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In depth (chilled out!) model discussion


Paul

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20 hours ago, Singularity said:

In fact more than that; a clear 'bubble' of higher heights across Greenland by 1st which may have some support from the stratosphere as a ridge is also evident up at 30 hPa for example. Or perhaps the ridge works up from the troposphere?

It's the latter.

18 hours ago, stodge said:

I see two issues and I wonder if these happened during other spells of predominantly snow free winters in the UK: - first, the warmings seem to come disproportionately from the Siberian side and that has the initial response of throwing the PV back to NE Canada/Greenland. We would need a significant Canadian warming to displace the PV to Siberia.

Second, even when vortex displacement occurs, it isn't a "clean" lift leaving enough residual energy over Canada/Greenland to help the LP factory going and prevent the formation of HLB.

So the process is warming leading to vortex consolidation over NE Canada/Greenland leading to a messy secondary displacement to Siberia leading to a new warming sending the energy back to Canada/Greenland and the cycle repeats and the best the British Isles can hope for is either a brief N'ly regime or a Scandinavian HP which inevitably sinks as the PV displaces back to Siberia and the northern arm fires up.

Later in the winter/spring the PV is weaker and there is more opportunity for it to be further displaced west into Canada giving Greenland HLB a chance so a cold March is always more likely than a cold December on that basis. Exceptional winters (which this hasn't been) need a break in the cycle either via a Canadian warming or a clean displacement to Siberia.

Not sure I follow your reasoning. The warmings in the temperature charts show up on the Siberian side but this is the norm - the predominant forcing is planetary wave 1 which more often than not gives stratospheric anticyclone on Pacific/American side pushing vortex to Eurasia/Atlantic side. On these occasions (i.e wave 1), warming will usually coincide with the eastern edge of the vortex and then progress along the northern edge, with the coldest temperatures from the centre to the western flank. The warming in the temperature charts over Asia doesn't show that the strat vortex is pushed to NE Canada/Greenland - though as the forcing varies with height giving a baroclinic vortex with the centre rotated westwards it isn't unusual for, say, the upper levels eg at 1mb to be located there, 10mb north of Scandinavia and 100mb over Siberia for example. But then the location of warming at each level also moves westwards accordingly. How this is then reflected in tropospheric low pressure systems over Canada/Greenland is not directly or linearly related.

In a nutshell, usually wherever the strongest warming occurs at a particular pressure level, the vortex is adjacent to it.

Edited by Interitus
clarification
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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

Cheers Interitus - so I gather we're looking at a lagged phase 8 MJO response that builds upward and reinstates a displacement of the stratospheric vortex toward Asia?

Also I see what you mean about the vortex and warming events - and this is where the sense that displacements aren't good for cold weather in the UK come from; they are mostly as a result of Asian-sourced warming that occurs because the tropospheric/lower stratospheric vortex is over Canada/Greenland, where we don't want it to be.

Exceptions may well exist if the vortex is far west enough, so more toward central/western Canada.

For the elusive Canadian warming, it seems an unusual configuration of the mid-upper vortex is needed. Late autumn was particularly unusual last year and we came close to a technical CW. I believe we came within a gnat's whisker of a December to Remember, only for unexpected tropical activity in the Indian Ocean to kick off a feedback that trashed the whole configuration for us. It will be many decades before that defeat from the jaws of victory no longer triggers a furrowing of my brow. Same goes for the equally horrific failure of the models to correctly handle the MJO-related signals for mid-Feb this year. 'twas the winter of our greatest discontent! Well, mine anyway :wallbash:

 

Never mind, moving on...

- - - - - - -

Cross-posting from the MOD thread as permitted;

It's been a long time since we last had a jet stream shifted south yet remaining quite strong and sending lows across the UK. With a few tweaks and occurring in the depths of winter it can be a snow-lover's nirvana - but on this occasion, due to the time of year plus quite possibly the overall warmer state of the climate, this will only ring true for up on the mountains in the north, and even there perhaps only intermittently.

ALL_emean_phase_full.gif  MarchPhase2gt1500mb.gifgfsgwo_1.pngMarchPhase3gt1500mb.gif

We have a fairly strong bit of MJO activity in the IO at the moment, in terms of wind signals - convection is lacking. The odd run here and there has toyed with moving the ridge from our N to our NE seemingly by way of response, but it seems to me that with signs of the GWO nosing into phase 4, the models are finding too much of a subtropical ridge + flat westerly signal to let this really take shape. Whether that 'too much' is down to model judgement remains to be seen - I've often seen an MJO signal rise up to seize the day having initially been underestimated... but that was back before the winter of 2016-17 which if anything has displayed the reverse tendency, catching a fair few forecasters/climatologists out - including me of course; the MJO enthusiast.

Still - I believe the blocking high to our N should start to be able to exert a more direct influence in the 8-16 day range, though from what location exactly is hard to say. If the models keep trending toward MJO phase 3 to follow phase 2 then a failure of the blocking to move to our E/NE could mean that it sticks around to our N for a long time. Increasingly I worry that with GWO orbiting negative - albeit weakly - the jet might keep on firing across under such blocking to bring about an exceptionally unsettled and wet March. We could really do with the hints of El Nino in the Pacific forcing a bit of a kick in GLAAM to hold up the Atlantic lows. Hopefully a Kelvin wave will turn up to help things along.

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Posted
  • Location: East Ham, London
  • Location: East Ham, London
On 2/25/2017 at 08:01, Interitus said:

Not sure I follow your reasoning. The warmings in the temperature charts show up on the Siberian side but this is the norm - the predominant forcing is planetary wave 1 which more often than not gives stratospheric anticyclone on Pacific/American side pushing vortex to Eurasia/Atlantic side. On these occasions (i.e wave 1), warming will usually coincide with the eastern edge of the vortex and then progress along the northern edge, with the coldest temperatures from the centre to the western flank. The warming in the temperature charts over Asia doesn't show that the strat vortex is pushed to NE Canada/Greenland - though as the forcing varies with height giving a baroclinic vortex with the centre rotated westwards it isn't unusual for, say, the upper levels eg at 1mb to be located there, 10mb north of Scandinavia and 100mb over Siberia for example. But then the location of warming at each level also moves westwards accordingly. How this is then reflected in tropospheric low pressure systems over Canada/Greenland is not directly or linearly related.

In a nutshell, usually wherever the strongest warming occurs at a particular pressure level, the vortex is adjacent to it.

I'm not a professional forecaster - just a muddled amateur. What I think you're saying is that wave 1 warmings probably won't do the UK much good in terms of changing the tropospheric pattern so we need the mysterious (well, to me) wave 2 I often hear mentioned.

The fact remains I see a "response" to each wave 1 which seems to be to re-consolidate the vortex over NE Canada/Greenland but why is the vortex there ? Why doesn't the PV settle over the Bering Strait as an example ? If you're telling me it's because that's how the planet works, fine. It also seems that what I see on a 10 HPA chart might not be reflective of what's happening at other levels of the stratosphere. I was interested in the March 2013 profile because even though it was a very cold spell for western Europe, it took place with a strong cold stratosphere still in existence and the positioning of the coldest areas looked to be being repeated this year.

I still have much to understand it would seem.

 

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

A rare opportunity to have a Sunday peruse of the charts but a shortened version of my usual methinks.

GEM 00Z at T+240, Wednesday March 8th:

gem-0-240.png?00

Not much sign of an immediate pattern change it would seem. Indeed, signs of the jet returning north as pressure builds from the south. Heights over Greenland but of no influence at this point it would seem.

ECM 00Z at the same time:

ECM1-240.GIF?26-12

A very different profile over Scandinavia with a hint of rising heights we often see on this ECM chart but the Atlantic looks to be in charge albeit perhaps slowing,

GFS 00Z OP at the same time:

gfs-0-240.png

Again, we see a slowing Atlantic and pressure rises from both north and south. The NH view of the same chart is enlightening with a significantly displaced PV:

gfsnh-0-240.png

However, in furthest FI, a strong Aleutian ridge builds sending the PV back over our side of the globe but possibly toward Scandinavia or NW Russia.

gfsnh-0-384.png

Have to say my hopes of a significant pattern change from a Greenland HP appear to be waning although the GEFS still have plenty of options and plenty of cold options on the table at T+240.

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Posted
  • Location: Surrey and SW France.
  • Location: Surrey and SW France.
10 hours ago, stodge said:

I was interested in the March 2013 profile because even though it was a very cold spell for western Europe, it took place with a strong cold stratosphere still in existence and the positioning of the coldest areas looked to be being repeated this year.

Hi Stodge.

The 30mb stratosphere was very different to now in 2013 - after the major SSW in January, the vortex was split asunder and never regained its former strength.

SSW split                psnh_pen_hist_z30_201303.gif

This time in 2013 psnh_pen_hist_z30_201310.gif

This is what it looks like currently - ie displacement where it is a game of push and shove but no destructive force.

                               psnh_pen_hist_z30_201710.gif

I find it easier to look at animations to see how the season develops - the link I'm using allows you to do this as well as using the drop down menu to change picture. The fact that you have levels for strat, Z500 and surface, allows you to see whether it is upward wave action or downward propagation.

http://ds.data.jma.go.jp/gmd/tcc/tcc/products/clisys/figures/db_hist_pen_tcc.html

An edit to add the GFS 12Z 30mb run in animation format.

http://brunnur.vedur.is/kort/gsm025/2017/02/26/12/gsm025_nhem_gh30_t30.html

The 30mb level is well represented at the 500mb level and if it continues to be so - one could expect a more dipole outlook with the possibility of ridging in the Atlantic and a trough in our vicinity. Amplification is the name of the game but it is where this actually sets up as to whether our narrow corridor of longitude sees mild or something unseasonably cool.

The JMA wants to stick quite rigidly along lines of MJO P2 for second week of March but that is contra indications from the strat!

Y201702.D2212.pngMarchPhase2gt1500mb.gif

  

Edited by Nouska
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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

First, thanks to Nouska for updating my knowledge of the stratosphere which is all part of being on here. The stratosphere seems to be a complex multi-layered beast open to interpretation and misinterpretation it would seem. The 10HPA profile from March 2013 told another story but as seems to be clear, we need to split the vortex rather than displace it. I presume no one knows if there was a vortex split in winters as 1946-47 and 1962-63 or whether that was more about displacement.

Back to the here and now and after a very wet night in London, let's see where life's great meteorological journey is going to be taking us next month (perhaps):

We are at Day 13 of what I thought would be a 21-day minimum spell of Atlantic-dominated weather following the breakdown of the February cold spell and the subsequent major warming.

Looking ahead to what would then be Day 23 (as it were) - Thursday March 9th:

Starting with GEM 00Z OP:

gem-0-240.png?00

The theme throughout the GEM output is mobile with a push of heights from the south which doesn't succeed and heights over Greenland which serve only to keep the LPs on a more direct west-east track. It's looking like a wet start to March and snow to higher elevations can't be ruled out at times.

ECM 00Z at the same time:

ECM1-240.GIF?27-12

Some subtle differences and signs perhaps of the jet swinging back north but the Atlantic isn't exactly firing on all cylinders and a view of the same chart from the NH perspective tells a different story:

ECH1-240.GIF?27-12

Strong heights over the Pole and more than a hint of those coming toward us. The evolution from there might be of interest.

GFS 00Z OP at the same time:

gfs-0-240.png

GFS has hinted at height rises from the south over its last few outputs so it's to be taken seriously. The trough is digging south into the Atlantic and a more amplified picture generally suggesting (to me) further FI could look quite spring like.

gfs-0-384.png

Well, it gets there in the end, sort of, but it's a bit of a struggle.

Looking at the NH view of those last two charts:

gfsnh-0-240.png

gfsnh-0-384.png

The core of the PV has shifted more to Siberia but there's enough residual energy at the far end of FI to prevent height rises over Greenland but a weak Atlantic and weaker jet allows for the Azores HP to make its move and build toward the UK. Note the big HP over Hudson's Bay.

At this stage I'd say the picture moving into March isn't clear. The form horse might be for height rises from the south and that is suggested especially by GFS but all models show a weakening Atlantic and the possibility of height rises to the north certainly hasn't disappeared. My honest view at this stage is that a gentle move into spring looks more likely than a final cold flourish but that's far from settled.

Looking at the GEFS, though, there are some colder solutions in the mix at T+240 and certainly further out the idea of northern blocking is far from dead.

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On 2/26/2017 at 09:35, stodge said:

What I think you're saying is that wave 1 warmings probably won't do the UK much good in terms of changing the tropospheric pattern so we need the mysterious (well, to me) wave 2 I often hear mentioned.

The fact remains I see a "response" to each wave 1 which seems to be to re-consolidate the vortex over NE Canada/Greenland but why is the vortex there ?

No, both wave 1+2 warmings or displacements/splits as they typically refer to can produce colder conditions for the UK, or they can produce warmer conditions, or indeed little change at all!

As to wave-1 re-consolidating vortex over NE Canada/Greenland, this might be observed but is it any different from having no warming at all? The lagged composite response is actually for height rises in that area, but as with UK conditions, it varies between each event. Here is a good opportunity to link to the SSW compendium where the effects of individual SSW can be examined in more detail - https://www.esrl.noaa.gov/csd/groups/csd8/sswcompendium/

It is a little disappointing that they don't include charts for a shorter time range after the SSW eg. 0-14 days - quick response effects are often seen, perhaps inked to wave reflection by the critical line created by the zonal wind reversal for example, which fades away as the wind returns westerly in the 0-30 or 0-45 day timescales which have been chosen for anomaly propagation.

1 hour ago, stodge said:

I presume no one knows if there was a vortex split in winters as 1946-47 and 1962-63 or whether that was more about displacement.

Don't know about 1946/7, but there was an SSW at the end of Jan 63 which was classed as a split, and it is a good example of the points made above regarding the UK effects.

It was a bit of a slow burner which shows how tricky it can be to get the central date right for comparison with other events or creating composites. From the ERA40 reanalysis it was 28/1/63, from JRA-55 30/1/63. The NCEP/NCAR reanalysis chart below from 29/1/63 shows that it only nipped the end off the vortex leaving it mostly intact, more like a large wave break -

19630129.thumb.gif.f49821c1bfab23d4c0cd40724495c8b3.gif

And a few days later it looks like the cut-off daughter vortex rejoined -

19630203.thumb.gif.26cf8ab062adc84f408089e3fd0963e9.gif

Not very impressive and looks like recovering in the next couple of days. However, an analysis of minimum NAM by Martineau instead of day of wind reversal gives a central date of 11/2/63 at which time it looked like this -

19630211.thumb.gif.782b2452b9fdd251769ba7aece5b56b1.gif

That's a bit more like it! Though soon after it reformed to become more like a displacement again - the distinction between these is not always clear and a displacement can often feature a split and vice versa.

But here is the thing, whichever date chosen, the CET afterwards was still very low initially, but not quite as cold as before the SSW -

58b40aaf8ae24_1963anom.thumb.gif.c07c9109ae073d30bd187455b624b19e.gif

More interestingly, from some early composites I made from an assortment of 54 other SSW/minor warmings/final warmings, the 7-day running mean temperature trends after 11/02/63 match the composite CET anomaly response very well -

1963.thumb.gif.4f73daae69ccde1fa7f4d4301fe84953.gif

(Note the 1963 values are 7day running mean of CET seen in the previous graph, but then scaled for comparison).

So the SSW might been partially responsible for ending this legendary cold spell.

Here is the original post from 2013 - https://www.netweather.tv/forum/topic/74587-stratosphere-temperature-watch-20122013/?page=92#comment-2605326

 

Edited by Interitus
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Posted
  • Location: Surrey and SW France.
  • Location: Surrey and SW France.
11 hours ago, stodge said:

I presume no one knows if there was a vortex split in winters as 1946-47 and 1962-63 or whether that was more about displacement.

One can never be sure how accurate the extrapolated reanalysis is, on charts from the pre satellite era, but there is an archive that goes back to 1851 (20CRV2)

https://www.esrl.noaa.gov/psd/cgi-bin/data/composites/plot20thc.day.v2.pl

This would suggest there was indeed a split vortex at 10mb - prior to the onset of the severe winter spell in 1947.

Geopotential heights anomaly at 10mb - 5th to 10th January 1947 - from NOAA ESRL reanalysis.

878776da981ed6f4f20353ba89446e28.gif

The '62 - '63 winter is included in the JMA reanalysis link I gave in my previous post.

November kicked off with a Canadian warming (a displacement of the vortex off the Pole but not necessary for winds to reverse) - then SSW at the end of January.

psnh_pen_hist_z30_196269.gif   psnh_pen_hist_z30_196306.gif

Edited by Nouska
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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Thank you, my friend.

Plenty for me to consider and look through and a chance to improve my knowledge which is never a bad thing.

The "Canadian Warming" scenario is one I've heard mention though they seem as rare as hen's teeth in all honesty. Unlike 2010 when the bulk of the cold conditions occurred in the first half of winter, 1946-47 was a late starter (around Jan 22 if memory serves until early March) but 1962-63 started just before Christmas 1962 and continued for most of January before easing in February.

Can we then postulate that the Canadian Warming of late 1962 caused the split and/or displacement from which the tropospheric response was to set up the blocking HP scenario which kept Western Europe very cold but the SSW which triggered a displacement, broke that and ended the cold spell ?

In the absence of any data, we could postulate a Canadian Warming in late 1946/early 1947 and the end of the spell coming as a result of either an SSW or an early final warming ?

As Inheritus said, it seems we flirted with a Canadian Warming in November last year which, had other factors not intervened, could have led us to a very wintry year end and start to 2017.

Off to do some research...

 

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all

A gorgeous morning in deepest London and two weeks after the end of the last cold spell, it's nice to see some crisp chill late winter sunshine.

As we move technically into spring, what does the future portend (as it were):

Starting this morning with the model output for March 10th and I'll open the batting with GEM OP:

gem-0-240.png?00

A gentle northerly to end the output with pressure rising from the west but not as a link to heights to the north thanks to a couple of shallow shortwave features. Note the LP near the Azores.

ECM 00Z at the same time:

ECM1-240.GIF?28-12

A very different evolution - ECM was keen to send the jet back north yesterday and has continued in that vein with the trough aligned SW-NE between heights to Greenland and the Azores. A slack gradient to the east of the British Isles.

GFS 00Z OP at the same time:

gfs-0-240.png

Again, something a little different but keeping the jet going back north allowing pressure to rise from the SW. An early taste of spring on that chart especially for the south.

It's all very anticyclonic - a theme of this winter it seems and at the end of FI:

gfs-0-384.png

A lobe of HP from Greenland sits over the British Isles so fine days and cool nights would be the theme. Note the PV has plunged into the Baltic States.

T+240 on the 06Z OP:

gfs-0-240.png?6

From there, the PV seems somehow to come back to Greenland.

Fortunately for fans of cold the 06Z GEFS at T+240 have a number of cold options with Greenland HP a significant minority so in a sense very little has changed since yesterday even if the OP runs are not so promising:

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

All in all, the route to a colder evolution at the end of next week remains tenuously open but the form house seems to be the jet lifting back north at this time. We need the Atlantic to slow down to encourage HLB as there is a clear window of opportunity with the vortex being shunted further west.

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

Pinch, punch, first of the month and if we are to be believed, it's spring and everyone goes from wanting feet of snow and ice days to wanting warm sunshine and azure blue skies. Mother Nature doesn't care and March doesn't usually sing the right tune but let's see where we are this morning:

The output of Saturday March 11th starting with GEM 00Z OP:

gem-0-240.png?00

One of the big trends of recent days has been the signal to raise heights from the south as the jet shifts back north. GEM is quite anticyclonic and a hint of height rises in Scandinavia is replaced by the Azores HP shifting north. Plenty of energy to the north though and no sign of Greenland heights.

ECM 00Z at the same time:

ECM1-240.GIF?01-12

A fairly non descript mobile Atlantic pattern with LPs passing SW-NE well to the north of the British Isles. Some returning PM air in the mix and I'd imagine we'd be looking at typical March fare of sunshine and some potent showers offering transient snow to altitude.

Onto GFS and the 00Z OP at the same time:

gfs-0-240.png

Not a million miles away from either GEM or ECM at this stage - a chilly NW'ly flow but with pressure rising from the SW ahead of a temporary ridge and the next frontal rain. Not much changes out to the end of the run with the NH view showing low heights over the Arctic and the PV over the Pole.

Here's the 06Z OP at T+234 so the same time:

gfs-0-234.png?6

A rather more potent LP passing east to the north of Scotland so a strong NW'ly flow with gales or severe gales and some squally wintry showers. The NH profile at the end of the 06Z couldn't be more different to the 00Z:

gfsnh-0-384.png?6

Back to the 00Z and the GEFS are fascinating with a clear cluster angling for the Greenland HP block and this is reflected in the spread:

gens-22-1-240.png

To sum up, we haven't moved too far again today. The option of a Greenland based block remains firmly on the table even though the OP runs are looking more to a height rise from the south.

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Afternoon all :)

Another late runner for the day's update but it's a glorious day here in London with temperature at 11c so very decent for early March.

How are we looking moving into mid month or just before:

Starting with GEM 00Z OP at T+240, Sunday March 12th:

gem-0-240.png?00

A chart to please any cold weather fan in all honesty and it doesn't need much explanation.

ECM 00Z OP at the same time:

ECM1-240.GIF?02-12

Not in the same place but perhaps not that far away. The LP coming off the CONUS could swing North and allow heights to rise in mid Atlantic or it might not. Otherwise, it's a benign chart with a WSW'ly flow covering most of the British Isles.

On then to GFS and the 00Z OP at the same time:

gfs-0-240.png

Very different with a strong active North Atlantic jet firing LP systems toward the British Isles. Further into FI, the outlook remains very mobile but with PM or returning PM air becoming more dominant, the accent is on cool/cold conditions with rain/showers (snow to altitude).

The 06Z OP at T+234:

gfs-0-234.png?6

Something quite different. Yes, it's a mobile pattern but weaker with heights rising in Greenland and note the PV lobe dropping into NW Russia. The onward evolution is more curious - lower heights over Europe and an HP building from the west over to Scandinavia leaving the British Isles in a weak, cool E'ly with rain/showers especially for southern counties.

The 06Z GEFS tells the story:

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

The story is there are plenty of options ranging from very mild/warm through average to cool/cold on the table along with settled conditions or unsettled conditions. Those members building either a Greenland block or a mid-Atlantic block tend (not surprisingly) to be the coldest while those that don't tend to keep the milder Atlantic flow in charge. The other key element is the PV - the colder options lift the PV from NE Canada/Greenland while the milder members don't - again, no surprise.

My view on the output is the colder scenario for mid March has taken a step forward again today with very encouraging GEM and GFS 06Z output but the GFS 00Z was strongly Atlantic biased and the ECM, as it has been for some days, has been neither fish nor fowl and perhaps more indicative of model uncertainty than anything else.

 

 

 

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

So to Friday and well into the new month and let's see if the wintry interest of yesterday has continued with the overnight output.

Starting with GEM and with T+240 taking us to Monday March 13th:

gem-0-240.png?00 

GEM models quite an unsettled spell through next week leading to a brief N'ly at the end of next week. It is however brief and by Monday pressure is rising from the SW in a classic "toppler" situation whereas yesterday the ridge was angled north toward Greenland, today it's a more classic NE ridge though it has to be said no sign of a raging Atlantic behind it.

ECM at the same time:

ECM1-240.GIF?03-12

ECM has watered everything down this morning - the midweek warm up for the south is weaker as is the N'ly next weekend and we end up here with HP in charge and fairly benign conditions. Could the HP move over the British Isles - possibly but I can't see it moving N or NE on that chart.

GFS finally at the same time from the 00Z OP:

gfs-0-240.png

The most impressive output of the morning for cold fans and it's not hard to see the big differences - the HP is much further north and the ridge is angled NW to link with Greenland heights. It is however quite close to the UK so the message here would be cold and dry with the real wintry weather over Scandinavia. The LP exiting Canada is set to move north keeping the WAA going to the west of Greenland and supporting the heights.

We end up here:

gfs-0-384.png

The heights "find a way" to retrogress N and then NE - the key player is or are very low heights over Europe which block the usual path of the HP into the Continent.

Here's the NH view of the same:

gfsnh-0-384.png

The WAA is now to the west of Iceland but it's a hugely amplified set up with ridging from the north of Siberia (about as HLB as it gets). Western and Northern Europe stays cold and someone will get snow out of that without a doubt.

So we have some themes going forward from this morning - an unsettled immediate period, a possible brief warm up for the south midweek followed by a brief but potentially strong N'ly over next weekend and from there it all depends on where the HP sets up and its orientation. It could sit just to the SW and be oriented to allow the Atlantic over the top or it could ridge north and block out the milder air leaving us in a N or NE flow as heights shift North.

The 00Z GEFS at T+240 are in two camps - those that make the Greenland HP an influence and those that don't and that's reflected in the spread:

gens-22-1-240.png

Plenty of interest ahead I would hope.  

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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

Great find there Knocker, cheers :good:

While the MJO is on the brain for a mo - I noticed just now how the propagation lately has been persistently underestimated by the dynamical models such as GEFS and closer to what the basic statistical models have been predicting;

operdyn_verif8D_small.gif  stat_verif8D_small.gif

Currently the models have the MJO hitting a virtual wall where it is now and decaying. I wonder if this will actually occur or if the MJO will just sail right on... that'd shake up the output at least a little.

Beyond that, we have GFS showing a re-emergence in phase 1 in around 9 days time which would promote blocking to the NW in late March - highly undesirable in my view - while ECM seems to keep it very dead indeed when looking at the H-W plots... of course that could be hiding contrasting signals, such as that from the unusually warm areas in the ENSO region which seems to be driving GLAAM a bit higher than might be expected when considering Indian Ocean MJO activity alone;

gfsgwo_1.png

This could explain GFS being keen to slow the Atlantic down a bit next week. ECM has other ideas although it has backed off a bit with today's 12z.

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

A fine morning here in London after a weekend which was perhaps less of a washout than had been forecast.

It's Day 20 of the 21 since the breakdown of the February cold spell and I'd like to say we were looking at an imminent pattern change but we aren't. After a chilly start to the week, it does look as though the south will have some milder weather during the week though talk of "spring like" conditions looks a little overdone.

Moving on into Cheltenham week and what conditions will await the punters at Prestbury Park on Thursday March 16th:

Starting with GEM 00Z at T+240:

gem-0-240.png?00

Very mobile typical March fare with plenty of PV activity and low heights to the NW and even the Azores HP suppressed so despite transient ridges of HP, a largely unsettled picture.

ECM 00Z at the same time:

ECM1-240.GIF?06-12

Some differences though the broad theme is much the same. A more noticeable Eurasian HP is fading without influencing our weather and while the orientation of the Azores HP is interesting it's a bit of a "no man's land" or col over the south of the British Isles.

GFS 00Z OP at the same time:

gfs-0-240.png

Again, slight differences but not massive. The British Isles is in a cooler W'ly or WSW'ly flow with the LP track running NW-SE across the Faeroes and then down into the Baltic States. Unfortunately, any lingering hopes for heights over Greenland seem for now to have been dashed with the PV not heading for Siberia as seemed likely last week:

gfsnh-0-240.png

Into furthest FI and the LP track changes dramatically as the trough sinks down across the British Isles and into Europe:

gfsnh-0-384.png

Spring definitely on hold if this chart verifies with HP pressure to the SW and NE, the corridor for the Atlantic systems is straight down over the British Isles and into France. Very unsettled with plenty of rain and showers and perhaps snow on northern hills.

The 00Z GEFS at T+240 have plenty of scatter as you would expect but the Greenland heights option appears to have been extinguished to be replaced by HP either just to the west or to the NE and clearly there's been a new signal.

gens-22-1-240.png

The spread reflects the difference between one cluster keeping LP in charge to the west and another slowing down the Atlantic and allowing heights to build near the British Isles but to the west and the NE so the OP evolution far from devoid of support and those of us hoping for some late cold still very much in the game this morning and perhaps the most interesting there are few members showing anything very spring-like.

 

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

A couple of busy days out and about so no time for the detailed report and analysis.

A very pleasant morning here in London after a couple of quite unsettled and wet days which has brought the rainfall totals up though it was a very dry winter certainly compared to recent years.

Spring has sprung but where is the weather taking us ?

Today's analysis takes us to Sunday March 19th and beyond:

Starting with GEM 00Z OP:

gem-0-240.png?00

GEM starts with the jet moving north but it returns south as there is some disruption early next week and to be honest next week looks pretty unsettled and perhaps on the cool side with plenty of rain or showers under quite a cold air mass. The Azores HP is suppressed to the south and secondary features moving across southern counties seem set to bring more prolonged wet weather at times.

ECM 00Z at the same time:

ECM1-240.GIF?09-12

A milder WSW'ly flow for the British Isles with the Azores HP extending a ridge just to the south so drier conditions here but more unsettled and breezy further north. Note the absence of lower European heights compared to the GEM.

GFS 00Z OP at the same time:

gfs-0-240.png

Possibly closer to GEM than ECM at this time but nothing terribly different, A traditional W'ly or WSW'ly flow though sourced from the colder North Atlantic. That said, always drier and warmer to the south while the north stays breezier, cooler and more at risk from rain and showers.

In furthest FI, the OP builds HP across the British Isles as the PV is partially displaced toward Siberia:

gfsnh-0-384.png

There's not much happening in the stratospheric profile at this time as we await the final warming.

Looking at the 00Z GEFS, there's more spread than I was expecting and quite a few colder and stormier options than the OP which suggests the end of next week isn't yet set in stone. A couple of members build strong heights to the NE and while there's no appetite for the Greenland HP option, a lot of members have LP much closer to or over the British Isles.

In conclusion, a couple of warmer, brighter days especially for the south but next week sees a return to something more seasonal with a not terribly mobile WSW'ly flow. It's possible Cheltenham week could be fairly benign but it could also be quite cold and unsettled and that issue hasn't been resolved.

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Evening all :)

A busy life this past week so apologies for the paucity of reports but now it seems I have a little free time so a rare foray for me into the 12Z outputs. After a glorious Saturday in London, a more seasonal albeit still above average Sunday - 14c in  London against a normal early March value of 10-11c. The coming week seems set to continue the early spring theme but for a while the outputs have trended colder and more unsettled into the last third of the month and I still think we will have a colder spell before we get properly back into spring.

Tonight's 12Z output takes us to lunchtime on Wednesday March 22nd which will be six weeks after the end of the previous cold blocked spell.

GEM first of all:

gem-0-240.png?12

A more interesting evolution for fans of colder unsettled conditions. Basically, the LP breaks through into Europe over next weekend and while pressure is building quickly behind it, there remains a cool NE'ly flow.

ECM 12Z Op at eh same time:

ECM1-240.GIF?12-0

Something quite different or just a matter of timing ? An intense LP moving into the SW Approaches with pressure rising to the NW behind it. Hard not to think a GEM-type evolution might follow at T+264.

GFS 12Z OP at the same time:

gfs-0-240.png?12

While the rising of pressure to the west is similar, the northern profile is very different with a strong PV and plenty of energy firing LP systems on a quite northerly focussed jet. Beyond that, HP builds strongly across the country before far off FI shows a different pattern emerging. The NH profiles tell the story - at T+240:

gfsnh-0-240.png?12?12

Note the main core of the PV is over the Pole but there remains energy close to Canada/Greenland but that energy seems to be dissipating. By T+384:

gfsnh-0-384.png?12

A very weak PV almost gone with heights building over the Pole and Greenland and the Azores HP suppressed.

Looking at the GEFS and the picture at T+240 is far from certain:

gens-22-1-240.png

I count six members building heights either in Greenland and ridging SE or around Iceland from the south while the majority of the members keep pressure much lower around Iceland. Clearly, IF we were to see heights around Iceland or to the south, the likelihood of a cool NE'ly flow over the British Isles would increase.

Further into FI and it's worth noting a majority of members are raising heights to the NE - some quite substantially. All of this suggests amplification, a slowing Atlantic and the possibility of interesting synoptics in the last third of the month.

To conclude, a benign and indeed pleasant week ahead - for many, more like May than March but winter or at least colder conditions aren't done with us yet and tonight's output convinces me further there will be a reversion to something much colder and more unsettled in the final third of March.

 

 

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

Back to the 00Z outputs this morning and a quick run through the medium term as we look to next week's developments after what looks like being, as it so often is for Cheltenham week, a generally fine and dry week especially in the south.

Looking at the output for early on Thursday March 23rd and starting with this morning's GEM 00Z output:

gem-0-240.png?00

Picking up from last night's 12Z, the brief disruption caused by the LP diving through the British Isles at the end of next weekend and early next week leads to pressure rising strongly from the SW but with a cut off LP over Iberia there's a light NE flow over southern parts but the Atlantic is gathering to the NW and you'd expect the heights to sink south as the wind backs SW.

ECM 00Z at the same time:

ECM1-240.GIF?13-12

ECM has probably just about got there. The jet is displaced well to the north and it's a benign outlook for much of the British Isles under a long ridge of HP.

GFS at the same time:

gfs-0-240.png

The 00Z OP makes much less of the previous weekend's disruption and maintains a more mobile environment but with the jet displaced a long way north, it's not as much spring but more a summer-like evolution as pressure gently builds from the SW. It's no surprise with an NH profile as such:

gfsnh-0-240.png

The PV remains limpet-like around Greenland and NE Canada but in further FI this starts to finally dissipate a little:

At the very end of FI, we see heights over the Kara Sea and the trough heading SE into Europe but we've been here before many times:

gfsnh-0-384.png

Looking at the 00Z GEFS, only four of the 20 members have some kind of blocking over Greenland or Iceland but that influences the spread over the UK:

gens-22-1-240.png

The Control goes for a large HP to the north of the British Isles in FI with an attendant E'ly over much of the UK.

Out at furthest FI, there's a huge range of solutions as you'd expect but it's fair to say the OP and Control represent the two main clusters so the likelihood of some interesting synoptics toward the end of the month remains this morning.

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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

Just quoting my post over from the MOD thread :ninja:

Just now, Singularity said:

npst30.png  npst30.png npst30.png

A consistent feature of recent GFS runs is for a region of anomalously warm stratospheric temperatures to move across Greenland by Friday and then drift slowly toward Iceland over the following week, where it facilitates a stratospheric ridge. The tendency for high pressure to build back in after a changeable start next week looks to be at least partially in response to this. It is very uncertain, though, to what extent we might see a bit of MJO activity working with or against a ridge in our vicinity - but ECM is keen on having a quiet MJO for the foreseeable and GEFS have backed off recently so it could well be that the stratospheric forcing gets to dominate proceedings. 

It's interesting to see how resilient the vortex is this year despite being so persistently displaced toward Siberia. It makes me wonder whether the severely damaged thermal inversion over the Arctic has made it less 'inviting' to the vortex as a mostly weak but unusually persistent vertical transport of energy drives pulse after pulse of stratospheric warming. Meanwhile Siberia is able to retain an inversion setup due to being a solid land area, making it suitable for a lengthy stay of the vortex core.

I'd wondered whether Greenland could act as an alternative home once the Arctic inversion was lost, but it seems the typical movement of the weak stratospheric warming works against this.

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Afternoon all :)

The equivalent 10HPA for the 06Z OP for next Tuesday (tomorrow week):

gfsnh-10-192.png?6

Signs of the emerging final warming at the end of the month.

 

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Morning all :)

Five weeks since the end of the last cold spell as the HP block retreated rapidly SSE into Europe. I had thought we would be seeing clear signs of the next change in the patter away from the milder Atlantic set up but I suspect the movements in the stratosphere indicated by Singularity above have a lot to do with the fact the PV is reluctant to fully displace and offer the possibility of heights rising to the NW (or indeed NE).

Looking first at GEM 00Z for the early hours of March 24th:

gem-0-240.png?00

Earlier charts showing quite a southward plunge of the jet and attendant LP systems appear to have been overdone and this morning shows a more northerly aligned jet and a fairly uneventful synoptic evolution with a not terribly active Atlantic keeping small systems going W-E to the north of the British Isles. Decent conditions for the south for the most part.

ECM 00Z at the same time:

ECM1-240.GIF?14-12

No Greenland heights at all and although the model makes more of the brief trough disruption at the weekend by the end of next week it's business as usual with a broadly SW'ly flow and the jet well back to the north.  

GFS 00Z OP at the same time:

gfs-0-240.png

Something rather different - HP centred more or less over the British Isles with more than a hint of possible retrogression to heights over Greenland. This was hinted at in the GEFS yesterday. It comes to nothing as a new Atlantic LP smashes through to the south of Greenland and the jet quickly takes over.

The 06Z OP:

gfs-0-240.png?6 

HP in charge but a much more mobile and flatter scenario with a strong northern jet sending LP well to the north of the British Isles.

The 06Z GEFS show plenty of spread:

gens-22-0-240.png

The Greenland HP option isn't dead and it would also be fair to say there's a solid minority with colder air over the UK.

That being said, there's been a clear step away from some of the colder options being shown yesterday (the 00Z OP being an exception). The PV continues to weaken as the month progresses but doesn't displace favourably so it may well be that this year March will come in like a lamb and go out like one as well. None of this means there can't or won't be a late cold spell in early April but the odds have lengthened somewhat this morning and it may be we'll have a long spring before a move in to summer.

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Posted
  • Location: Cleeve, North Somerset
  • Weather Preferences: Continental winters & summers.
  • Location: Cleeve, North Somerset
1 hour ago, stodge said:

 

That being said, there's been a clear step away from some of the colder options being shown yesterday (the 00Z OP being an exception). The PV continues to weaken as the month progresses but doesn't displace favourably so it may well be that this year March will come in like a lamb and go out like one as well. None of this means there can't or won't be a late cold spell in early April but the odds have lengthened somewhat this morning and it may be we'll have a long spring before a move in to summer.

Loving your updates stodge, keep them coming! I may just point though that March came in anything like a lamb here haha.

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Posted
  • Location: East Ham, London
  • Location: East Ham, London

Thank you for the kind word, my friend :)

I can't hope to compete with the expertise of Matt Hugo so I won't. If you want some real weather knowledge, read his blog. If you want the ravings of an enthusiastic amateur, read on.

A gorgeous morning here in London and a promise of another fine, spring day with temperatures likely well into the mid to high teens.

Does it continue or do we cast a glance back toward winter - let's see ?

Looking to the early hours of Saturday March 25th on this morning's output and starting with GEM:

gem-0-240.png?00

We've been here before - a brief N'ly or NW'ly immediately precedes this but there are no heights to the north to sustain the ridge and there is enough energy for a gentle toppling of the ridge which is starting - a cool NE'ly to southern and eastern parts of England and Scotland but the wind is backing SW'ly over Northern Ireland.

The problem is this chart and evolution has been shown before by GEM this winter and hasn't verified so we'll see...

ECM 00Z at the same time:

ECM1-240.GIF?15-12

You'd be forgiven for thinking this was GEM at T+264 - it's certainly a more than plausible continued evolution and apart from timing (ECM is more progressive), the two models are very similar in synoptic evolution this morning.

GFS 00Z OP at the same time:

gfs-0-240.png

Recognisably similar though the evolution to this point is very different. GFS models a much stronger northern arm with the jet displaced a long way north which has allowed LP in the classic Gulf of Genoa area.

Looking at the NH overview of the same timeframe:

gfsnh-0-240.png

The PV very much at home in its usual home so no chance of heights over Greenland but a chance (given the orientation of the PV back across the Pole) of Scandinavian heights and further into FI, a brief Scandinavian HP develops before the PV is displaced toward Siberia at the very end of the month:

gfsnh-0-384.png

Again, we've been here before. Vortex displacements are frequently modelled but rarely come off as new micro-warmings send the vortex back to Canada/Greenland. Could heights build into Greenland in early April ? Wouldn't be unusual but it's a very long way off.

Looking at the 00Z GEFS at T+240 and it's a very anticyclonic story with most members having HP near the British Isles and, it has to be said, quite a few having that blocking to the north (including NE and NW) - I count seven members having the core of blocking to the north of the British Isles so not to be discounted and others have a strong anticyclonic bias with the HP centred just to the west or right over the British Isles.

To conclude, plenty of dry HP weather looks the call after the trough disruption at the weekend coming and early next week though the centre and orientation of the HP is far from clear and, as ever, more runs are needed.

 

 

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