Model discussion highlights

[Mike Poole]

2 minutes ago, damianslaw said:

Just musing but doesn't a SSW result in a flushing out of the westerlies so to speak before its affects imprint fully.

It does usually, when it’s on the back of a strong strat vortex, but there aren’t any significant westerlies there to flush down in this case, because of the weak strat vortex all winter, and of course the previous SSW in January.

For example, GFS 12z zonal winds:

If there were strong westerlies to flush you’d see a strong pink anomaly (right chart) in the lower strat moving down with time with the blue anomaly from the reversal above it.  It isn’t there.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5036863

[Cambrian]

Both the EPS and GEFS have moved away from the idea of a strong Scandinavian / NW Russian trough being established at around day 8. 

Comparing charts for the 22nd, at day 10 from Monday and day 8 from today’s 0z runs. 

EPS 

 

GEFS

 

Both suites appear to have underplayed the Atlantic troughing, both immediately to our northwest and upstream towards NE Canada. 

GEFS has been overplaying heights rises at day 10 further north in the Atlantic and through Greenland. EPS did a better job of those at day 10, but overplayed the heights through Western Europe.

Inter-model convergence, along with loss of wide ensemble spread, is a good indicator of the point at which these models become more reliable. This appears to be at around day 8 for this particular period. 

Both models have adjusted upward the activity of the Atlantic jet stream, and both would now seem to be indicating a spell of a NW-SE aligned jet stream running south of the UK and Ireland and down into Europe, around the base of a trough around Iceland. Day 8 GEFS. 

 

The overall take on looking forward from there at day 8 through to the last week of the month fits nicely with the ideas on the strat and the clusters.

For me, possibly a bit more to play for in the event than looks firmly on the cards at the moment. 

Rather cold and changeable for northwest Europe, scope for systems that develop over Greenland wrapped up in cold air, to run down the western flank of the trough. These feeds typically contain pockets of colder and less cold air, as systems pass through. It’s not a bad time of the year for some wintry episodes from that quarter.

I’ll be keeping an eye on how cold the lows heading out of Greenland will be, some wintry weather at times from this setup looks a fair possibility, and definitely more so than for the month up until now!

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5037414

[Kirkcaldy Weather]

Wanted to do this post which will be addressing those who continue to disregard us who use the teleconnective aspects.

A few crucial areas here which have been prominent for weeks.

• The Stratospheric Warming - Sudden Stratospheric Warming didn't 'fail' I've already shown the timeframe in which this reversal of zonal winds at 10hpa DID occur I'll link that post below.
• The MJO progression didn't 'fail' or become 'unsupportive' those who regularly follow my posts can gleam that the MJO and resultant patterns have been in line with expectations.
• Winter 2023>2024 hasn't 'failed' or been a 'bust'
• There hasn't been any occasion of being led up a 'garden path'
• The teleconnections as a whole haven't 'failed' or been 'misleading'

 

Latest data on the El Ninò temperatures are in at +2.2C which takes the 2023-2024 event into Super Ninò status. (Credit JMA)

December 2023 monthly heights

January 2024 heights

Typical heights during a strong El Ninò

The warm and cold episodes have correlated excellently in line with the Arctic Oscillation 

Leading on from this post

 

'We'll continue seeing patterns which link to El Ninò throughout March and I'd favour potentially the first few weeks or so of April, following that time it's a gradual move into ENSO Neutral with some themes continuing of heading into La Ninà by late spring and particularly Summer 2024.'

Doing a VERY extended outlook.

We see the transition from El Ninò >> La Ninà again everything pretty much as expected of course I'm showing an 8 - 11 MONTH period here so will it resemble this 100% probably not to a T but overall good representation.

Note the precip changes which are particularly noticeable in Australia and the Southern United States

This shown very well globally on CANSIPS

This switch also displayed by looking at the 200hpa U-winds

And with the 500hpa heights

And of course one of the most important the Sea Surface temperatures 

Whilst the MEI is one part of the ENSO spectrum we see that this Ninò has been running effectively parallel to 2009-2010 [also 1991-92 to some extent] which adds credence to that being my #1 analogue through this winter and the hurricane analogues continue showing this.

Returning to February we've got a couple of significant 500hpa evolutions to watch as the same cyclonic system which became the significant winter storm across multiple US states, this looks to be the main influence across the UK & Ireland by the 22nd & 23rd.

Goes with expectations with a strengthening positive NAO.

Following on from this I'm seeing a trend for a possible transition into yet another of the precursor setups for further stratospheric warming.

Current timing looks to be the very last days of February into March week 1.

Thanks for reading. KW

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5037585

[Mike Poole]

14 hours ago, LRD said:

Agreed. The ECM clusters have been useless this winter (and last). But they're anomaly charts which are not to be trusted in the slightest.

Just to correct this point.  One of the main benefits of the clusters presentation is that they are not mean charts - i.e. the  charts are representative members best representing each identified cluster.  So they are physically real, and not some averaged mess.  While the shading is indeed an anomaly, the height contours are not - they are the actual height contours of an individual run.  So the best way to read them is, yes take the colours as a guide (if they are dark colours) but bear in mind they are an anomaly, but look in detail at the height contours which give the upper wind flows which are real.  For example, here’s today’s T264+ chart:

Look at the top right one, cluster 1 T360, here is the representative member at that time:

You can see that the height contours on the cluster plot match the height shading on the Meteociel plot.  

The clusters are a probabilistic representation - whether any of the clusters at day 10-15 have actually included the weather that eventually verified is a question that needs to be answered probabilistically (my view is sometimes, but quite often this winter they have showed blocking with quite high probability that hasn’t happened).  But that is a judgement on the verification of the EPS, not because part of the cluster chart shows a shaded anomaly, as I say, when reading them it is best to focus on the contours.  

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5037908

[johnholmes]

Well a long time since I created a post using the usual models ( 2 Feb the last times)

In brief for approximately 23-27 February all 3 are on the same page. They show a marked upper trough over the UK edging slowly east and warming out slightly. On the surface ECMWF shows a deep low just south of Iceland on day 1 (27Feb), NOAA shows a marked 500 mb trough over the UK from a flabby sort of main trough NE Canada/NW Greenland by 26 February. UK Met 20-22 February shows a similar pattern with a marked upper trough and surface feature over the UK.

NOAA has contours on its 6-10 over the UK from about 520-534 DM north to south over the UK. So cold by the average expected for late February. ECMWF shows a quite strong northerly pulling in the cold air, surface and at 500 mb. UK Met by its last date (22nd) shows a strong NNW’ly over the near Atlantic with a rather flabby low over the Northern Isles and a high west of the NNW’ly flow.

Further ahead ECMWF indicates an upper ridge moving east into the SW along with a surface high a bit west of 20W at the same latitude as northern Spain.

NOAA with its 8-14 day chart has a +ve height anomaly of 150 DM or so in about the same place as the ECMWF surface high.

These charts would suggest that by the 27-28 February the cold air supply is being cut off. Probably by next Saturday ‘deepish’ cold air will be covering most parts, say -4 to -5 C at 850mb. I would think these conditions lasting until about month end?

Just my take on the outlook!

I'll try and post the charts I used to arrive at this

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5038707

[carinthian]

 Daniel*  I just hope that charts comes to fruition next week. Currently , over here in Austria heading for the warmest February ever ! Yesterday saw a record 13.9 c recorded at 2400m , the warmest at that elevation for February  since 1961 . Quite widely 19 c recorded at 400m on Friday. No wonder when 37c plus being recoded during this month in Morocco. Something very wrong !

C

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5038951

[Kirkcaldy Weather]

 

Following on from this post and honing in on the 22nd - 23rd to begin with.

I've discussed in the past there are multiple pathways to cool - cold conditions in the UK and this will excellently fit into the cool - cold STORMY category, we've got the continuing influence of a strong positive North Atlantic Oscillation pairing with a strengthening positive Arctic Oscillation which will see the prior US snowstorm track into the UK as a very deep trough with means being indicative of the region of 960-970 hpa being reasonable estimates though lower pressure readings at the core of the trough cannot be discounted.

This will be a section of the Tropospheric Vortex.

With these setups it's a case of everything and the kitchen sink Thunder hail gales where the isobars are tighter and with increasingly Lowering thickness snow though being most prominent over high ground will mix in at lower levels

From the 24th current data shows this trough will gradually weaken as it moves south across Europe likely becoming a cut off low into Italy and the Mediterranean.

There then becomes a few discrepancies with how quickly we see a link with the increasingly strengthening high pressure into the Maritimes and Eastern US [strongly negative PNA] and the blocking to our East Northeast > MJO phase 6 / 7.

This is a combination of teleconnective feedback we haven't had at any point during winter 2023>24 with this being the strongest negative PNA since October

Focusing on developments in the stratosphere too, overall I'm really happy with how my post below has went with the precursors doing a great job again

 

• Reversal of zonal winds at 10hpa 
• Displacement event at 10hpa
• Split event at 50hpa
• Split event at 100hpa

With further precursor patterns there are already signals of new stratospheric warming heading into March

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5039236

[damianslaw]

The remainder of February set to stay mostly unsettled ending what will go down as a very unsettled, dull and very mild month. However, a change from very mild to closer to average is on the way Thursday onwards, quite probably continuing into March as we see the atlantic trough amplify and push azores high out west.

Becoming very wet, windy at times, snow on northern high ground and light frosts in any sheltered areas in northern and central parts thanks to polar maritime air. Its the type of set up that can bring bright brilliant blue sky one minute then a sharp blustery hail shower the next and generally a cold feel. 

Longer term, just hints we might see more concerted northern blocking calming things down somewhat but not clear whether will be cold or nearer average with the jet riding across the UK bring cyclonic conditions.. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5039953

[Kirkcaldy Weather]

Lots going on.

As the initial deep cyclone moves in through tomorrow there will be a few developments, along the southern flank there will be spawning of additional cyclonic centres thanks to a strong Jet Stream which already broke records when it was situated over Northeastern America 

 

During the initial phase of cyclogenisis the newly developing cyclonic Centre running through central and South Southeast England will have 2 zones of convection with one being particularly prominent and linear in form... possible Line Echo Wave Pattern / Squall and additional thundery cells could develop ahead of this line.

There might be some flash flooding within this.

During tomorrow I also wouldn't be shocked seeing flash flood reports across France. 

Into Friday this develops into 3 cyclonic centres with the one from the UK undergoing rapid cyclogenisis as it moves over the North Sea and swings into Scandinavia as a deep snowstorm which links to the original main cyclonic Centre which is part of the Tropospheric Vortex. We also see another cyclonic centre developing into the Alps as a snowstorm too.

As the linear convective activities clear into the North Sea the thickness level across Ireland and UK lowers with a plethora of wintry precipitation and snow even at low levels with laying snow a distinct liklihood particularly across Scotland Thundersnow opportunities likely too.

For the next developments we need to go back to the low which brought flooding rains across Florida.

This same cyclone will deliver further snow in Newfoundland 

This same cyclone will move over the Atlantic high and become joined with the original cyclone / section of the Tropospheric Vortex North northwest of the UK this will move toward Ireland the UK and Europe by Feb 25th / 26th.

During this timeframe the Alps snowstorm will be directed Northeastwards with current guidance of a snowstorm(s) ranging from Denmark and especially Sweden to other Baltic countries such as Latvia and Finland. 

The new system moving into Ireland UK and Europe could bring new flash flood risks from Southern England, Portugal, Northwest and North Spain into France once more... track and hpa dependant possible gales too.

As the high to the east builds into a high in Scandinavia this will connect to the Atlantic High giving the cut off low by February 26th - 27th.

This connection will be brief at this stage with new trough developments close to the UK & Ireland During the last days of February into the beginning of March

During week 1 of March with further influence from phase 7 of the MJO this could see further connections between the Canadian Maritimes Blocking and the Block to our East Northeast with potential this evolves into a Greenland High a la 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5040369

[WYorksWeather]

Still looks like knife edge stuff as to whether the February CET record will go. A milder incursion around the last couple of days of the month could prove decisive, but equally some cold nights possible before that.

Beyond that, into early March, there's still far too much scatter to say anything with any certainty in my view. Possibly the only clear good news is that we look to get a solid rise in pressure into March. Mean now gets us to 1020mb.

Looking at March more generally - in winter we often tend to focus on the cold pool, but I also think it's interesting to look at the available warm pool. It's an incredible pattern for the time of year. The first chart is tonight's GFS 12z for the 10th March. The black outline in red is the +20C isotherm area. After that, we have the equivalent charts for 2023 and 2022.

2022 is perhaps closest to this year's chart, but the extent of the 20C isotherm is still far greater this year. It's really quite extraordinary to see. To make the point even more, here is the GFS for the 6th of April 2023, which is the earliest chart I could find from last year that looked similar! We're nearly a month ahead.

More local to us, it's also notable how little cold there is to our east. Even if we do get an easterly, it would need to drag the cold a long way west, and perhaps more south-west. There's nothing much to work with over central Europe, we need to go all the way to Russia or north to Scandinavia to find anything of note.

Interesting to watch this going forward, but it is a key factor. We need to be looking not just at the synoptic charts, but also the actual amounts of warmth or cold available.

We then have the SSTs to consider. Here we are at days 0, 5, 10 and 15 from the ECM, both the absolute values and anomaly view. Absolute SSTs are now bottoming out, and the anomaly view clearly shows that the warm SSTs near the Azores are not going anywhere any time soon.

   

Summary

In short, continued cold / near average and wet for the time being. Bit of a drying trend into March, possibly an early signal for warmth, but nothing too out of the ordinary really for the time of year.

Looking at a much broader scale though, the amount of warmth available this year is really quite something. If that does start to filter into parts of Europe, the risk increases that at some point we tap into it. Warmth is therefore very strongly favoured, though of course not guaranteed. I think it will be very tough to get any prolonged spells of below average temperatures for as long as the wider Northern Hemisphere temperature profile remains so warm.

 

 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5041266

[carinthian]

Evening all , just looking at that latest chart for months end. Another pulse of warm air heading into The Eastern Alps. So far up to 25 th Feb , it is the warmest February ever in 257 years of records kept in Austria. Nearly a massive +6c  above the 1991-20 average ( that is also a period of warm decades ) Some parts of Austria not seeing any snowfall at all this winter. Quite astonishing.

C

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5042254

[MattH]

 TillyS

This post in itself is misdirection...

One failed evolution linked to previous discussions regarding the teleconnections and the likes of the GSDM and people then suggest they are not reliable, rubbish. There have been a handful of cases throughout the winter when the connections between these and the sensible weather on the surface have played out well. There's a saved post of mine from weeks back, highlighting the connections between the evolution of the GSDM and the waxing and waning of the AO through Dec and Jan, when we experienced both very good examples of +ve AO and -ve AO events. This last 'failure' is seemingly linked to a highly complex setup due to stratospheric interference and reflections - https://climateimpactcompany.com/daily-feature-introducing-a-new-index-to-help-forecast-polar-vortex-arctic-air-episodesstratospheric-downward-wave-reflection-events-2-2/ possibly, amongst other things too, but aren't worth bothering discussing.

You can't win them all...

You're right about the models mind and that includes the full suite of NWP, not just those three models, if you're looking at the short-term, then everyone should be looking at the ECM, UKMO et al.

Regards, Matt.

 

 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5042443

[Kirkcaldy Weather]

 

Extremely pleased how the patterns have & are developing there's a few timeframes I'm focusing on ATM.

On 21/02/2024 at 20:17, Kirkcaldy Weather said:

This connection will be brief at this stage with new trough developments close to the UK & Ireland During the last days of February into the beginning of March

 

On 21/02/2024 at 20:17, Kirkcaldy Weather said:

During week 1 of March with further influence from phase 7 of the MJO this could see further connections between the Canadian Maritimes Blocking and the Block to our East Northeast with potential this evolves into a Greenland High

As this next low becomes a cut off low first across the UK and Ireland with below average temperatures at 850hpa and surface levels with fronts wrapping around the low this brings potential for snow event(s) for the UK and Ireland.

I had mentioned in a number of my posts that week 4 of February was the next significant opportunity for patterns which could favour wintry conditions and I'm extremely happy seeing such evolutions.

As the thickness levels begin to lower once more this sees the showers from the Atlantic becoming steadily more wintry and once the low begins to develop into that of a cut off and the cold air continues to intensify as it undercuts frontal precip current trends show potential for snow event(s) in particular for Wales, Northwest and Northern England [Pennines] and pushing into Scotland.

In these areas seeing snow / wintry precip there will also be frosts and an ice risk maybe even an ice day with snow cover.

As the pattern across our side of the Northern Hemisphere begins to develop retrograding tendencies we'll see a few big and interesting developments.

As a high which is currently building further to our East begins to strengthen once the retrograding begins this will move westward to sit to our East also during this our cut off low also retrogrades westward into the Atlantic, this combination suggests a plume setup during week 1 of March is a real possibility.

Into week 2 of March with further retrograding the connection of blocking to our East Northeast and the -PNA high across East Northeast America and Canadian Maritimes begins to centre in across Greenland.

With the MJO having progressed across the Western Hemisphere, South America and Africa and currently residing within the Indian Ocean this gives feedback in line with the above patterns and suggests there is a possibility for a colder flow from the Northeast > East though how much influence this has in the UK TBD. 

Plenty of interest as we head closer to Mid March I suspect.

This ongoing cycle of the MJO carries importance with regard to El Ninò though there are still a bit of discrepancies with how amplified the MJO becomes within the Indian Ocean with the GEFS seeing a strong event whereas the CFS is much less amplified.

The GEM & JMA are more akin with the GEFS

I'm more familiar with Westerly Wind Bursts which are the warmer ones however we're looking at Easterly Wind Burst event here which could further speed up the ongoing decline in the El Ninò temperatures.

 

Also worth noting once more with the precursor patterns continuing we've got good signals for a new reversal of zonal winds at 10hpa (possibly 50hpa though no agreement on that just yet) with this looking like a stronger reversal than the previous 2 of winter 2023-2024.

Thanks for reading. KW

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5042615

[Cambrian]

The end to another week marked by another cold trough dropping down from the north over the UK and Ireland, 12z GFS op, 0-78h. These are the 500mb temperature and heights charts. Nice to look at.

Last week’s colder snap flattered to deceive in many ways. The impressive looking 528 dam thicknesses only delivered for the tops. I must admit that I saw more scope in it for snow than transpired. 

This one will perhaps prove more interesting in the event as there is a low pressure system with its own circulation that forms at the base of the trough. The trajectory of arrival is more sharply NW-SE so there is slightly colder air wrapped up in it, with heights as low as 512-520 gpm, and there is also more organised precipitation.

This time there is a keen ridge building behind the low, which serves to cut it off from the trough at least for a while, until it merges west with the base of the next incarnation of the Greenland longwave. 

The models have struggled all week with the rate at which the low gets warmed out, with a trend over the last few days toward keeping it that bit colder for longer. @Ali1977 has been picking up on this firming up over the last few days. 

In any case, there’s certainly plenty of weather around on Friday into Saturday in particular, at 36-78h, as the low pivots its way through Ireland and the UK and spins out a secondary system to France. 

 

It’s made more interesting by the system arriving during nighttime hours and the relatively slack circulation as it grinds to a halt possibly aiding some evaporative cooling at times with the heavy and sustained precipitation, so maybe the first couple of days of spring this year might well have a decidedly wintry feel. 

Very likely my last post of the winter! I have greatly enjoyed it, though it seems that the models we study are possibly on as steep a learning curve as we are. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5042832

[Kirkcaldy Weather]

On 21/02/2024 at 20:17, Kirkcaldy Weather said:

During week 1 of March with further influence from phase 7 of the MJO this could see further connections between the Canadian Maritimes Blocking and the Block to our East Northeast with potential this evolves into a Greenland High a la 

 

On 27/02/2024 at 21:05, Kirkcaldy Weather said:

As a high which is currently building further to our East begins to strengthen once the retrograding begins this will move westward to sit to our East also during this our cut off low also retrogrades westward into the Atlantic, this combination suggests a plume setup during week 1 of March is a real possibility.

Starting at this point looking into the dynamics at play, as the Atlantic High moves eastward into Spain this will connect to the high developments to our East - Northeast from the south Southwest which does give a plume style pattern though brief. 

For the 2nd part of dynamics leading to the strengthening Blocking this comes thanks to the recent impressive strongly -PNA which was the strongest negative phase we've had all winter.

As the -PNA high energy moves into the block to our Northeast there are indicators this may become at / record intensity of hpa for this timeframe with blacks and purples which are particularly useful spotting these.

Leading on from my post here 

 

"Following on from this I'm seeing a trend for a possible transition into yet another of the precursor setups for further stratospheric warming.

Current timing looks to be the very last days of February into March week 1.''

Very happy with those estimates

This gives a boost to the stratospheric warming which is ongoing with feedback of this setup into a strong warming event during March week 2.

So looking in some detail at some of the evolutions from now through the first half of March.

We've got some wave break action which causes an upper level cold pool to move roughly northwestward from Europe to the North Sea 

As the High begins to retrograde this sends its accompanying wave break low / upper level cold pool northwestward whilst our cut off UK - Ireland trough also creates further cut off low developments into Italy.

As I've been covering in my recent posts my main interest with regard to opportunities of below average conditions from the Northeast and East has remained focused from week 2 of March.

With the Scandinavian Block continuing its retrograding movement west northwestward to Greenland blocking this will open the door to exactly the above.

With a deep Atlantic trough and a Southerly tracking Jet Streak this will see plenty of colder than average temperatures at surface and upper levels (some significant) tracking across Southern Europe and parts of Northern Africa, those who follow my posts may remember various times during winter which produced flash flood risks across Portugal, Spain and progression further east... this is another prime showcase.

Where the 500hpa setups will evolve to in a weeks time is perfect to where I'd expect to be given all teleconnective feedback which includes the prior stratospheric warming(s) feedback

Following onto my post above.

This is an impressive MJO cycle with a strengthening amplitude from the Indian Ocean which looks to maintain amplification as it crosses the Maritimes and heads into the Pacific. Having discussed upto phase 2 we are beginning to have feedback of phase 3 heading from March week 2 > 3 with the storm track in America gradually shifting northward and the trends into cut off blocking with troughs either side and possibly stormy conditions.

 

Absolutely gorgeous.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5045052

[Cambrian]

Some indications emerging now of how the aftermath of the SSW might play out in terms of the Northern Hemisphere profile over the next couple of weeks. 

The 0z ECM ensemble mean / EPS charts show low pressure centred near the Low Countries at day 4. The Scandinavian heights are being squeezed northwest towards Greenland. Strong heights in this region appear to be a feature of the next couple of weeks.

 

They are being held there at day 7 by a westward extension of the Siberian core of the PV to the north of Greenland, which reinvigorates the Greenland trough, bringing the western fringe of Europe to the eastern periphery of an Atlantic cyclonic influence. 

 

By day 10, this westward extension of the PV has developed further, forming a major trough down through eastern North America, a very cold spell looking to develop there,

 

peaking at around day 12, while Europe remains quiet with temperatures near average.

 

Indications of a change for Europe by day 15 though, as heights rise through the Atlantic and a Scandinavian trough becomes established, along with a surface low over the northern Mediterranean…

 

…bringing signs, albeit at that distant range, of scope for a northerly surface flow, picked up on the EPS MSLP charts too, flowing from the Siberian Arctic, through the Norwegian Sea, to Western Europe. 

From what has proved at times to be a quite exasperating winter, though the Atlantic might at times dabble with us, it looks like we’ll move towards and pass the spring equinox with a largely blocked setup and one more tease for prospects of cold weather, this one perhaps being directed rather than being diverted by events in the stratosphere. 

Relatively quiet it almost certainly will be. As for something notably cold later in the month, well maybe, but let’s not hold our breath!

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5045896

[Cambrian]

We are ten days away from the spring equinox. Looking at the 0z ECM ensemble mean for day 10 shows a much depleted PV. 

If we imagine a line running west-east across the Arctic dividing the hemisphere between the Greenwich meridian half and the International Date Line half, a continuation of 90 degrees west over the pole to 90 degrees east in longitude, we see that the PV is entirely on our side of the hemisphere. 

An Alaskan ridge extends all the way through to the far east of Russia so the core PV is being squeezed to the Greenland-Svalbard-Kara Sea region. 

  

The core cold sits further west over northern Greenland. There are two main zones of polar troughing being orchestrated, also shown nicely on the 0z EPS chart, one running south through the Norwegian Sea, and a really handsome one, with an easy run south for the cold air over the continuous ice / land mass of the Canadian Arctic down into the eastern United States, much easier than over the long sea track down into Western Europe. 

As a result, the T850 -4 degree isotherm and 540 dam heights contour runs from Washington DC at 39 degrees North to just north of the central belt in Scotland at 57 degrees North. 

Nevertheless, in this same broad setup, that is maintained for a fair few days thereafter, especially when the trough sets in just that little bit further east over Scandinavia, there are possibilities for incursion of cold air into Western Europe too, as here on the 0z ECM control at days 11 (a clean northerly shot there) 

 

and day 13/14 (a bit more messily cyclonic but still cold).

  

I’m enjoying the longer and brighter days at the moment and it’s interesting to see some warmer southerly episodes cropping up in the ops.

However, I really like the ECM for the way that it typically keeps the control (in effect the post day 10 op) synoptically coupled to the mean, even at the longer ranges - it’s better than the other models in this regard - so for me, with this polar setup, and in many ways, typical for the time of year with waning PV and marked long wave troughs, some colder weather is still very much a distinct possibility for the last third of the month.

Indeed, in keeping with the above, it would be little surprise to see stark and sudden transitions between warm and cold spells over the next few weeks. Happy Mother’s Day.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5046768

[Cambrian]

Here at day 5 on the 12z GEFS, as we’ve seen several times during the last few months, the hemispheric profile achieves a striking north-south orientation of heights, the PV with its core over Siberia coordinating a Scandinavian trough,

 

which combined with cross-polar heights at the merging of Alaskan and Atlantic ridges, delivers us a handsome northerly flow.

But as during the winter, it’s brief. The pattern has no hold. By day 10, the PV relaxes, the Siberian core leaks out west again towards northern Greenland, so the pattern falls lateral again and the reinforcement of the Greenland trough drops a low pressure southeast out of Greenland. 

 

The Alaskan heights are squeezed out, and there is a complete reversal over the Atlantic - with a 40+ dam drop in heights over 5 days to the west of the UK and Ireland, we’ve swiftly lost the Atlantic ridge and we’re back into an Atlantic cyclonic pattern heading into Easter. 

And as during the winter, once it’s set up, this pattern is not brief. By day 15, there are heights to the north but the PV is lateral, and still very much on our side of the pole, preventing a full build, so instead, we get a southerly tracking jet stream brewing up systems carrying a lot of moisture running up from the southwest, through the corridor paradoxically being held in place by the northern heights.

 

It’s as we were then, seemingly too far south for the northern heights to bring us blocked cold, and too far north for the southern heights to send us a proper block, so we get a fleeting Atlantic ridge that can’t form a robust block with the heights to the north, because they themselves lack sufficient traction, followed by the PV and shallow heights to their south then going lateral and serving us up another extended run off the Atlantic.

Fair enough to point out that is what we would expect for a temperate Atlantic climate but the unrelenting nature of never more than a few days with any other option on the table, at the moment at least, seems quite grimly exceptional. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5049100

[Cambrian]

There’s often comment on here regarding the reduced reliability of the models past a given timeframe. 5 days is often stated as the point at which models become unreliable.

Studying the ECMWF web pages, it would appear to be a good deal more nuanced than this.

They publish charts showing the “Continuous ranked probability skill scores (CRPSS) of forecasts of upper-air parameters by TIGGE centres”, with the following notes about the score being used:

The Continuous Ranked Probability Skill Score (CRPSS) is a measure of how good forecasts are in matching observed outcomes.   Where:

CRPSS = 1 the forecast has perfect skill compared to climatology - forecast beneficial;

CRPSS = 0 the forecast has no skill compared to climatology) - forecast has no benefit over climatology;

CRPSS = a negative value the forecast is less accurate than climatology - forecast misleading.

CRPSS is evaluated by calculating the function  CRPSS = 1 − CRPSforecast / CRPSclimat where:

Continuous Ranked Probability Score for the forecast (CRPSforecast) is calculated comparing the Cumulative Distribution Functions (CDF) for the forecast against observations (or analyses) over a given period. 

Continuous Ranked Probability Score for climatology (CRPSclimat) is calculated comparing the Cumulative Distribution Functions (CDF) for the forecast against climatology over the same period. 

Hersbach, H., 2000: Decomposition of the continuous ranked probability score for ensemble prediction systems. Wea. Forecasting, 15, 559-570.

Here’s the link to the paper that ECMWF cite:

https://journals.ametsoc.org/view/journals/wefo/15/5/1520-0434_2000_015_0559_dotcrp_2_0_co_2.xml

From the cited paper, excerpted: Instead of two options (event occurs or does not occur), the range of the parameter of interest is divided into more classes. In addition, the RPS contains a sense of distance of how far the forecast was found from reality. For a deterministic forecast for instance, the RPS is proportional to the number of classes by which the forecast missed the verifying analysis. Although the choice and number of classes may be prescribed by the specific application, the exact value of RPS will depend on this choice. It is possible to take the limit of an infinite number of classes, each with zero width. This leads to the concept of the continuous ranked probability score (CRPS)…This CRPS has several appealing properties. First of all, it is sensitive to the entire permissible range of the parameter of interest. Second, its definition does not require…the introduction of a number of predefined classes, on which results may depend….Finally, for a deterministic forecast, the CRPS is equal to the mean absolute error (MAE) and, therefore, has a clear interpretation.

 

This is useful because:

1. Rather than the (subjective) right or wrong, we have a graded measure of the extent of deviation from the realised outcome. 

2. Any score above zero demonstrates some forecast skill over the assumption of climatology. 

 

Here are the CRPSS charts for T850 and 500hPa height for the Northern Hemisphere incorporating data for the winter just ended. At day 5, ECM attains a score of 0.62 for T850 and a score of 0.72 for 500hPa geopotential. The score for heights is higher at day 6 than that for T850s at day 5. 

 

The timeframe above the 0.5 CRPSS level (where the forecast matches the observed outcome in more instances than it doesn’t, compared to climatology) corresponds to between day 6 and 7 for T850 and between day 7 and 8 for heights. 

At day 10, the score is 0.28 for T850 and 0.33 for 500hPa height. Both those scores continue to offer reasonable “value” at day 10, though to be fair, at a level less than half the value offered at day 5.

By day 15, the score is around 0.12 for T850 and near 0.15 for 500hPa height, much lower, but still above zero so exhibiting some skill when compared to just assuming climatological norms.

The ECMWF appears to put some store in the 0.25 or 25% level, as this is what they use to illustrate the improvement in skill over the last 25 years. This graph is great.

It shows the lead time in days before the score drops to 25% and is for T850. The model has the same level of skill at day 10 in 2024 than it did at 5.5 days in 1998. Noticeable too that winter T850s appear to be handled better than summer ones, probably due to the winter PV, with typically fewer meridional episodes and less dramatic fluctuations in the winter as a result. 

In summary, in our parlance, the models are more “reliable” for longer for predicting heights than they are T850s. For heights, these are typically of sound merit all the way out towards forecast day 8. 

The reliability drops off steadily from day 0, there is no sudden drop at any point and the forecasts maintain some predictive value when compared with climatological expectations all the way through to day 15, which is presumably why this timeframe is catered for in the outputs. 

Lastly, and perhaps most excitingly, the models appear to be better now at day 10 than they were 25 years ago at day 6. 

This all fits very nicely with the general narrative surrounding their use here in the model thread. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5049286

[Cambrian]

Hats off to the models. They had picked up on the deepening trough in the nearby Atlantic on the run-up to Easter about a week ago. Not a great outcome in terms of the weather, but the UK and Ireland in the box seat for observing some industrious cyclogenesis over the next 4 days, here on the 0z ECM op.

Interesting to see the two packets of low heights dropping out of northeast Canada, the second one really packing a punch and deepening the low pressure to around 965mb, as it spins around nearby giving us all a good wallop, centred to the northwest of Ireland by Thursday. 

The 0z ECM mean anomaly chart for day 5, Good Friday, shows the problem for the Easter holiday in the form of the trapped trough, held firmly in place for several days by a bank of heights pushing up over the western half of the Atlantic and the other bank stubbornly holding on over the eastern half of Europe. 

 

The western Atlantic heights look to ultimately prove the stronger, migrating north to Greenland by day 10, squeezing the trough to the north through the Norwegian Sea as the eastern European heights get slowly nudged into Russia, allowing the surface low to move through to Germany, bringing the UK and Ireland into a northeasterly flow. 

 

So looking like we’ll eventually get rid of the poorly timed unsettled spell for something a bit drier and chillier. Yes, hats off to the models but I’ll definitely be keeping my hat on.

 

At this time of the year in particular, with the full range of weather that the spring can offer, the choice of hat is indeed a valuable indicator of how it’s going. Clearly far too early for the time being to venture to the apparel shown on the left, looks like I’ll be sticking with my reliably functional fisherman’s beanie for now. Have a great day. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5050682

[BlueHedgehog074]

I think the below would explain the sleet and snow reports for some of you in the South-West of the UK, even for lower levels.

Using examples at both 10pm and 11pm on the 18Z GFS, it has places such as Devon just on the Western flank of the little circular disturbance/Low drifting North from the main Low to the South-West of Ireland. It also means some of you guys down South-West end up being under somewhat colder 850 hPa temperatures between -1*C to -3*C. That, along with the precipitation being particularly heavy towards Western/South-Western parts of the UK (as well as the fact that the temperatures at the 500 hPa level are very cold with those blues and purples - essentially a very deep upper trough) is likely aiding in dragging down freezing air to low levels in some places, thus the surprise sleet and snow some of you are getting. Especially over higher ground. Though I don’t consider myself to be an expert, that’s probably the reason for it.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5052092

[WYorksWeather]

Worth just mentioning I think how remarkable (in a negative way, if you want dry weather!) recent weather patterns have been. Here is the NCEP reanalysis chart for March sea level pressure so far. We're over 10mb below the average. Absolutely ridiculous. At the centre of a giant blob of low.

Next, all of February and March combined. Still 8mb below average.

It genuinely isn't an exaggeration to say that we've been having probably the most unsettled weather in the entire Northern Hemisphere since the start of February.

And since I have a feeling someone would ask for this one if I didn't post it, here is the sea level pressure since the start of July 2023. Again, the UK and Ireland amongst the most unsettled places in the entire Northern Hemisphere.

This is why I find it hard to believe this pattern will go on much longer, having had a look at this. We can't keep on being target practice for the most unsettled conditions in the entire Northern Hemisphere. At some point, the larger scale pattern will change.

 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5052564

[Cambrian]

Hope you all had a great Easter and that the beginning of April finds you in good health.

Looking at the models over the last couple of weeks it’s easy to perceive little or no change to the pattern and no respite from low pressure for the UK and Ireland. 

However, there are slow but important changes consistently creeping in to the Northern Hemisphere profile in the longer ranges. They’ve been in recentruns of the EPS / ECM too, but here we’re looking at the 12z GEFS.

At day 5, not much change from the here and now, PV elongated in our direction, with the trough dropping down to our west, and anchored there due to an attractive bump of unseasonably warm heights along with a surface high pressure over the central Mediterranean. 

 

Another notable bump of heights up through central North America too, into Hudson Bay, maintaining the tight Bering Sea to eastern Atlantic alignment of the PV. 

By day 10, we’ve lost the heights heading up through the American Midwest into central Canada, replaced by an upper level trough, allowing the PV to fill out west, so we get low heights working down into Hudson Bay. 

 

As a result the Atlantic jet stream and trough begins to relax north, so though we still have low pressure anchored to our west, it’s further northwest and nowhere near as deep, central pressure about 20mb higher. At the same time, the loss of heights over the Mediterranean should allow easier eastern transfer of frontal systems through Northern Europe, so the setup not near as stuck. 

The same process continues through to day 16, so much indeed that the PV is now orientated Siberia to Labrador, with a fully fledged trough pointed down into eastern Canada. A good build in heights from Eastern Europe up into northern Scandinavia puts a roof over our heads so that the draught can only get in through the window.  

 

The gradual warming out of the Atlantic trough continues with the 1015mb isobar clipping the far south of the UK, high pressure relocating to the Azores, bringing the foundation for a greater chance of some more substantial ridging northeast in time, the models at least now showing signs of beginning to search out a route out of the rut towards a slow but steady improvement by, and more especially after, mid month. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5053938

[Kirkcaldy Weather]

 

On 27/03/2024 at 03:06, Kirkcaldy Weather said:

As this initial troughing clears Eastward this will open the door to colder conditions from the North during April week 1 with current trends for this to be most prominent across Northern areas of the UK.

Starting with the above, with a Lowering Isotherm there will be multiple areas of snow particularly across Scotland mostly for higher elevations though mixing occuring at lower levels will be likely, with the first seeing the ongoing rain gradually becoming increasingly wintry > snowy then as a stronger area of frontal precip comes in during April 4th and 5th with the lowest Isotherm values a snow event occurs as this moves through Scotland. 

On 27/03/2024 at 03:06, Kirkcaldy Weather said:

With further trough developments into the latter part of April week 1 in the North Atlantic this will bring an increasingly above average precipitation setup adjusting further north through Ireland and the UK.

 

On 19/03/2024 at 21:11, Kirkcaldy Weather said:

We'll begin to see an increasing influence from blocking further East which could push the Atlantic trough further west and perhaps an opportunity for a plume type setup given past experience and the time of year becoming more supportive.

During Friday and Saturday we get the first great example of the above as a cyclone begins to deepen west of Ireland with increasing high pressure across Europe to the South Southeast of the UK this gives a plume style setup with trends this will draw up highly anomalous PWAT values which indicates very heavy rainfall and a resulting flash flood risk.

This will see a large portion of Europe extending from Africa experiencing surface and upper level temperatures above - significantly above average I'd expect further temperature records potentially tied and broken.

Looking at the setup across the Northern Hemisphere by this weekend some of the most noteworthy events

• Developing Rossby Wave Break Event across America [see global thread for more info] 
• As discussed above plume setup builds across Europe
• The -NAO event connects into the + Arctic Oscillation 

With the teleconnective pairing of the move from a strong -NAO toward positive NAO values with recent stronger +AO values we'll see a focus of troughing and cyclonic developments more centering effects for Northwest and Northern UK and Ireland with a building of higher pressure having greater impacts toward southernmost UK and Europe.

This will also pair with the MJO progressing from our region of the globe ie Western Hemisphere, South America and Africa into the Indian Ocean although at a lower amplitude again feedback shows cyclonic systems trend more Northwest and Northern trackways and I would suggest further plume opportunities are plausible given feedback signal of high pressure to our East and Northeast with similar trough placements to our west and southwest most likely.

Cheers. KW ️

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5054233

[WYorksWeather]

A couple of posts tonight - firstly I want to really focus on Saturday's plume event.

The 12z GFS solution has the peak of the plume at 8am Saturday, with the 15C isotherm clipping the far SE corner, and more importantly the +12C across much of central and eastern England from the NE coast, down through parts of Yorkshire, the East Midlands, East Anglia, and the SE of England. Resulting surface temperatures peaking at 19C raw, so in practice more like 20-21C.

The 12z ECM is, as yesterday, the more extreme solution. The plume sits a little further west at 8am, and the +16C isotherm clips the south coast. This means that ECM achieves higher temperatures. We have a 21C raw temperature on the map at 2pm - hence 22-23C is a likely max in reality.

UKV is also in range now, so worth having a look at that as well. The 15z UKV again peaks the plume at 8am Saturday. We have the +15C isotherm clipping in again. Raw surface maxima reach 21C later in the afternoon, so closer to the ECM solution. UKV usually doesn't underestimate temperatures as much, so probably 22C is a good guess for the actual maximum.

Note

Worth noting yet again how unusual this plume is. At the 850hPa level, as far as I am aware (and nobody has yet posted a counterexample), a +15C isotherm even clipping the UK in early April has never happened before. In fact, forget early April, I'm not sure it has even happened in April at all!

If it were associated with surface conditions more conducive to heating (less cloud), it would likely achieve mid 20s as an absolute minimum. We would expect a temperature differential of around 10C from the 850hPa level to the surface at this time of year under fairly decent conditions. At the upper end, at a similar time of year, 25.6C was achieved on 3rd April 1946, with only around a +11C isotherm. However, this came after a much drier start to the year, and as a continuation of a longer warm spell that began in late March.

But in short, if you transplanted those surface conditions, and replaced the +11C with a +15C to +16C isotherm, something truly extraordinary could have occurred this weekend - 28-29C in early April! That is how anomalous the airmass is.

This weekend will likely pass without notice for most - the surface temperatures will be warm but unexceptional, and it may even feel a bit chilly in the presence of strong winds and little in the way of sunshine. But regardless of whether it is reflected in the surface temperatures or not, a milestone has been crossed here with such extreme warmth at 850hPa so early in the year, and multi-model agreement on its occurrence.

EDIT: Worth noting that per a further comment by LightningLover below, a +16C isotherm at this time of year (or even slightly earlier!) is not entirely without precedent. However, it is still extremely rare, and I believe still worth commenting on.

 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5054537