are crucial. For me what will be vital as the pacific resets is just what happens to our north. Throughout May and for much of June we have had a resident HP signal over Greenland. Will this return and the jet be forced far enough south as the signal for Euro ridging fades to give us a return to something rather "average" - or can we achieve a more +NAO pattern and hope that the westerly pattern at least avoids the south of the country? Jury is out...but as I've said before I have a nagging feeling that the pattern might reassert. This FI GEFS anomaly chart might just be the beginning of the process I'm describing - trough returning to the vicinity of the UK as higher pressure is forced back west and possibly NW. We will see. For now - all hotties (let's agree to use that word a bit more ) should try and enjoy the week to come. For me the interest will be just how many storms enter the mix as instability should be a factor throughout the week at various times, and by next weekend we may have more of an idea as to whether we get a reset with a Greeny high forcing systems back over the UK, or whether we can retain enough high pressure to deflect things to the north under a more +NAO regime. To that end this may be relevant - shift in SSTs around the UK and to our SW more conducive to supporting the Azores Ridge. Mediterranean also warming up. However notice the more -NAO appearance of the SSTs out in the west atlantic, also suggestive of a possible return of the Greeny High. July in the balance?
  3. Cant be bothered to do a proper count in detail right now - but what's interesting also is the apparent bunching of -NAO months around moments of the last 2 solar minimums. A lot in the 2008 - 12 bracket. A lot in the mid 90s. Not so clear to the naked eye in the 80s. But if low solar does indeed impact on the jet and perhaps pushes it south, then we can expect another cluster of -NAO figures over the next few years. Perhaps if I get bored over the weekend I'll do a tally of NAO signatures against solar cycle. I expect someone has already done it...but playing with stats and figures is always more enjoyable than just reading them...
  4. Yes - I'm sure at some point in the past there was a MetO article discussing SSTs and linked pressure patterns in May with the winter to follow. Does Gav Partridge not discuss May in his thinking?
  5. Ha - totally agree. Stats can prove anything. And yet we are yet to see a mild winter follow a very negative and blocked May in the last 78 years. Cue the year that now breaks the pattern....
  6. Fun facts - because we all know I'm only really waiting for the next winter to arrive. May 2019 was extraordinary for one factor in particular - namely the depth of the -NAO. After what felt like a never ending spell of +NAO setups for the most part (only 2 x -NAO months since end of summer 17 until we hit May this year) we hit a very low figure of -2.62. This is the lowest recorded May NAO score on NOAA records going back to 1950. Cross reference this with seasonal impacts going forward. There is a theory out there that the NAO setup in May is an indicator of patterns for the following winter. So - which years had a May NAO of -1.5 or less? Answer: 2017, 2010, 2008, 1995, 1990, 1980, 1968. Common theme here? None of the following DJF CET scores were higher than 1.6 and all bar 2 (1980/81 and 2017/18) were below 1. Just saying....and most definitely not a winter forecast.
  7. Not read the forum in recent days, but the obvious observation tonight is that northern heights are not fading for long, and we have another possible cut off low appearing as we move forward into medium range with the UK in the firing line for more atlantic traffic. Signs too perhaps on the GFS equatorial forecast that the predicted/current burst of westerly winds may not last long, and a hint at the return of a Nina style dominant Trades' scenario by month's end. So the better spell of weather will arrive shortly, but frankly no obvious sign yet that summer is here to stay. That sneaky feeling that recurrent northern heights are going to continue grows. A stagnant standing wave and a pacific that has never quite woken up to the Nino signature that in theory it has sat under for a good while now is a key contributor. And while it is not a certainty, the likelihood of a dry, warm and sustained "good" summer decreases while heights to the north serve to deflect atlantic energy south of Iceland. Notice also the SST pattern currently - cold blob in the western atlantic sat south of warmer seas around Greenland. -NAO style pattern with the oceans around the UK and Western Europe also now doing their bit to push away any nudging northwards of the Azores High Might be worth looking for a holiday outside the UK this year and before Brexit Trauma takes hold properly.... Having said that - and a phrase we use a lot for obvious reasons - still time for a change! 2 months of calendar summer left yet.…...
  8. Thanks Malcom. Relevant here is this article also - can both coexist happily? https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-14-00632.1 From the summary: "To first order, the magnitudes of the meridional potential temperature gradient and of the mixing length determine the synoptic potential temperature variance near the surface in midlatitudes. Arctic amplification of global warming leads to a reduction of the meridional potential temperature gradient that is expected to be larger than any changes in mixing length (especially in winter), leading to a reduction of the synoptic potential temperature variance near the surface." and "Idealized GCMs and comprehensive climate models robustly show that the synoptic potential temperature variance indeed decreases in midlatitudes of the Northern Hemisphere as the climate warms, especially in winter (when Arctic amplification is strong). Most of that variance reduction can be attributed to a reduction of the meridional potential temperature gradient, consistent with the findings of Screen (2014). But changes in the mixing length and other processes also play a role." and "Taken together, these findings indicate that Arctic amplification of global warming leads to even less frequent cold outbreaks in the Northern Hemispheric winter than are already implied by a shift toward a warmer mean climate. We did not examine specifically how the frequency of blocking episodes changes with climate (cf. Liu et al. 2012; Hassanzadeh et al. 2014). However, our analyses suggest they do not modify synoptic potential temperature variations and/or their departures from Gaussian statistics substantially."
  9. An improvement is certain now, and given flooding impacts of what has come this week a change is most welcome. Many of us here enjoy extreme weather events at different times of the year, but I don't think any of us enjoy seeing lives negatively impacted in this way. Last third of June should see much more in the way of a neutral to positive NAO signature which will allow high pressure to impact from the south from time to time but also with opportunities for the odd damp blip. In this context average temperatures a decent bet. Taking a peek into July and I notice 2 things: a GEFS ultra extended that hints at the return of northern heights as the pacific wave fades, and secondly a MetO report rather in line with that GEFS prediction. Summer 2019 kicking off in a dramatically different style to 2018. Ebb and flow of a pattern setting up for the season? I had thought an improved end of the month might last long enough to encourage warmer air to the south to intrude for a bit and give sun/warmth lovers something to enjoy for a while in early July - but not quite so sure now. If Griceland heights build back again then chances of warm and dry fade. In the meantime as things gradually improve trough impacts look likely to continue to have some degree of impact for another week yet.
  10. That's a really interesting abstract - and certainly reflects the frustration from some learners (me included) who have consistently expected momentum spikes in recent Nino years to produce a bigger trop and strat response to resultant momentum spikes. We know that our Beast of March 18 was nicely setup by a resilient East European high in a weak Nina year that provided the setting for the remarkable spike in flux - and the consequent favourable destruction of the vortex (favourable that is if you like UK snow...) The bit I like less is the final sentence that smacks of white flag raising. "The anomalies in the East European sector in response to ENSO likely reflect unforced internal atmospheric variability." Hmmm - ok - maybe...but that is a pretty uninspiring sentence that effectively translates as "we don't know why...." and so we return to observational learning. And observational rather than model based theoretical learning might be the way to go. On a personal level I found the winter just gone a pretty sharp kick to the sensitive parts of the interested intellect. Masiello summarised the failure of the expected atlantic pattern to shift to high lat blocking as the fault of SST anomalies. Maybe he is right. Maybe - on top of that - we have to accept that our weather no longer behaves as past data suggests. Plenty of others have suggested this in recent years, and we have to acknowledge a degree of remarkable extreme variability in recent seasons that is not expected. I might be guilty of over reading things...but the current cold and wet spell in June seems remarkable. February was very warm. Last summer was very hot. March 18 was remarkably wintry. Is this all natural variability or are we simply in a different world now with regards to forecasting weather and its impacts? B*astardi constantly argues that all this has happened before within the last 150 years. Is he right? None of us has an accurate window into the early years of the 20th century to really know....but to my eye things are not as they were 20 - 30 years ago for sure. Arctic ice for sure is retreating significantly now. So - I'm watching this summer with more interest, and my own approach to the next winter is going to be much more circumspect and thoughtful. My own belief is that patterns are changing and atmospheric responses are going to continue to get more extreme. At a macro level this is a huge global challenge....at a selfish micro level this must means greater localised uncertainty and consequently enhanced enjoyment in observed impacts.
  11. Probably difficult to do anything other than improve from the week we have now - but Crewe has it right: change from poor to average. Strongly -NAO to be replaced by trough to our west and ridge to our east looks the likely development...and this will bring temperatures back up to average and possibly a bit above average at times, but I doubt it will keep things settled for any length of time. GEFS has quite a pronounced signal for a trough just off to the SW in the extended, and the high pressure anomaly over Greenland has not gone altogether - so a very very different setup to last year. Azores High not a major player yet. Given that modelling often overestimates the speed of change no awesomely warm and dry spell in the offing for this June I think. Longer term - will heights reestablish over Greenland again into July? I am struck again by the continuing depth of the cold SST anomaly off the US east coast and by the strength of the trades this month and slow passage of the pacific wave. However I reckon the start to July at least will be a good one for summer lovers as a long wave pattern more conducive to better weather takes hold.
  12. Yep. Signs at the very end of extended EPS modelling as pointed out by Northwestsnow that it may drift westwards a bit - but I wouldn't put lots of money on that. The pacific is certain to fire up at least a bit, and that will mean some kind of counter to dominant trades at the moment....but the waxing and waning of a long wave pattern is not the same as a pattern shift and that La Nina-esque smell to the pacific forcing during a weak El Nino phase seems to be a long term factor that continues to carry weight. My mind keeps being pulled back to the winter gone, when just about every expert and semi expert and NWP modelling felt that a pattern shift on the back of substantive increases in AAM was likely....but it never came. SSW impacts didn't quite align, and a stubborn +NAO phase was determined to remain in charge despite moments of definite challenge. We have now flipped to a very definite -NAO shape on the back of the final warming - and I wonder if we are once again going to see a setup through the summer where the established elements of the early season pattern are resistant to change.
  13. Greenland blocking showing no sign of relenting yet. I wonder if we have a residual long term impact of the stratospheric pattern through winter which kept suggesting blocking to the NW but didn't deliver until winter was gone...and now we have a semi permanent feature without a wintertime vortex to shift it. Whatever the cause - true summer heat for any length of time will be difficult to achieve for as long as pressure remains high over Greenland. Cold sea surface anomaly off US east coast also helping maintain reasonably active atlantic trough beneath the block, while unusually cold surface temps in the Med wont be helping with the establishment of a Euro high. Pacific trade winds also seem to be forecast to hold off progress of the pacific wave for another week at least, so any shift in the standing wave pattern looks on hold for now. End of June may be the next realistic opportunity for a change in pattern - 2 more weeks of low pressure dominated UK with occasional Azores ridging and generally average to below average temperatures possible. Keep an eye on Greenland...and if you are like me enjoy the continued lack of hayfever and excessive heat. Rain in the garden and reservoirs plus a bit of thunder in the air is no bad thing at all.
  14. Good post from Tamara as usual - always worth visualising the general shape of the standing pattern, currently sitting comfortably in a hemispheric 2 wave shape. As stated - expected progression of the MJO ought to see a decline in the mid atlantic ridge and lowish pressure over Europe to something more favourable for those who like their air warm by around week 3. The interesting extras at the moment are the persistence of blocking over Greenland (something we craved over Winter and didn't get...) and the very drab nature of the current Nino. I have no particular agenda to force here - summer for me is a period of waiting and hoping to minimise sweat and hay fever - but 2 thoughts. With Nino sitting between 0 and 1 and forecast to decline slightly it is not certain that an increase in AAM will be sufficient to provide the downstream alteration in the ridge/trough position dramatically enough to pull up anything particularly hot over the UK in the medium term. The other observation would be that if the Greeny High is here to stay, perhaps a residual of the winter vortex collapse, then the passage of atlantic systems may remain further south than sun worshippers crave, even if a Euro high gets established. Atlantic SSTs also seem to me to be supportive of an atlantic system track immediately to our west, a signal we may have been guilty of under reading 6 months ago. I wouldn't want to take a big punt on the summer to come but moving into the start of the season with a very neutral and unmoving ENSO signal plus blocking to the NW doest suggest anything remarkable in the next 4 weeks to me. Beyond that - anyone's guess. The winter gone showed starkly how long term signals and calculated hemispheric progression can be awry in both the minds of forecasters and supercomputers at even fairly short lead times. Might the currently cold sea temperatures in the Mediterranean also suggest less support for a heat carrying Euro High through the summer season given starting conditions? Musing always fun.
  15. Agree. Some anomaly images are already showing that we did indeed have a strong positive anomaly over Greenland. Unfortunately we also had one off to the WSW......and that meant no undercut by low heights. This is the starting point of my own investigation into what has happened when time allows. Forecast models got the high lat anomaly correct - but the strength of the sub tropical high deflected all the energy of the atlantic up and over the top...giving much more of a Nina feel to things than the expected Nino background. Why was the sub tropical AH so resilient? We have seen this often in recent years as you say here. Is this an effect of generally rising pressure in the christmas pudding where the ice cap is under extreme stress and the oceans warming? The itch I cant quite scratch in terms of that argument is that relative pressure patterns are what drives surface flow. Does a warming world mean the end of relative pressure variation? Obviously not.....so something else is at the heart of AH resilience and the inability of the NAO to turn negative. Masiello has tweeted this season that he thinks the run of +NAO years is at an end. i'm going to try and pick his brains a bit on that. Lots to follow up on!
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