Nick F

Worth reading this analysis from Isotherm on AmericanWx re: where it went wrong this winter. Although it is on an American weather forum, the points Tom makes are relevant for Europe aswell: https://www.americanwx.com/bb/topic/51698-my-winter-outlook-2018-19/?do=findComment&comment=5184369 From what I can glean from his analysis in respect of Europe, in a nutshell, easterly QBO at 50mb helped trigger the SSW, but descending westerly QBO at 30mb going into winter + weak El Nino was forcing an unfavourable northern hemisphere pattern with Nina-esque pattern of sub-tropical blocking and expanded Hadley cells rather than sub-tropical troughing typical of El Nino. So even though we saw the -AO in January following the SSW, the Azores sub-tropical high would not not be suppressed, so at best the NAO was neutral but mostly slightly positive, despite some height rises over Greenland at times, so we never really saw a decent -NAO to bring deep cold. The MJO was active, but amplified in the warmer phases because of more uplift/convection over the Indian Ocean (warmer phases) and subsidence over Pacific (colder phases). All in all, the Pacific forcing (ENSO/MJO) along with QBO structure and resultant SSW and +AAM in the wrong places all transpired to prevent high latitude blocking. Tom makes an interesting observation that the easterly QBO at 50mb and westerly QBO at 30mb has only occured twice since the late 70s, these two years Nina like in winter patterns. Caught many long range forecasters out, not because of poor forecasting but more a case of bad luck the way the QBO has transpired at different levels of the tropical stratopshere and it's impact on extra-tropical patterns but also background weak El Nino /neutral ENSO and lack of pattern response to the SSW. No only was winter poor for snow lovers in northern and western Europe but also for NE/E USA. The La Nina-esque pattern does favour western USA for cold and snow, as we've seen and still see Seattle, Las Vegas, large parts of Arizona and New Mexico buried in snow, even higher parts of LA seeing snow. Also Nina type patterns for Europe means most cold and snow is confined to NE/E/SE Europe. Hopefully winter 2019/20 sees more favourable pattern driving align, Solar minimum perhaps impacting too.

True, the Atlantic SSTs likely cooled off since Jan after the persistent cold Pm air crossing towards Europe into early Feb, but I would think with longer daylight and higher angle of sun there will be greater moderation of the moist long-fetch maritime flow come early March, a drier cold continental flow or drier arctic northerly wouldn't be affected so much by the longer days/sun aspect, as we saw in March 2018. But be interesting to see how cold a Pm flow will be in early March and whether it can produce much in the way of snow away from high ground, I would think more of struggle than earlier in winter.

Extended 00z EPS (days 10-15) suggest a general downward trend in T850s and heights from the west across western Europe, indicative of westerlies featuring increasingly prolonged and colder Polar maritime airmasses visiting the UK. However, Pm flows in early March IMO likely more marginal than we saw back in late January/early Feb - so wouldn't expect as much snow away from northern hills as we saw a few weeks back! But the trend, for now, is increasingly unsettled and cooler/colder westerlies pushing out high pressure as we start March.

Both GFS and ECMWF seemed to have backed off warmth for Saturday, which had been earmarked for peak of warmth, high pressure over Europe appears to be extending further west, so not such a strong southerly flow away from the far west, having said that, temperatures still in the mid-teens on Friday and Saturday afternoons, which is well above the seasonal average, but the 13th Feb 1998 record of 19.7C looks less under threat. Almost overlooked tomorrow afternoon, Netweather's SR model indicating 17-18C over north Aberdeenshire and Moray - likely from Foehn effect in the lee of Highlands/Cairngorms. EC has 15-16C in similar area of NE Scotland, also across Vale of York

Storm & Convective Forecast Issued 2018-08-06 21:33:50 Valid: 07/08/2018 00z to 08/08/2018 00z THUNDERSTORM OUTLOOK - TUESDAY 7TH AUGUST 2018 Synopsis North Atlantic upper trough will begin to amplify S and SE across the far west of Britain during Tuesday, with a strengthening upper flow across the UK – as SWly jet stream shifts S and E across the UK. Ahead of the jet streak, a weak surface cold front will progress slowly east, to lie North York Moors - West Sussex by 00z Weds. A very hot, humid and increasingly unstable airmass ahead of the cold front across SE England and East Anglia is forecast to destabilise and produce thunderstorms in the evening here before the front clears through and introduces cooler and more stable air. … SE ENGLAND and E ANGLIA … Surface-based CAPE will build up through the day due to surface heating of humid plume in conjunction with lapse rates steepening in association with advection north of EML (elevated mixed layer) aloft. However, this surface instability is likely to remain capped. However, a shortwave in the strengthening flow aloft will move NE from Bay of Biscay area in the morning crossing NW France in the afternoon. The increased lift by the shortwave along NW edge of hot and humid plume over France and SE UK combined with increasing mid-level instability as dry air intrusion punches NE overlapping plume, is forecast by many models to break out thunderstorms across Brittany and Normandy by early evening, before spreading / expanding NE across SE England then East Anglia through the evening. Thunderstorms are likely to be elevated, though 40-50 knots of 0-6km shear forecast will allow storm organisation into clusters, perhaps even an MCS passing over parts of Kent and eastern E Anglia, so there is potential for strong storms that may bring locally intense downpours leading to flash-flooding, isolated hail, strong wind gusts and frequent cloud-to-ground lightning. These storms should clear away NE into the North Sea after midnight. Issued by: Nick Finnis

Well written piece Quicksilver, lessons to be learnt for future winter forecasting, because despite how encouraging some signs, such as the SSW, and a few cycles through favourable 'colder' phases of the MJO, it appears there are other background drivers overriding these and muting their effects on upper patterns. Must admit I and others have probably overlooked the effects of the Atlantic SSTs and the tripole along with the PDO. My own take in a blog for Netweather below on how I thought it may have gone wrong this winter, a lot of it because the SSW displacement of the split vortices being unfavourable and also of the Pacific state driving upper patterns unfavourably, notably the +ve SOI which has lent to a more Nina-esque patterns through much of the winter, despite weak Nino / neutral ENSO, not to mention the wQBO going into this winter - which is often linked to stronger Atlantic jet / +NAO. https://www.netweather.tv/weather-forecasts/news/9403-winter-201819-sudden-stratospheric-warming---but-why-no-beast-from-the-east

We saw another Sudden Stratospheric Warming to begin the New Year, but why, unlike following the February SSW last year, has there been not Beast From The East? View the full blog here

Few less towels on the ring floor now perhaps, key is lifting that stubborn Euro block north, lag effects of MJO through 7-8 may help with that, also getting the northern arm of the split jet round the block to dig more SW on the eastern edge of the block to drag the deep cold our way and drop those heights over mainland Europe, increasing undercut from Atlantic side of the block may help too.

Back to the hunt for cold, seems to be a trend from the 00z/06z GEFS to drop heights across SW Europe as Atlantic troughing digs SE past the Azores as the jet splits over the Atlantic because of the ridging over Europe, with southern arm dropping SE into Morocco and northern arm going east across Iceland to Scandinavia, any deep cold kept well at bay by the northern arm though.

You have to bear in mind that it is not unusual for GFS underestimate maximum temperatures to the lee of high ground in the west, as the model vertical resolution may not pick up the air warming to the lee of mountains as air dries out and descends (i.e. the Foehn effect) - limitations of the grid points the model uses to show temperatures may not pick up local quirks and variations in temperatures caused by the foehn effect, simply because it doesn't use enough grid points. The higher resolution 00z ECM is showing, at noon Friday, 14-15 C across NE Wales/NW Cheshire plain to the north of the Snowdonia mountains, also pockets of mid-teens across Devon and west Wales in lee of high ground. Can't post the paywall chart unfortunately.

Extended 00z EPS ensemble mean shows quite a strong -ve height anomaly / trough over Azores, especially days 11-12, while downstream stronger ridging building N and NW across the NE Atlantic. However, suggests a fine line between mild southerlies and a cold continental flow, depending on where surface high pressure sets up - which the mean will blend out the different options.

Yes, the NAO has been stubbornly positive through most the winter, despite the favourable signals, such as the SSW and MJO, to suggest it may change -ve, It was positive even when we had a period of -AO since the new year - that was probably connected to the SSW. The lack of troughing between Azores and SW Europe and ridging over Iceland this winter and the last several winters for the most part testament of predominantly +NAO pattern which seems to scupper any prolonged cold spells. If a full blown El Niño developed, rather than weak to neutral ENSO, we may have seen more in the way of -ve episodes at the back end of this winter, but with neutral ENSO and +ve SOI we are seeing more of Nina pattern. The below tweet re-iterates the dearth of -NAO episodes in recent winters: I guess many forecasters were pinning hopes on a fully fledged El Niño running the show through the winter, when in fact it’s been very weak or neutral, BOM hasn’t declared El Niño conditions so far. In fact we have seen more of a La Niña atmospheric state for much of the winter, certainly recently. This I think because the Southern Oscillation Index SOI has been positive in tandem with neutral ENSO- which has manifested in more of Nina conditions. However, this may not be the full answer and there are a lot of unknowns to why this winter has panned out as poorly as it has for prolonged cold and lingering snow despite a major SSW and a few cycles through colder MJO phases. Obviously something has been interfering between the usual tropical convection - high latitude interactions and also strat-trop coupling following the SSW, but have yet to see any affirmative answers. Guess for many it’s a continual learning process in the school of weather!

Thanks, I've been guilty on a number of occasions this winter of getting carried away and jumping on the SSW and/or MJO going through 'colder' phases being a definite force for good and WILL change the patterns without addressing the caveats too. Some do of course attach the caveats of caution to the possible benefits of the 'positive' signals, something I will certainly do from now on, after those positive signals have clearly not manifested in the troposphere (such as SSW) or have been overridden by other factors (MJO). Worth pointing out the drivers and teleconnections are still a useful tool, but being too confident in their use to predict more than 10 days ahead can easily end up with too many bust forecasts. This winter has been a good test for those longer range predictions. Onwards and upwards, still plenty of time for the pattern to change to bring one or two more last hurrahs of cold and snow, but I suspect in similar vein of the winter so far they may be brief and marginal affairs. Noticed posts discussing the solar minimum, yes we are reaching it, but we could bottom out this year and into early 2020 before activity curve rises back up. Cold winters can occur when the activity has started to rise out from the min, 2010/11 winter was on the rise from solar minimum, so potential we could still get two cold winters a row.

Has become rather tiring following the models now for me, it is quite clear that despite the SSW and MJO cycling through favourable colder phases a few times over the last few months contrarily there has been no pattern change to trigger HLB and this looks to remain the case for the next few weeks. There has been episodes this winter where big atmospheric drivers, which can force pattern changes for the better, such as MJO, SOI and of course the SSW to start the year have been forecast by models several times to manifest favourably to have impacts on the upper patterns that would normally promote high latitude blocking that would at least turn the NAO negative and increase our chances of seeing deep cold and less marginal snow events. However, in case of the MJO, we've seen head through 7-8 back in early January, before heading into COD, but no high latitude blocking to show for it for the rest of the month, we've seen since the start of the month the MJO slowly move out of 6 into 7 only to stall and head back into 6. This stalling is not really not going to help promote enough poleward amplification other than north across Europe. The model forecast do suggest, at varying speeds, the MJO heading back through 7 and on through 8, GFS slower but more amplified than the quicker ECMWF. But, the models predictions haven't been great with the MJO this winter, with the reality of the stalling and slow progression of the MJO back and forth in 6 or 7 this month so far probably why we are seeing the Euro height rises but not any hints of HLB down the line. Since Dec 31 2018 Forecasts from GEFS and EC There could be various reasons why the MJO impacts on the upper patterns of the mid-to-high latitudes of the N is rather muted, there has been some discussion on twittersphere and American forums that the SSW at the start of the year and the way it had developed and manifested has hindered the usual positive impacts of the MJO going into 'colder' HLB promoting phases. But also the neutral ENSO has also played a role. We are currently seeing a more La Nina-esque look to the upper flow patterns over N America and N Atlantic (with -PNA and +NAO), the SOI (Southern Oscillation Index) is normally negative during El Nino and positive during La Nina - and low and behold it has mostly been in positive (Nina) territory this winter so far, with just brief recent dip to neutral barely negative and now on the rise again. This has been in tandem with a +NAO too. El Nino usually better for promoting HLB in conjunction with MJO colder phases, the progression of MJO into 8-1 as forecast models should go hand in hand with a -SOI, but I am sceptical whether we get out of 7 quickly as ECWMF suggest. So we could see more of the same flat pattern of low heights to the north and Euro heights for next few weeks. So with the above in mind, it really exposes the limitations of using MJO forecasts and stratosphere forecasts along with AAM/GWO predictions to predict very far ahead, beyond 10-15 days at least, with any confidence. As this winter has shown, there's just too many conflicting signals. The tropical oscillations, stratosphere state along with AAM/GWO are still valid predictive tools, but must be used with caution. Many professional meteorologists both in the UK and USA use them to predict a few weeks to a month ahead, but have busted by predicting cold wintry weather and instead its warmed up .Some more daringly do a forecast all three winter months using longer-term predictors such as ENSO forecasts combined with QBO and longer range NWP forecasts such as CFS, EC46, JMA, GLoSEA, etc. But equally there have been some big busts on winter forecasts. So, where does that leave us for the rest of the winter? Well, I have low confidence atm of any change that will bring HLB. There is still a possibility IF the MJO can get a move on through 8-1, yes the models show it atm, but we are still stuck in 6/7 with no real impetus to move for now. I would earmark the final few days and beginning of March for a pattern change that may promote HLB, if the MJO wave impacts the upper patterns with out interference from other drivers, but there is also no guarantee that the HLB will develop in a favourable position either. Could end up to far west to our NW for example. We have 3 weeks left of February and most of March to still get some snow, but it looks like the next few weeks would be hard pushed to see any for most. It will take a pretty brutal deep cold blast to bring ice days and lying snow for long in March too and early March 2018 or March 2013 are unlikely to come every year, so worth lowering expectations in that regards.

Well, the model ensemble guidance has been chopping and changing as much as the operationals over the last week, just when it starts to look promising in the hunt for cold, a new signal develops in the starting data which takes model guidance on a route away from the promising signs - been the story of the winter really, despite background drivers suggesting hope. Our last chance hope for the remainder of meteorological winter is the MJO wave passing through phases 7-1 at decent amplitude - which normally forces changes in the upper patterns to promote blocking at higher latitudes - with a lag of 10-14 days - we may not see this potential until the closing days of February. In the meantime, a last hurrah of wintriness on Sunday, as low drops down from the north with colder air cutting in behind perhaps giving a wintry mix, as suggested by ECMWF Sunday night for England and Wales Then I'm afraid it's back to late December / early January pattern of high pressure dominating - fairly mild sunny days and chilly nights under clear skies until we see the pattern shaken up by something, probably the MJO.

Just a quick one from me, seems to be a theme developing today from GFS/GEFS and EC/EPS (so far) to by pass a Scandi high developing and instead ridge builds north over Western Europe next week, before perhaps building NW to Iceland/Greenland the following week. The reason, tropospheric polar vortex other side of Svalbard extending SW into Scandi, then perhaps eventually further SW over Europe from mid month with a ridge west or NW of UK by then. Going to be a slow process to get there and may have to endure a little mildness on the way, but I think the easterly may be off the table for now and besides it probably wouldn’t have brought us deep cold anyway given forecast temps out east next week.

Yep, good sets of clusters which support for a Scandi block thereafter then retrograde of the block, Atlantic troughing making inroads to the SW of UK too.

Again 18z GFS takes an eternity to build high pressure to where we want it, with UK under WAA while the ridge builds N close to the east, before it gives up and the high sinks on a brighter note, new EC weeklies looking positive anomaly wise, with where we’d expect the +ve anomalies to be given MJO progression, below weeks 1-4, but the weeklies have looked promising all winter!

Today's GFS RMM plot gone a bit berserk with the MJO amplitude through phase 8, but the 12z GFS operational running with MJO P6-8 in February reanalysis composite script of heights building N over UK (phase 6), then Scandi ridge building (phase 7) then retrogression of ridge toward Greenland (phase 8 ) The GFS was suggesting zonal winds in the upper stratosphere pushing down and coupling with troposphere later this month, but that seems to have disappeared on today's NAM plot with the easterly winds still dripping down through the troposphere after 20/02. So perhaps we have not seen the back of the SSW reversal impacting the troposphere and indeed it may continue to impact on tropospheric circulations for a while in conjunction with the MJO colder phase wave amplification and retrogression. Some similarities since beginning of the year to perhaps Jan/Feb 2013 following the SSW in early Jan that year, in 2013 there were bouts of cold, though not prolonged, with some milder episodes, it took 2 months for the full effects of the SSW to impact Europe with deep cold from the east - which resulted in an historically cold March. Cold may come sooner this time, but perhaps not on the severity of March 2018 or March 2013.

06z GFS seems to be a lot slower building the ridge N and NE next week compared to ECMWF, but then the model does faff around getting out of phase 6 then slow through phase 7 compared to EC too on the RMM plots, so maybe why it takes an eternity to get the high over Scandi. The slower the ridge building north the more likely it is that it doesn't build where we want it as the TPV has more time to strengthen then flattern out the flow.

If the ridge can retogress toward Iceland 2nd half of month as per forecast MJO progress implies, and it's a BIG if, then we could perhaps open up the Siberian or arctic floodgates .. but we need to see whether the TPV co-operates too.

We can still get a cold and blocked pattern with a -PNA, would certainly mean less temp contrast along NE North America to fire up the jet stream with all the cold over western N America.

Still a fairly decent signal from ensemble z500 means for Scandi high day 10, though EPS mean signal stronger than GEFS. Taking 00z GEFS z500 mean into the extended and we can see the Scandi height anomaly retogressing towards Griceland area: This fits in with the standardised MJO composite progression from phase 6 through to phase 8, with height rises over UK (P6) then Scandi high (P7) then Greenland/Iceland high (P8) - MJO progress such as we are seeing advertised by the model RMM plots, GFS most amplified with this, but generally seems to have a better handle on MJO phase 6-8 With the SSW impact perhaps waning, we may perhaps see less interference with the MJO impact on poleward wave driving However, the ENSO base state does have an impact on the kind of pattern response to MJO cycle. Recent ENSO update from NOAA CPC suggests ENSO neutral rather than El Nino: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf ENSO neutral with MJO phase 7 and 8 brings this in the composite: P7 P8 ENSO El Nino this with P7 and 8 P7P8 ... so the models certainly lurching more towards a neutral ENSO MJO 7-8 response. However, the patterns often never play out exactly to the composites and this has been a strange year with regards to muted pattern response to the MJO cycles through 'colder' phases, likely to do with the SSW interference and there's no guarantee that the SSW may not still be impacting the pattern in next few weeks. So we'll see!

I guess we are finishing the day on a more upbeat mood with regards to our fortunes around mid-month compared to the recent prospect of zonality as far out as the models went, 12z GEFS and EPS mean supports the idea of the 12z EC operational for height rises over Scandanavia & disrupting Atlantic trough by mid month, whether a surface high over Scandi can build far enough west to bring cold easterly remains to be seen, 18z GFS smelling the coffee, but more runs needed to see if this may be a more fruitful chase than just another close but no cigar chase. 12z EPS suggests potential for slider lows again in the means even if we don't get a full blown easterly. Whatever the outcome in detail, certainly a move away from mobile Atlantic low pressure dominated pattern to one dominated by high pressure from mid-month, the NOAA CPC prognostic charts back this up