Model discussion highlights

[MattH]

17 hours ago, Tamara said:

You have provided a very good example of something I have repeatedly made on the few occasions I visit this thread. The MJO is just one part (an important part) of the whole atmospheric circulation wind-flow budget. The relationship and interaction of forcing in the tropics has to include the extra tropical circulation as determined by the Global Wind Oscillation (GWO) which is a plot depiction of aggregate wind-flow in both tropics and extra tropics.

Providing an accurate diagnostic analysis using these particular weather tools continues to be hampered by the diagnostic maproom of the Global Synoptic Dynamical Model (GSDM) being out of operation since the middle of March. Despite indications that this would be fixed, nothing as yet has materialised in respect of resolving the problem.

In the absence of this highly useful and insightful information & data, comparison of VP200 tropical convection anomalies, convergence zones within these anomalies, trade wind strength and fluxing of wind-flows between tropics and extra tropics can't be be compared as usefully against the ongoing strength of atmospheric angular momentum (AAM)

Westerly Wind Bursts (WWB) continue  across a wide swathe west of the dateline

 

However, in respect of the tropics it is complex presently with this extensive area of attempted eastward push of westerly inertia across both the  Maritimes and the Western Pacific and with some (relative) weakness of inertia from the dateline and into the eastern Pacific. Such "west based" forcing is influencing the extra tropics in a way that is a-typical of many El Nino transitions, especially with -ve PDO forcing persisting.

Angular momentum is above average in accordance with the direction of travel of increased propagation between the tropics and extra tropics, though is is not possible to see both frictional and mountain torque budgets which would confirm the precise locations and strengths of wind-flow propagation into the extra tropics.

C/o the -ve PDO and extensive forcing across a wide swathe west of the dateline then the total angular momentum anomaly does not have a breakdown analysis of the aggregate forcing and therefore not tell the whole story as much of this extra tropical propagation from the tropics is blindsided by this -ve PDO and residual 3 year La Nina lag. Hence the present stronger pressure anomaly of the Azores High (which in previous posts was predicted to play less of a role this coming summer).

I think this continues to be the case. The forcing west of the dateline is very strong with a lot of warm water upwelling trying to push eastwards across the dateline. Summer wavelengths heading into June, a waning of the a-typical ENSO forcing in the coming weeks, and the tropical standing wave becoming greater focussed across the Pacific itself (and less around 120E to 150E) are likely to evolve the advertised pattern towards less Azores ridging across the Atlantic and  troughs cut-off west and south west of mainland Europe bumping up against downstream high pressure zones across much of northern Europe.

This could be a summer of thundery/thermal low being advected northwards and north eastwards and repeated plume type heat - rather than stationary prolonged dry heat conditions.

The coming week down here across Portugal and Spain sees the first hints of that change which should become more influential with time as they embed across continental Europe as downstream high pressure ridges establish themselves fairly close to the N and NE of the UK

 

Hi @Tamara.

Just an FYI, but I was 'speaking' with David (Gold) yesterday and he confirmed it is a big problem, linked to IP routing issues which he is trying to sort out. However, he also followed this up by stating that it "probably won't come back unless we completely rebuild on a new cloud account", while "Victor (Gensini) has been working for a long time on a new setup, with some input from me and Klaus, but we wanted to run both side by side for a long time to compare"

Essentially, whatever happened IT-wise doesn't look like it'll get resolved soon and, for now at least, the GSDM page is dead in the water, which is clearly a sad loss for those with an interest. One can only hope that Victor comes up with another layout and platform because I get the feeling that given the new cloud account issue, David won't get his back up and running now and will wait for Victor to set his new layout, or whatever it is, up instead.

As for the forecast and outlook, the current and upcoming more anticyclonic spell has been well advertised and discussed for some time and is certainly a good example of the usefulness of the GSDM, when used in the correct way. NWP was flopping around a week or two back, while the long-term prediction was steadfast as May progressed. This signal was picked up on back in mid-April as part of internal discussions and forecasts for work, quick screen grab of a section of a doc highlights well, out of interest...

Looking ahead and your commentary about a potential troughed pattern to the W and SW of the British Isles is what the majority of the seasonal models predict for June, these were recently reviewed, again, for work, from the Copernicus website. It'll be an interesting summer to keep tabs on this year as the focus will clearly be on whether another 40C heatwave can occur again, especially seeing most, if not all data continue to suggest that Continental Western Europe will see significant +ve temperature anomalies once again. The combination of the El Nino and the -PDO is clearly a conflict, while the eQBO may have some say, seasonal models also do suggest that any blocking could be at a higher latitude than what many may want to see. I certainly don't see this summer being a 2018 repeat, for example, and still fully expect it to be a far more typically British one, characterised by the usual mixture and frenzy of a week or two of heat, humidity and thunderstorms, but then likely cooler, cyclonic refreshment from off the Atlantic, but, as ever, time will tell.

Cheers, Matt.

 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4855735

[Cambrian]

The hemispheric ribbon of mid-latitude heights is slowly making a full loop around the remnant tPV and then tightening it as the summer proper approaches. 

Day 3 and day 10 ensemble mean anomaly charts from the 0z ECM neatly show the trend for next week, the low Mediterranean heights are a bit of a sideshow for us for now as the core Atlantic heights maintain their extension through the UK and Ireland. 

 

Any longwave polar troughs are shallow if existent at all, the waning very clear between days 3 and 10 here on the 0z ECM mean

 

and op,

 

as even the elongation from Iceland to northern Japan recedes, getting cut off to the east by the rise in heights pushing east through Siberia. 

As a result, there isn’t a hemispheric wave pattern to speak of. With this NH setup, it might soon become very difficult to see where the next batch of meaningful rain is going to come from. 

It’s not until week 4 (12-19 June) that we get a combination of near normal heights (weeks 3-4 shown below)

 

and a slight low pressure anomaly (weeks 1-4) on yesterday’s updated ECM weekly mean anomalies.

   

A potential thundery interlude, but as reflected earlier in the week, this has to be taken with a pinch of salt, as it keeps getting pushed back. All in all, a very dry outlook indeed for the more reliably foreseeable. 

Regarding temperatures, the question might just be at what point with long days, nearby high pressure and strong sunshine that a northeasterly becomes warm, as that is the consistent wind direction on the weekly mean anomalies for the next 6 weeks! Just how near the high we get is probably the answer. 

Week 2, as we head into June, looks like warming up a tad, as the centre of the high sets up nearby for a while,

 

before getting pegged back a bit in week 3 as the high moves back west and the northeasterly flow strengthens once more. 

 

Maybe a bit cooler near north and east facing coasts at times then, but on the whole looking to be very pleasant for a good few weeks. A very respectable start to the summer. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4856143

[Cambrian]

Gin clear sky here today and the 0z ECM has provided yet another good run. Most likely completely dry for the vast majority for the next 10 days.  The day 10 mean and its anomaly keeps the solid form of recent days, a very generous apron of positive heights encircling a very hemmed in and much diminished tPV. 

 

Temperatures on the mean pushing high teens to low twenties inland and slowly rising heading into June. Here are the ensemble runs temperature and precipitation composites for Birmingham and St. Helier, much less diurnal range by the sea.

 

Clearly something in the continued modelling of lower heights and pressure to the south, with the Jersey pressure mean consistently a few millibars lower than Brum, although 1017/1018 mb compared to 1020mb at day 15 isn’t indicative of any decisive breakdown yet.

 

More precipitation spikes appearing as we head into June granted, but interestingly, more of these inland further north than down in the channel perhaps suggesting reliance for these ensemble members on convection to deliver the rain rather than more organised frontal precipitation from cyclonic development. Overall, the spikes are clearly in a minority of ensemble members in any case. 

Even out to day 15, the ECM mean showing pressure around 1020mb for the UK and Ireland, 1015mb further south over the southern half of France - so at this stage, more of a distant brush on the snare drum than rocking the shop. Notwithstanding our awareness that the models can change quickly, this is the clearly established core pattern of the models at the moment. 

 

The ECM control run is often worth a look for a less averaged out indication of the strongest single “feel” of the model for the overall direction - here at day 15, low pressure still bubbling away over the Med but with a 1025-1030mb high for the UK and Ireland, same gentle anticyclonic northeasterly flow as we’re getting used to seeing, not getting too hot too quickly but steadily getting warmer. A very pleasant outlook for the foreseeable future. Good times. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4856497

[Cambrian]

This is an analysis of the extension of the duration of the blocking signal on the ECM extended range weather regimes forecasts since 24 April. 

The first line on the graph (in blue) shows the total number of days with a blocking signal on each forecast, which are denoted by the little hatched rectangles near the bottom of each forecast chart. This shows the growing trend towards a blocked pattern over the last 8 forecasts. Thursday’s forecast achieved the maximum 46 days, every day with a blocked signal, but there had been a steady build towards this full house. From the graph, the model flipped to the correct solution with the 1 May forecast and has been firming up on it since then. 18/05 chart; my graph.

 

When the signal first appeared on 1 May forecast, it was for a period of blocking to begin around 8 May, which was then brought forward a day to 7 May on 4 May forecast. So taking 7 May as the start date of the blocked spell, the second line (in green) shows the total number of days since 7 May with either a blocking regime observed or forecast, so the last point on the graph, for instance, is the result of adding all the days since and including 7 May (blocking observed) plus all those running through to 2 July (blocking forecast), which is 55, close to the maximum possible of 57, but subtracted 2 for a couple of days since 7 May that have turned out in the event to display no regime attribution (grey in the chart below). 

For looking at the current performance of the extended range forecasts, the most complete verification available is from the chart from 6 April (the observed regime is shown in the row of rectangles running right along the bottom of the chart beneath the hatched rectangles showing the forecast). 

Though it makes the correct regime designation on only 18 out of 43 days, the 6 April forecast picked out the beginning of the blocked period more than a month before it transpired, and does seem to be very good at picking out the broad transitions. One other point - if anything, when the forecasts haven’t performed so well, it’s mostly because the extent of blocking observed has been underestimated in the forecast.

Another six weeks of blocked weather? All through June? Personally, I doubt it, simply because that’s a very long way to go at any time of the year without something working in off the Atlantic. It will be interesting to see if tomorrow’s regime forecast merely adds on another 4 days to the end of the wall-to-wall  blocking signal or gives the NAO+ signal a bit more of a look-in during June. 

Even if it does continue to signal blocking, it’s also becoming clear that with the consistently below normal heights over southern Europe tending to work their way north, a blocking signal over the Atlantic-Europe zone only relates to the lack of west to east movement, and doesn’t mean that it will be dry and settled over Europe, far from it.

In that way, on this occasion if the change when it does eventually come is due to encroachment into the UK and Ireland of these lower heights from the south, we may be less likely than usual to pick up advance notice of an imminent change in our weather from these regime forecasts. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4856897

[Kirkcaldy Weather]

 

On 04/05/2023 at 17:48, Kirkcaldy Weather said:

"Does appear to be a trend in the West Pacific being the main zone of interest for the MJO even heading to the extended range"

About 3 weeks on from that and we are at that point of MJO activity across the Pacific 

 

Matching to the composites with phase 5>7 for May+June 

We can see the evolution of the Atlantic high which is currently the main driver of the UK weather this begins to transition to an Atlantic trough with possibilities for the high to reposition further east which with favourable alignment might setup the first plume opportunity within 3-4 weeks 

On 04/05/2023 at 17:48, Kirkcaldy Weather said:

with other similarities to 2015 I see that being a good benchmark so I'm thinking warm conditions and storms 🌩🌩 plume style setups. Some of the monthly models have been hinting at wetter conditions near & across the UK which increases my thinking of the above.

I especially like this composite for accuracy of the recent setup, Note the trough over Italy which I'll discuss in a sec 

 

 

CFS in agreement pretty much and beginning signs for the Atlantic trough and high further east

Incredible that the low that started across the UK evolved into a stagnant trough parked over Italy delivering record rain amounts and sadly Fatal flooding

 

We also did have heavy snow in Iceland with blizzard warnings on 15th May

'I'd say we could have high pressure records and/or high temperature records broken across the Pacific Northwest and Alaska / Canada'

Amazingly the smoke from the wildfires (especially in Alberta) are being moved across the Atlantic and over the UK

 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4857439

[Tamara]

The broad scale pattern of anomalous high pressure locating close to the UK with lower pressure across southern Europe is well advertised by the numerical models and as previously discussed in respect of the non numerical diagnostic model.

The further outlook may create some erratic modelling  as a (temporary) drop in AAM occurs as the present tropical convection concludes and re-sets across the Indian Ocean. However with the low frequency tropical convection standing wave pressing the west/central Pacific and surpluses of westerly inertia feeding from the tropics into the extra tropics, then caution is required as to the longevity of an blocking breakdown indicaton and cool air advection c/o high pressure relocating NW/wards On this basis better not to read too much into the significance of retrogression in the longer term (for UK and NW Europe) as such a pattern does not look sustainable (if it occurs) heading though the greater part of June. Most likely leading to a re-set of an Atlantic trough and a downstream ridge to the east. An eastward adjustment of the pattern to come over the next week which implies very warm plume like conditions.

The lower heights now established across the Iberian peninsula leading to some very unsettled conditions with floods in SE Spain and some quite large thunderstorms elsewhere and across the border into Portugal. A couple of thundery showers here in my own locality yesterday.   A supercell (c/o Portuguese social media) pictured across the Capanca coast (due south of Lisbon) was pictured yesterday which produced some sizeable hail. Some flooding in Lisbon itself.

 

 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4857730

[Tamara]

3 hours ago, MattStoke said:

I’m remembering Tamara’s advice to be cautious of any NWP showing retrogression.

There is sometimes a problem when a change is hinted at in numerical models towards the end of a 10 day period and it then tends to then get extrapolated out in time as some kind of sustained switch in pattern. Taking these evolutions as snapshots in time and set against the general direction of travel of the atmospheric circulation presents some context and perspective.

As mentioned yesterday, computer modelling will jump on the signal from the conclusion of the present ENSO "mini cycle" which acts to provide a (temporary) buffer to the highly anomalous westerly inertia within the tropics and extra tropics as both negative trending frictional and mountain torques serve to bump up the trade winds and the vacuum needs to be filled c/o decelerating the downstream pattern accordingly (retrogression)

But this is just a natural lull period in the overall trend away from La Nina type influences and renewed westerly winds added back into the system should re-set the pattern heading through June. This next re-set is especially interesting in respect of the fact that summer wavelengths will assist the placement of the anticyclonic wave breaking further east and that implies greater influences from southerly and south easterly vectors. At the same time, shallow low pressure anomalies from Iberia and Biscay become more influential and provide some thundery incursion interest accordingly.

So attempting context of the suggested cooler incursion is always a good thing.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4858031

[Cambrian]

Yesterday’s ECM extended range weather regimes forecast captures the retrogression of the high beautifully, with a strong Atlantic ridge signal for the first 11 days of June replacing the general blocking signal of Monday’s  and previous forecasts. 

Retrogressing highs seem to receive a mixed reception on here, but with the strength and duration of the sun at this time of the year, a cooler air mass is just as welcome for me. Lovely fresh mornings and good long days you can work with. And starting June with a  blocked Atlantic is always a heck of a lot better than a procession of low pressures heading our way out of Newfoundland. Monday / Thursday forecasts.

 

Besides the firming up on the retrogression, the weekly mean heights and pressure anomalies comfortingly remain with the same broad theme as recent weeks. By week 3,  lower heights and pressure slowly encroaching from the south. The weak Scandinavian trough of the end of week 1 into week 2 is short-lived, the lower heights merging with those to our south, the orientation looking a bit more interesting for a potentially more lively spell around mid-month with more of a pushing up of low heights from the southwest by week 3, the gap in positive heights directly to our north inviting more of an incursion. Weeks 1-4 mean heights anomalies. 

   

Probably noticeably warmer and more humid for a while before more of a chance of a change to something a bit more concertedly changeable, particularly further south. Weekly pressure anomalies, they get wishy-washy after week 3.

  

This corresponds to a period following the Atlantic ridging with no overall signal on the regimes forecast, still all very slow moving, so there could be a good few days of wetter weather around mid month, as low pressure features, thundery maybe, slowly work their way in from the south, and if they do, they might well stick around for a while. The heights soon return to our north the following week, with what looks like a good setup for a southeasterly. 

This is out to week 3 / 4 with all the obvious caveats, bells and whistles, and in the meantime in the more reliable, an extended period of very pleasant early summer weather to enjoy. Then maybe a few days of rain to freshen things up mid month before a resumption of more summery conditions towards the end of June, but very likely a good deal warmer than the beginning of the month. Sparkling again here, have a great day.  

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4858305

[Downburst]

Seems to me that there is a very clear signal, despite what day 10 may show on any particular run for northern blocking to persist to the end of the month. This is shown on the ECM weeklies, and we will know more later when Thursdays output is released. But in essence there's a reversal happening right now and it is very clear, Iceland is the new Azores and Azores is the new Iceland possibly to the end of the last third of June. It's not until July that there is indication of troughing in the west Atlantic of the weeklies. I have to speculate is the record breaking sea temp anomaly in the southern half of the north Atlantic playing a part, it will take time for that to phase out. I don't know of course.

Speaking of day 10, ECM shows this clearly with what the ECM call an Atlantic Regime and the weeklies suggesting this moving east over time to a blocking pattern. Great news for food production in Iberia and for Scotland and Northern Ireland and Northern England all round. 

Edit to say I had not seen Cambrians excellent post above, to which I am entirely in agreement. Top class. He should do the Met Offices 10 day outlook.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4858306

[Cambrian]

Another beautiful day here. A very good spell through to Wednesday on the 0z ECM op, a delightful end to spring as core heights just to our southwest build in to a good looking cell of high pressure with the central heights over the UK and Ireland, here at day 4, the weak northerly arm of the jet stream preventing the high from moving north. A notable southern arm too, providing an Azores low and propping our high up from the south, holding it in the Goldilocks zone. Increasingly warm for most with light winds. Always an easterly flow in the south which might take the edge off the growing warmth. 

  

A fascinating outlook thereafter for the UK and Ireland, hinging on the extent to which our high pressure retrogresses and the precise direction in which it migrates. Paradoxically, it floating off towards Greenland in itself isn’t necessarily curtains for our good spell, like here at day 7, heading into next weekend, despite the low heights over northern Scandinavia, we maintain good heights, both arms of the jet stream ebbing at that point. 

  

It’s during the early part of the following week when that southern arm reinvigorates through the Canaries, with a better formed Azores low and the prospect of a more direct merging of the low heights with the base of the Scandinavian trough rather than having to go the long way around Italy, that weakens the heights over the UK and Ireland and nudges the high more notably west into the mid Atlantic, allowing heights to fall away straight to our north. 

  

That’s the full regression there at day 10, that first opens the gates to the north and maybe something cooler and showery, before the southern arm might really start playing with our heads later in week 2, if and when it edges further north, like the extended range forecasts have been suggesting. 

One end of the spectrum in the current models is that we get a full retrogression that allows the trough to move west over us for a while like here at day 12 on the 0z ECM control, with a bit of an “ouch” northerly and a cyclonic influence,

 

while the other brings up the low from the south to Cape Finisterre like here at day 12 on the 0z GEM control, warmer and drier for a while but a good possibility of some thundery rain pushing up from the south in time. 

 

Southern arm similar on the two, it’s the weaker northern arm that’s the vagary. While it’s the southern arm that is looking to drive the retrogression, it’s the position and state of the weaker northern arm and the extent of southward trough development that it supports that will determine our weather. It’s all far too far out and far too marginal at this stage for a meaningful punt.

And far too much time spent looking at these charts, I’m off to enjoy some of the glorious impacts that they on occasion depict. Have a good one.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4858627

[Tamara]

3 hours ago, Mike Poole said:

Well, it’s bank holiday Monday - and today’s the day, if you recall the models a week ago, that the GFS (with some support from the ensemble suites) had us in a cold northerly, due to this retrogression.  It hasn’t happened, and has kept being pushed back, in fact on this morning’s GFS 0z, the retrogression signal has been pushed back to beyond T270.  Here’s T270 and T330:

Neither the GEM nor ECM show signs of it in their 10 day range either.  Looks like a phantom retrogression to me! 

The modelling of the sub tropical jet stream continues to be of personal interest. From a southern European point if view in respect of the monsoon that has set in across the Iberian peninsula, but also how it plays its part in locking in the high pressure belt across more Northern parts of Europe (very much including UK)

Late Spring thoughts, as expressed over the last week/10 days keep consolidating on an early summer pattern evolving into low height anomalies increasingly established across the Azores (and eventually edging towards Biscay & SW approaches) & downstream ridging locating more and more to the north and east of UK/NW Europe and a tendency for higher humidity and convection trying to encroach from France into southern and western UK 

This time last year deep blue skies and scorching heat were established and set to dominate a dustbowl drought summer down here. This year is very different - seeing towering cumulus each day and strong thunderstorms especially across the interior parts and skies like this pictured yesterday (across northern municipalities of Portugal on this occasion)

 

The further outlook suggests that sub tropical jet stream is set to become more and more influential and I think for weather watchers also further north across Europe there could be some good photo captures to be taken as this instability bumps up across the entrenched downstream anticyclonic zone.

Happy UK B/H.  There are two Portuguese holidays in the coming week.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4859361

[Cambrian]

I can honestly declare that my awkwardly overheard comment to the effect that it’s all looking a bit wobbly this morning, which gained a poor reception locally here, was actually aimed at our incumbent high pressure.

The ECM extended range weather regimes chart from yesterday picks up on this nicely, the Atlantic ridge signal for 2 June, corresponding to a moving west of the core heights in the Atlantic to the southwest of Iceland here on the 0z GFS mean anomaly, before being edged out by a renewed blocking signal by 5 June, fitting in with it wobbling back east and extending heights further east over southern Scandinavia and down through Central Europe. 

   

By day 10 (above right) it wobbles west again (no use of the R-word in this post!), withdrawing the heights from Central Europe and refreshing the strong Atlantic ridge signal, but still looking good for the UK and Ireland. 

As alluded to above - great to see your post, @minus10, it looks like there is gaining momentum for a change around the middle of June, with a loss of both the ridging and blocking signals and a modest uptick in the NAO+ signal. The 0z GFS mean is picking up on this too, at the end of the 0z run, with lower heights edging up from the south, reflected too in the ECM weekly mean anomaly charts for week 3, 12-19 June, for heights and pressure. 

  

Looking to be less settled for just a few days at the moment though with the blocking signal returning strongly by the summer solstice. 

The weather here this morning is absolutely lovely again - not the slightest bit wobbly actually. Strangely brighter indoors too. I must stop talking out loud as I write. Have a great day. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4859606

[MattH]

3 hours ago, Mike Poole said:

That is currently the suggestions from the models in the post-10 day range.  However, given their recent performance in overblowing this scenario, given the thoughts on here of @Tamara  and @MattH, and given what the seasonal models were predicting for June last month, you would have to question the marked part of the regimes plot from the ECM 46:

Is this a phantom signal again, would be my question? 

The Atlantic ridge signal could be related to the expected spike in the PNA pattern looking ahead, which is set to become quite significant, this all links in with an Aluetian low pattern, W USA Ridge, E USA trough and downstream of that an Atlantic ridge, this links into the period when the UK may well then see more of a trough pattern as we approach the mid-June period. Clearly, there is still some evidence for a -ve NAO as well. To what extent any troughed pattern becomes established is the key uncertainty and for how long, but the evidence is clearly stacked now towards another significant rise in AAM, from a "low" point of approx +0.5sd currently, we are already seeing a jet extension pattern modelled as well (see below GEFS example). This is highlighted well by the overnight EC46 and how the trend is, in particular, as June progresses, while the VP200 anom pattern is also indicative of a Pacific that will see further -ve VP200 anomalies, without any active MJO event.

In terms of the next significant MJO event, then the consistent signal here is for a likely event through the end of June and into early July, not before. We can see this consistently within the CFSv2 plot (highlighted by the solid red lines) and also the ever-useful and reliable EWP plot as well. It will be very interesting to keep tabs on this event as it would be arriving during the mid-summer period and could well have some significant 'say' as to how the patterns evolve through July and also August as well. From what I envisage, it could push the UK into a very warm or hot summer pattern during the second half of July, but all are very open for discussion at that time frame.

Also as has been discussed for some time, the current anticyclonic signal was discovered back in mid-April, the recent fall in AAM and +ve PNA trend does support a pattern where the current NW European high ends up more to the W or NW, with a troughed pattern over the British Isles, leading to a more convective interval, but not a 'full blown' cyclonic period, and with then support for another AAM spike as June progresses, allowing for a reset of the pattern, but with the risk that unlike currently, the main CoG of the high is more over or to the east of the British Isles, with a trough to the W or SW. Could that then become the primary default pattern for much of the summer period (?) time will tell, as I do think there is still scope as well for northern blocking at times this summer, not necessarily just a European high, but one long-term event that will need watching is the amplitude and influence of this MJO event that should arrive later June and into July.

Cheers, Matt.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4859726

[Cambrian]

Yes, there’s clearly a high degree of marginality too in what the regimes’ algorithm designates as an Atlantic ridge or a blocking signal. Comparing with the previous forecast from last Thursday, it’s modified a 3-day chunk from the middle of the 11-day stretch indicated in the last forecast for the start of June, in favour of a quick little peak in the blocking signal. Thursday / Monday 

 

I’m guessing that the algorithm is essentially working off the difference in heights between the Atlantic and European zones. In this setup, it seems to be very dependent on how far into Central Europe the peripheral heights extend from the Atlantic, and very sensitive to changes of just a couple of hundred miles at the southeastern edge. 

It clearly is primarily an Atlantic high, albeit oscillating, in the first instance, supported by the bolstered Atlantic ridge signal over the next few days, during 1-3 June, 0z EPS day 4, though with the surface high extending southeastwards beneath the core heights to take in Ireland and the UK. And it’s an extensive block, peripheral heights stretching from Newfoundland to Austria. The 0z ECM mean anomaly animation for the next 10 days neatly shows the wobbling of the core heights of the high west to east then west again. 

  

To be fair to the question as to whether it actually does move back that far west in reality despite the cross-model agreement (GEM mean onboard now too (day 10 mean anomaly above) along with GFS means posted earlier) it is fair to point out that this continues to ghost us as a day 10 signal more reserved to the means. Added to this, heights through Central Europe have proven more resilient than forecast at week 2 time and time again, so I share the reservations. The 6z GFS op migrates the high to Scandinavia, with a meaty looking upper trough having dug out the Atlantic high as early as day 8.

 

The loss of ridge / blocking signals from around 8 June and the subsequent drift to no overall signal consistently being shown on the regimes does suggest that the heights do eventually relax enough to allow some lower heights and shallow low pressure to influence particularly Western Europe, but this is a slow change, the 6z GFS op eventually having done the deal by day 12 with low pressure for UK and Ireland, and until then at least, it looks like we continue what is becoming a notably dry spell.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4859683

[Cambrian]

Irrespective of the position of the high and its proximity to the UK and Ireland as it wobbles around from run to run, it’s slowly having the life squeezed out of it anyway. 

The heights are leaking away by day 8, here on the 0z GFS mean and their anomalies, and the central pressure falls by 10mb to 1025mb, so it’s no longer a strong high in terms of heights or central pressure by the second week of June. 

 

Similar on the ECM mean through to day 10. 

 

The 0z GFS ensemble mean (Birmingham) shows a steady falling away in pressure, 12mb or so over the next 8 or 9 days. The ECM shows similar.

 

There is a return of a good number of precipitation spikes in the second week too, indeed a big contrast between week 1 and 2 on both the GFS and ECM. 

 
Their scatter in terms of heaviness and over time perhaps suggesting a leaning towards convective rainfall, rather than anything that organised.

Temperatures look to remain pleasant and we keep those healthy diurnal ranges, which as pressure slowly falls and instability increases, will help feed the showers and the development of local features.

 

l’m being a bit brave I know, but though it will take time, and the timing itself is going to be up for grabs, the direction of travel looks to becoming clearer, the steadiness and consistency of the modelled fall in heights and pressure starting from today is what persuades me to feel that there are now good indications that the block is on the wane and that we’re likely slowly drifting towards a change in the weather - to a setup with much more scope for some rain, probably at some point in the second week of June. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4860128

[Cambrian]

The last month has been a memorable spell for how very slow moving the pattern has been and how we have so often been under the influence of high pressure. A feature has been the gentleness of the wind, I cannot remember a year where the blossom on the fruit trees has remained so completely undisturbed. It might be a very good fruit yield this year which would be most timely. 

The 12z operational runs for day 10 from the big three are are actually very similar in signalling an end to the high pressure regime. Low pressure systems on all three over the Azores and Norwegian Sea, a bit of a race on between cold and warm air masses in their pincer movement around the eastern flank of the Atlantic high as it weakens and withdraws west. ECM / GFS / GEM. 

  

One of those times where whether by hook or by crook, we’re going to get a change. And it might be quite a dramatic change if we get the pressure low enough and a bubble of warm air from the south wins out like on the 0z GEM at day 10, temperatures in the twenties widely, mid  twenties in the south, just as that frontal system starts to push in from the southwest. 

  

That could get very interesting (in our very typical “couple of days of properly warm weather then it all goes boom” kind of way!). A lot of people would probably welcome that, some more widespread warmth, for those in eastern parts too, followed by some welcome spells of rain, with warm sunshine in between. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4860479

[Cambrian]

0z GEM operational run really going for it - a few days of building heat from a week today heading into the second weekend of June, mid to high twenties widely, up to around 28 degrees in many parts of the south and east by the Saturday, as the low anchored to the west of Portugal draws a plume of warm air up through Western Europe. 

    

Once we lose the nagging northerly component around the high, some reasonable uppers and the strength of the June sun does the rest!

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4860598

[Cambrian]

Telling set of mean anomaly charts from the 12z GFS. 

At day 7, still very similar to what we have become very used to seeing. Good heights close by to the northwest of the UK and Ireland, southern running jet stream still a long way south, supporting that low over the Azores and the other one over the eastern United States. A pocket of lower heights running from Greenland through to Finland. The zero anomaly line running into the very north of Spain. 

 

A week later, day 14, the Azores low is averaged out, but the zero anomaly line has encroached to the north of France. Above average heights still through the north of the UK. And take a look at that, running north from there, up through Iceland and Greenland to cover the whole of the Arctic. 

So some higher potential (but still very much only a possibility) later in week 2 for convective episodes edging in with the building warmth from the south is pretty much the most we can expect in terms of rainfall from a very static Northern Hemisphere profile, with close to zero west-east mobility, that even moving forward from mid-month is looking docile in the extreme. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4860949

[Cambrian]

The ECM weather regimes forecast update from yesterday is holding firm with the combined Atlantic ridge / blocking signal for the next couple of weeks, adding to our suspicions that the subtle changes expected around  mid month are being put back a bit, with the signal now lasting until the 18th / 19th. 

When it does eventually wane, it’s interesting that a degree of a blocking signal is maintained but it is (partly) replaced by a NAO- signal as well as a slightly more modest NAO+ signal, so we’re dropping a combination of high pressure signals for a combination of signals that together suggest that some parts of Europe will have an easterly flow and some parts a westerly flow, which together with the maintenance of a degree of blocking, suggests shallow low pressure centred somewhere along the boundary of the Atlantic and Europe.

The weekly mean pressure anomalies for 5-12, 12-19, 19-26 June are in keeping with this admittedly retro-fitted idea, continuing to show the slow advance of a low pressure anomaly over the UK and Ireland and much of Europe, suggesting a slow change to less settled conditions. 

  

The weekly mean heights anomaly charts show the Atlantic heights continuing their arduously indecisive retrogression, allowing lower heights to steadily move up from the southwest over parts of the UK and Ireland by week 3…

  

…with some warmer air working in…

  

…to potentially give us around a week or so of more mixed weather, with no surprise if it turns out to be a quite thundery spell, before solid blocking is signalled to return by the end of the month. Have a great day. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4861089

[Metwatch]

This morning's ECM up to 10 days away.

Spot the blocking high pressure.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4861264

[Cambrian]

Some of the data and imagery we have at our disposal these days and the speed of delivery is truly outstanding.

These are from the 6z ICON op showing the diurnal flux in humidity and  temperature over the next three days, hour by hour. They show the nightly invasion of higher humidities (and by inference, low cloud) from the east coasts of England, Scotland and Ireland, and the burning back each day, with the consequent impact on daytime temperatures, though the nights remain cool everywhere. 

 

It’s been an unkindly lengthy period of cool, and at times dull weather further east. Western parts have had a real taste of early summer, and continue to do so over the next few days.  Anyone fancying some warmth this weekend, then head west. Not often able to say that - usually very much the other way around!

However, it’s good to see the cooling influence and moisture of the northeasterly flow quite considerably reduced for all early next week, the tide of warmer shades extending further east as temperatures begin to pick up more widely. 

Again great to look at, the 6z GFS op temperatures every 6 hours out to day 10, a switch back to the usual, with it cooler out west, heating up considerably at times in central and eastern parts.

 

Then a new type of chart for me - the convective cloud and precipitation, shows the increasing scope for thundery weather from next weekend onwards. Have a great weekend everyone. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4861512

[Cambrian]

While the models might have overplayed the extent of the regression in some of the more dramatic runs in the 12-14 day range, a modest regression has definitely occurred and this has essentially been modelled very well. 

Here are the 0h ECM anomaly charts from the 0z runs for the last three Saturday mornings - 20th, 27th, 3rd. There was a westward extension of more positive heights from just to the west of Ireland to the Atlantic south of Greenland between the 20th and the 27th, though the core heights remained to the west of Ireland; followed by a migration of those core heights northwest between the 27th and today, with a part withdrawal of the heights from northwest Europe. 

  

It’s been slow in nature, but modelled well in the 10-day and 7-day range. Here are the ECM mean anomaly chart for day 10 from 10 days ago, and the one for day 7 from 7 days ago, compared with today’s chart for today.  The chart from 7 days ago is naturally a bit better, particularly for the trough development, than the one at 10 days, but for both, just as modelled, the core heights have moved west, peripheral heights withdrawing from Central and Eastern Europe and the south of France, helping the development of the Scandinavian trough as modelled. The model also picked out the further build in heights in the Hudson Bay area. The marginal discrepancy is between core heights just to the southwest of Iceland as opposed to just to the south of Iceland. 

  

For the notoriously difficult task of modelling the relatively rare pattern of a retrogression, it’s really not a bad effort at all !

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4861692

[Tamara]

On 06/05/2023 at 13:29, Tamara said:

Forthcoming strong WWB's will re-set the developing and rapidly strengthening Nino influence in the Pacific and this has very interesting implications heading towards and into June and the start of summer.

Heights in the Atlantic and an ebbing and flowing Azores High are not likely to be the default this summer as they have been in recent summers. Low pressure encroachment to the west and downstream ridges (with thundery potential breakdown to re-set rinse and repeat) look more probable with only temporary interruptions to this pattern when ridging in the Atlantic is evident.

Olá, boa tarde. Um sábado feliz para todos

Numerical models now seeing past the red herring of retrogression based on adjusting their expectations for the floor of angular momentum to be higher than believed in the last ten days of May.

This allows the evolution suggested in the copied post back in early May to become increasingly advertised with those implications for some proper summer warmth and ultimately quite a change for those in the UK close to the chilly North Sea cloud and breeze - as the steering vectors finally switch much more to the continental landmass of mainland Europe.

The thundery unstable pattern across Portugal and Spain for the past 10 days also tending to migrate slowly NE'wards with time. A catalyst for this will be low heights across the Azores this coming week expanding towards Biscay and the SW approaches in the further outlook.

Westerly inertia is set to keep re-booting through the tropics and propagating into the extra tropics through this summer. Therefore a subtle split jet stream accordingly allowing a sub tropical arm of the jet to sustain low pressure to the west and south west in the Atlantic - underpinning continental and Scandinavian high pressure ridges, This could be a summer with something for everyone. With that in mind and it being  exactly two years to this date since arriving permanently in Portugal  -  hopefully a summer ahead that the early season rains down here will have helped prevent the severe water shortages of last summer. 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4861594

[Mike Poole]

ECM clusters this morning, and the envelope of uncertainty is continuing to shrink in the T192-T240 period:

The centre of the high remains to our north on all clusters, but is east of the UK on the first, close to the UK on the second and to the west on the third.  So it is drifting around run to run, but even cluster 3 is not that big retrogression signal that the models had previously and have now dropped.  T264:

What is becoming notable in this timeframe, as shown by clusters 1 and 2 today, is convergence towards the anomaly shown in the seasonal models for June.  This is probably best shown by the anomaly shown by the ECM seasonal model.

As June progresses, we will need to watch the low anomaly to the SW, the extent to which it encourages southeasterly winds and warmth to the UK, and the potential for thunderstorms if it encroaches into the UK.

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4861935

[Cambrian]

A fascinating tussle over the next week between lower pressure and heights slowly nudging northeast from the Azores and stubborn heights over the UK and Ireland and eventually to our northeast here on the 0z ECM mean and anomaly. 

Day 2 

 

versus day 7.

 

While the heights remain stubborn, there’s a drop of around 12mb in surface barometric pressure by next weekend, lower pressure that should support greater vertical instability, in a period during which the air mass warms up considerably - the T850 is 7 degrees above average by next weekend, here on the ensemble mean, so greater energy inputs too. 

 

The models will struggle to pinpoint precisely where and when it might all bubble up into some heavy rain and thunderstorms, but the increasing potential by next weekend is further supported by the change in the precipitable water vapour - the amount of water vapour in the atmosphere, taken from the 0z ECM op. 

 

This introduction of a combination of lower surface pressure, some genuine warmth in the air mass and the rising humidity could well lay the foundation to some dramatic weather by next weekend. Have a great day 

Original post: https://community.netweather.tv/topic/98519-model-output-discussion-15th-march-onwards/?do=findComment&comment=4861965