Model discussion highlights

[Kirkcaldy Weather]

On 03/04/2024 at 22:05, Kirkcaldy Weather said:

There is likely to be further cyclonic development during the beginning of next week with a dip in the upper level dynamics however discrepancies on the track with some indicating the Bay of Biscay wheras others pull it into this weekends cyclonic developments with movements toward the UK.

As this cyclonic system develops and crosses the UK there are a multitude of developing dynamics.

• Sharp Thermal Gradient.
• Significant flash flood risk with a significant rainfall event.

As this system continues to develop and undergo cyclogenisis as it crosses the UK there will be a sharp thermal gradient occuring on its northern and particularly Northwestern flanks, this combination will aid in the formation of a significant rainfall event with an associated significant flash flood risk, a few discrepancies on precise track between the models however South and Southeast Ireland, West and Northwest Wales, particular focus into Northwest England, and Scotland.

As the sharp thermal gradient continues to intensify this will turn the rain to snow particularly across higher routes however mixing at low levels can't be ruled out, I expect main accumulations at this stage to be across the Pennines and Scottish Highlands.

These below average temperatures will lead to a cold night on Tuesday with a frost a possibility.

Into midweek the PWAT values once again become highly anomalous, wouldn't surprise me if records are broken at upper levels of the atmosphere for moisture.

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.

Similar to Kathleen/Olivia this moisture inflow is tropically sourced. 

We'll return into an above average temperature setup with this systems influence.

 

On 02/04/2024 at 21:04, Kirkcaldy Weather said:

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.

All fitting in ideally with expectations this is an excellent teleconnective configuration for significantly cold air to be entreched across the Arctic I expect helping the Arctic Ice too @Midlands Ice Age 

Heading toward Mid April I'm watching for a plunge of Arctic air as troughing develops to the North of the UK and moves toward Scandinavia and Europe bringing a flow from the Northwest and North.

Thanks for Reading. 

KW

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5055864

[johnholmes]

The 6-10 day 500 mb anomaly chart from NOAA shows a fairly marked Confluent ridge leading into a Diffluent trough off the coast of n America. This can lead to the development of a surface low, possibly rapid deepening. So at some stage in this time scale we could expect a fairly deep surface low to form in that area. The flow is then shown as SW'ly fairly strong at 500 mb. So a rather unsettled outlook in the 6-10 day period seems quite likely

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5052951

[danm]

No comment on the models this morning? 

In a nutshell, we have a nasty little feature tomorrow that'll give many of us cool, windy and damp weather. After that, pressure builds to the south and SE, bringing sunshine and temperatures up to 20c across these areas by Thursday and through the weekend. 

The ECM then makes more of that NW'erly blast, bring cooler temperatures again by early next week, but the GFS doesn't make too much of that and quickly rebuilds pressure from the west, settling things down nicely. The UKMO only goes out until next Sunday, but looks similar to the GFS in that it looks a lot less primed for a NW'erly in the way that the ECM shows. 

Step by step, this is what each run shows for tomorrow:

 

Then later this week with the build of pressure to the south and south east:

 

 

 

Then towards early next week, here's how each of them deal with the chillier NW'erly:

ECM:

 

UKMO only goes out to Sunday:

 

GFS - keeps any NW'erly very brief, with a quick rebuild of high pressure:

 

 

What about the means:

Less bothered about 850's at this stage, so looking at pressure, the GEFS has a short dip before pressure builds again by the middle of next week - graph is for London:

 

...and for Manchester:

 

The ECM mean unfortunately is less keen on a quick rebuild of high pressure and keeps any rebuild fairly weak:

 

So we can confidently say that tomorrow looks awful for many, then much warmer, sunnier and drier across the south/SE midweek onwards and into the weekend, less so further north and west, then uncertainty over the potency and longevity of the NW'erly and how quickly and to what extent high pressure rebuilds into next week. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5055995

[Cambrian]

Looking at the next ten days, which cover the middle third of April, t’s good to see the relevant part of the annual cycle, in the form of the springtime waning of the PV, well underway. 

It is happening a bit later than the last couple of years, but is striking nonetheless, here on both the 0z ECM operational run and ensemble mean, day 1 - 10 animations, the PV very much on the wane, being nibbled away by evolving mid-latitude ridges, with the core PV diminished and returning from the Siberian Arctic to the pole. 

 

This leaves us with a solidly meridional 5-wave hemispheric pattern by day 10, shown nicely on the op and mean anomalies, ridges by then through western North America, up through the eastern seaboard, Western Europe, Kazakhstan up into Siberia, and the far east of Russia. 

 

The picture for the UK and Ireland alternates from seeing a shallow ridge over the next few days, to being under the influence of an active low pressure system passing through with the trough around days 5-6, before the arrival of a better amplified ridge by day 9-10 as the more meridional pattern firms up.

Day 10 provides a convenient juncture for the UK and Ireland for showing the potential for something more settled getting a bit further north to be more widely shared, op and mean again.

 

However, it looks very much like it’s a snapshot in a slow but steady revolution of the 5-wave ridge / trough pattern around the pole, with approximately 4 days appearing to be the current phase for the ridge to trough transition, hinting at a period of drier, brighter spells of 3-4 days alternating with more changeable spells of 3-4 days.

A much more normal and much more pleasant a pattern on view as spring more clearly shows its hand. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5056678

[Kirkcaldy Weather]

Tonnes of fascinating evolutions occuring teleconnectively

I'll start by revisiting the Arctic Oscillation which I discussed here

On 02/04/2024 at 21:04, Kirkcaldy Weather said:

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.

Taking the data from the above post 

Easy to see the -AO event has become even stronger than anticipated, the strongest positive values for a long time and stronger than during the whole entire winter season.

On 07/04/2024 at 19:34, Kirkcaldy Weather said:

All fitting in ideally with expectations this is an excellent teleconnective configuration for significantly cold air to be entreched across the Arctic I expect helping the Arctic Ice too

We can watch as the extremely cold airmass associated with the Tropospheric Vortex begins to move from the Russian end of the Arctic across toward the Alaskan and Canadian end. Values at -28C 850hpa ongoing possibly some nearing -30C and still maintaining at least -24C at 850hpa upon the position shift.

On 07/04/2024 at 19:34, Kirkcaldy Weather said:

Heading toward Mid April I'm watching for a plunge of Arctic air as troughing develops to the North of the UK and moves toward Scandinavia and Europe bringing a flow from the Northwest and North.

This can be noted from the above animations but delving slightly deeper.

Trends show the coldest conditions becoming centred across Europe.

Very fascinating setup hemispherically we've got a number of Rossby Wave Break Events.

I have already discussed most of these and some of their impacts here

 

 

Focusing on the North Pacific this looks the most impressive and set to continue development into an ongoing Rossby Wave Train - RWT

We also have a developing Rossby Wave Break Event from the North Atlantic through Europe and North Africa by Mid April 14th > 15th.

The right hand cut off low will be part of the significant cold temperatures across North Africa as discussed in my post in the global temperature thread however this will also bring a significant flash flood risk as a significant rainfall event occurs in Tunisia extending into Northeast and North Algeria.

To fully understand the upcoming developments beyond this timeframe we need to look in detail at recent and ongoing teleconnective developments.

To do this I'd like to revisit my posts from the start of January, January 20th and March 4th.

 

 

 

Beginning with the MJO and El Ninò, a lower amplitude cycle was always going to occur and upon doing research this is a common occurence during the latter stages of strong/super El Ninò Events with the following excerpts from 

"The eastward propagation of MJO was also observed during the decaying stages of the three super El Niño events, but its intensity was weaker compared with the developing and mature stages."

"3.3 Decaying stages

The eastward propagation of the MJO could be observed during the decaying stages of the three super El Niño, but their intensity, duration and propagation distance were significantly weakened compared with those in the developing and mature stages (Figure 2). The spatiotemporal spectral analysis in Figure 3 also showed that power spectrum of intraseasonal eastward propagation during the decaying stages of the 1997/98 and 2015/16 El Niño events were relatively stronger than those during the 1982/83 El Niño. The central periods of the eastward propagation for the MJO were mainly 40 days and 75 days during the decaying stages of 1997/98 El Niño, and it was primarily 40 days for the 2015/16 El Niño. However, there is no center of intraseasonal eastward propagation during the 1982/83 El Niño. The strong wave of eastward and westward propagation of lager than 90 days appeared in the decaying stages of the 1982/83 and 1997/98 El Niño events, which may be induced by the conversion of the MJO energy to low-frequency energy of above 90 days (Li and Zhou, 1994; Li and Li, 1995). At the same time, the high-frequency wave activities of the eastward propagation were prominent at 20–30 days during the decaying stages of the 1997/98 El Niño. In addition, the eastward propagation center of zonal wave 2 was detected during the decaying stages of the 1982/83 El Niño.

The evolution and composite results of the RMM index during decaying stages of three super El Niño illustrated that the MJO activity in the decaying stages is significantly weaker than that in the developing and mature stages. The MJO intensity in the decaying stages was the weakest, especially for the 1982/83 and 1997/98 El Niño events (Figure 2; Figure 4; Figure 5). The RMM indexes of phase 4–8 during the decaying stages of the 1997/98 and 2015/16 El Niño changed from positive anomaly in the mature stages to negative anomalies, particularly in phase 6–8 (Figure 5C). The strong MJO activity led to the increase in the average RMM index of phase 4-5 in May 1998. The two robust MJO activities in June and July 2016 also enhanced the average RMM index of phase 1-2 during the decaying stages of the 2015/16 El Niño. Many studies had indicated that the robust MJO activity in May 1998 triggered the easterly anomalies, resulting in the termination of El Niño. After the MJO event, the Niño 3.4 index rapidly decayed from positive anomaly to negative anomaly (Takayabu et al., 1999; Miyakawa et al., 2017). Figure 2 showed that during the decaying stages of three super El Niño, when Niño 3.4 index turned from positive to negative, the MJO easterly existed in the eastern Pacific, which demonstrated that the MJO easterlies may accelerate the extinction of strong El Niño. Meanwhile, the MJO westerlies in April 1998 and June 2016 existed in the eastern Pacific, while the decaying rate of the Niño 3.4 index was prominently reduced. The anomalous MJO zonal wind amplitudes in the Indian Ocean and Pacific were weakened in the decaying stages, especially in the 1982/83 and 1997/98 El Niño, while they were enhanced in the central and eastern Pacific, particularly in the 2015/16 (Figure 6). The MJO zonal wind amplitudes strengthened over the eastern Pacific, which may lead to the stronger 2015/16 El Niño. These results indicate that the MJO plays a critical role in the decaying stages of El Niño while it is necessary to further study the interaction between the MJO and the decaying stages of El Niño."

Taking the MJO progression of late we see this evolution occuring again with the lowest amplitude involved with progression across the Indian Ocean.

There are many areas of importance and interest here.

With ongoing discrepancies between all models on amplitude and progression / timing of this cycle its no surprise seeing associated differences within the outputs which will continue until this is worked out however there are patterns which are increasingly probable given recent progression and continuing feedback of El Ninò which I will discuss below.

As I discussed in my posts during January it's not overly shocking seeing the MJO decreasing in amplitude across the Indian Ocean given interesting recent developments involving the Indian Ocean Dipole.

Taking the data from my post in January the IOD looked to weaken markedly and be at neutral - potentially negative by this current timeframe.

Met Office 

BOM

This weakening close to neutral has occured but a re-emergence into positive IOD conditions are occuring a bit earlier and stronger than those outlooks.

Newest Data courtesy of Met Office and BOM

 

Other seasonal models also trending into more of a noticeable +IOD

 

 

Looking at upcoming developments and revisiting my post from October

 

"I've enjoyed researching the PNA further extending more information than the bits I knew already and having found multiple papers there's a clear connection with the PNA and upstream blocks either Scandi Greenland or a mix of both which stems from Rossby Wave Breaking in most scenarios as we are and have witnessed lately."

We are seeing the most negative PNA since Late February.

Pairing this with the MJO in the Indian Ocean and the Maritimes in April in an El Ninò plus feedback typically seen in association with El Ninò

From now through Mid April we see the Atlantic Ridge regime which could extend across Ireland possibly the UK for a time, with this transitioning into blocking to our Northeast, North and most likely Greenland too.

As shown in my post from October and other occasions a negative PNA can lead to a cold - potentially significantly cold temperature anomaly from the Northeast-East

Recent GFS outputs.

Thanks for reading, KW ️

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5057116

[Cambrian]

Blimey. Outstanding choreography from the ridge dance troupe, lining up to really sock it to the PV on the NH dance floor over the next 10 days on the 12z ECM operational run. Let’s watch the elaborate performance as successive waves of heights push north.

Starting from where we are today, PV centre stage, coordinating Atlantic, Scrussian and Bering Sea troughs in a whole hemisphere twirl.

 

Keep an eye on that little pocket of heights over the Canadian seaboard with the hook north, because….

 

…first up is the Atlantic ridge by day 3, still with the northward extension of heights, now extending well up through Baffin. 

By day 5, the PV still holding centre stage, but the Atlantic ridge has been joined by the Alaska ridge, a sweet little link-up of heights pushing the lower heights east. But about to join in is a nascent ridge pushing up the east of Japan towards eastern Russia, and there are hints of a naughty little squeeze from Kazakhstan. 

 

By day 9 / 10, the Kazakh squeeze is maintained, well and truly heating up that floor, while the Japan surge goes all-out Siberian, joining their friends from the west in a hemispheric Cha Cha that ultimately congas its way right through the heart of the Arctic. 

  

PV exit stage left, arrivederci.  A good few days respite for the UK and Ireland.

Yeah, sign up everyone (if you’re not totally exhausted), the moves are awesome. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5057123

[Mike Poole]

After a pretty torrid couple of months, the pieces are starting to move towards something much more palatable.  It is no surprise that this is happening now, as the effects of the significant zonal wind reversal in the strat at the end of February start to wane.  

The NAM index over the last couple of months looks telling:

This is effectively the Arctic Oscillation (AO) but at all layers of the atmosphere, and you can see from the plot how the negative values from the SSW have continued to just sit above the troposphere and impinge our weather ever since.  That doesn’t mean we’ve had constant easterlies here - not all SSWs result in this anyway for the UK locally (and I think the ones that do are becoming rarer, I’ll come back to this), but the effect on the northern hemisphere more generally has been marked.  

The plot also shows that into the forecast period, that reign of terror from the strat is now over it has fully downwelled - it is benign from now on, so normal spring patterns have a belated chance to take hold.

A final comment re the strat, and how things may be changing with global warming.  With only 6 SSWs historically per decade, it is perhaps too early to tell, but my intuition is, well, two things, a) that SSWs are becoming more frequent, and b) that, when they occur, they are becoming less likely (than the 66% rule of thumb) to deliver cold scenarios for the UK in winter.  

A much more settled outlook is starting to become apparent in the 8-15 day modelling, here’s the ECM clusters T192-T240:

Clusters 1 and 2 (combined with 44/51 of the runs) showing high pressure in charge over the UK, how welcome is that!

T264+:

Clusters 2,3,4 show a continuation of the high pressure local to the UK, but the main theme from all the clusters is the lack of anything from the Atlantic, finally, with the other clusters generally having a ridge to the west of the UK, which would be a cooler scenario.  

 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5057333

[Kirkcaldy Weather]

On 07/04/2024 at 19:34, Kirkcaldy Weather said:

Heading toward Mid April I'm watching for a plunge of Arctic air as troughing develops to the North of the UK and moves toward Scandinavia and Europe bringing a flow from the Northwest and North.

Active period of weather with this.

Number of dynamics going on, we have a cold front which will be finishing its journey through Ireland and the UK by midday Monday.

With a strengthening Jet Streak interacting with the cold front there are a few heightened threats these being increased wind gusts with trends for embedded potentially damaging gusts and also a potential for tornadic activities embedded along the cold front I'd suggest parts of Ireland and also Wales and Southwest England being particularly at risk though it's a wide area overall.

To the Northeast of this active Jet Streak we have a deep cold pool moving in at 500hpa, this corresponding brilliantly with a pool of increased instability meaning the showers having a higher expectation of being thundery in nature and combining to the Lowering Isothermic values a wintry mix with snow mostly at high levels though not exclusively with hail and sleet to lower levels. Northwest, North and Northeast England and Scotland seeing the most of this activity.

As this Arctic plunge descends through Europe this brings yet another significant snowfall event across the Alps, a very repetitive and common occurence during this El Ninò. I'm also noticing the signal of a significant snow event in Bosnia and Herzegovina from Wednesday through Friday.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5057797

[Cambrian]

Shiver me timbers! 

Looks like we have a retrogressing high before our very eyes, ha ha haar (and other pirate noises) - even before it’s properly arrived.

Whether ‘twill be as shivery as 6z GFS op at day 9, where it withdraws far enough to the northwest to allow a proper cold blast down the frontage with some snow a fair way south, and settling on the hills…

   

or holds close enough nearby to keep the old lunger a bit further east like on the 0z GEM op at day 10 (beware that sea serpent beyond the pole, haar)…

the retrogression and European trough are definitely looking to be features of week 2 - ‘tis here too on the 0z EPS at day 11. Aar.

The CFS weeklies (weeks 1-3) show the Euro trough by week 3 being reinforced by its maritime buddy that’s come romping through the Azores in weeks 1 and 2, while to the north, the Atlantic heights hint at wobbling back east, a tad back our way again…

  

…the big concern for us island landlubbers looking for something to warm our jellies is that rather than a generally quiet but cool outlook, the pattern in the event all heads just that bit further north bringing us back into chilly cyclonic influences that just judder your rafters. More pirate noises….

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5057987

[WYorksWeather]

In relation to the previous discussions around the final warming, here is a paper I found recently which discusses this in much more detail. I've summarised a few points below on my reading of it, but I definitely welcome any input from the various pro meteorologists and other experts we have on this forum in case of any misinterpretations on my part.

Skilful predictions of the Summer North Atlantic Oscillation

WWW.NATURE.COM

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The Summer North Atlantic Oscillation responds sensitively to an anomalous strength of the stratospheric polar vortex in spring, which can be exploited for seasonal predictions, according to large-ensemble...

Details

From my reading of this, the proposed mechanism for a late final warming leading to better prospects for summer (particularly early to mid summer, so June and July) is as follows:

1. A later final warming typically means a stronger than average polar vortex in May at 10hPa
2. This means that at lower stratospheric levels like 50hPa, the polar vortex can persist into late May or even into June
3. This tends to then correlate with a positive phase of the Summer North Atlantic Oscillation (SNAO)
4. A +SNAO correlates with drier and warmer weather for the UK in summer

There is also an additional factoid - a late winter SSW (defined as occurring between 1st February and 15th March, that is not the final warming) correlates quite strongly with the strength of the polar vortex in May, and therefore have a sizable impact as well on the causal chain above.

There is a significant amount of experimentation in the paper that does seem to support the idea that this is causative, not merely a correlation. In years where the vortex at 50hPa in May varies by 1 m/s or more from climatology, the relationship is particularly strong, with a correlation of 0.55 (which if you know your stats means it explains 0.55 ^ 2 = 30% of the variance in the summer NAO, which is quite a lot).

This is of course pretty cutting edge, with the paper only being published in November, but it does seem to make sense.

Summary

So, the upshot for our summer is that we have very positive signs if you're looking for a warm and dry one:

• A late winter SSW promoting a positive May Polar Vortex Index (MPVI, which the paper defines as a stronger than normal vortex)
• If we do get a positive MPVI (as most forecasts of the polar vortex are suggesting), then this correlates, (and may in fact have a hand in causing) a positive summer NAO
• A positive summer NAO correlates with a warm and dry summer for the UK

This is not of course, definitive. No one factor can guarantee a warm and dry summer. But having any predictability is still an improvement - previously prediction of the summer NAO was considered to be essentially impossible even at very short lead time, unlike the winter NAO.

In any case, I hope this fairly deep dive into the final warming and its impacts is useful, and if you are interested the paper is linked.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5058129

[Cambrian]

This appears to be quite a telling moment in the development of this spring. The Atlantic jet stream is heading very decisively north before fragmenting, here on the 0z ECM op for the next 10 days.

The 0z ECM mean anomaly shows an impressive build in heights not only north through the Atlantic but also west into Greenland. The low pressure over the pole is lost as heights link up through the Arctic to the Siberian side. So the pattern is getting locked down.

 

From the meridional 5-wave hemispheric pattern we’ve been looking at recently, we might have seen the next stage involving injection of some energy to incorporate a couple more waves, reduce the amplification and introduce a more mobile setup, but instead we’re seeing the opposite happen - the Atlantic build is so substantial that it serves to carve out one of the waves altogether. 

This is shown nicely by the 0z GEFS jet stream charts, the 5-wave starfish at day 5 being replaced by a 4-wave cross at day 10, the jet stream actually bending back on itself with a northeasterly component as it dives south towards the UK and Ireland. 

 

The surface flow will be very much in the northeast for several days, following the contour lines in the mean heights charts (below) from around day 5 onwards. 

So we’re moving towards a more static setup towards the end of the month, drier than it has been, but with suppressed temperatures. The stronger sunshine when on offer could make for some pleasant weather all the same, especially further west with shelter, though as discussed, the onshore breeze could be quite the dampener in eastern parts at times. 

 

One more thing, looking through to day 10, the upper trough remains uncomfortably close by to the east, even steadily working its way further west - so small systems beginning to run down the western flank of the trough, picking up moisture through the Norwegian Sea, might well become an added complication later on next week. 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5058638

[Kirkcaldy Weather]

On 29/01/2024 at 14:25, Kirkcaldy Weather said:

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.

Want to start by revisiting the above statement from January, there can often be discrepancies between the various Meteorological Agencies particularly regarding ENSO statuses but we have BOM first to declare ENSO Neutral. 

 

Per my recent post here 

 

I discussed that the Super El Ninò Event had transitioned into more of a West Based Event, the latest ENSO discussion from NOAA agrees and gives further info 

https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

We'll have to await JMA and NOAA anouncing ENSO Neutral conditions and personally I dont get involved in debates a la Twitter last year with many arguing we weren't in an El Ninò though as I have discussed prior no 2 ENSO events behave indentically though there are common characteristics of each ENSO, and there can be lag in the Oceanic > Atmospheric 'coupling'.

Newest ENSO outlooks from Met Office suggest ENSO Neutral heading into May with the oncoming La Nina conditions intensifying in the 1 & 2 Regions quite fast.

Starting to see more details to add to some of my recent posts.

On 11/04/2024 at 20:28, Kirkcaldy Weather said:

We can watch as the extremely cold airmass associated with the Tropospheric Vortex begins to move from the Russian end of the Arctic across toward the Alaskan and Canadian end. Values at -28C 850hpa ongoing possibly some nearing -30C and still maintaining at least -24C at 850hpa upon the position shift.

On 11/04/2024 at 20:28, Kirkcaldy Weather said:

Trends show the coldest conditions becoming centred across Europe.

On 11/04/2024 at 20:28, Kirkcaldy Weather said:

From now through Mid April we see the Atlantic Ridge regime which could extend across Ireland possibly the UK for a time, with this transitioning into blocking to our Northeast, North and most likely Greenland too.

Looking in more detail, the most significant developments upcoming, as the cyclonic system discussed here

 

Merges with a cut off low in Northwest America this will link to the Tropospheric Vortex which is modelled to greatly intensify with indication potentially record breaking low pressure into Canada. 

Part of the MJO Indian Ocean > Maritimes feedback in an El Ninò in April as posted prior 

As shown in my recent post we continue to see the Atlantic Ridge in an El Ninò setup with another cold plunge during the next few days.

Following on we have the high pressure moving into Ireland and the UK as mentioned prior plus as the Tropospheric Vortex developments occur in Canada this paired to the Negative PNA will see a high descending from West Canada across America with a new Arctic air outbreak, a relatively common pattern of the last few months which I've covered in the global thread. This will bring significantly below average temperatures.

On 11/04/2024 at 20:28, Kirkcaldy Weather said:

As shown in my post from October and other occasions a negative PNA can lead to a cold - potentially significantly cold temperature anomaly from the Northeast-East

During the latter stage of April week 3 through April week 4 the Atlantic and Ireland-UK high will begin to take on the MJO and PNA feedback of blocking to our Northeast > Scandinavia and Russia, this will also retrograde into Iceland and Greenland as discussed prior with a good representation of many of the major European weather regimes / teleconnective feedback.

 

Euro-Atlantic weather Regimes in the PRIMAVERA coupled climate simulations: impact of resolution and mean state biases on model performance

LINK.SPRINGER.COM

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Recently, much attention has been devoted to better understand the internal modes of variability of the climate system. This is particularly important in mid-latitude regions like...

Nothing surprising here factoring in recent MJO progression with an ongoing probable further feedback of multiple Stratospheric > Sudden Stratospheric Warming Events, *though the current zonal winds are above average.

Overall a prolonged period with below average temperatures will continue with some significant anomalies across Europe in particular, we then look during April week 4 as the High retrograde gets going for these below average conditions to extend into the UK > Ireland.

Thanks for reading. KW

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5058911

[Cambrian]

Little point ducking the issue. A quacking weekend in store…

 

0z ECM op for day 4, as another low pressure system finds us with impressive timing!

Further ahead, some more positive signs - once we start seeing this type of “super-meridional” pattern - ambitious building of heights up through the Atlantic and more spectacularly, through all the S’s - Sahara-Sweden-Svalbard-Siberia-Seguam like here at day 6 on the 0z ECM op…

 

…it’s only a matter of time before we start seeing the trough becoming over-extended with the cutting off of the low at the base of the trough, it sinking south, the heights linking up through the UK and Ireland like here at day 8…

 

Yes, add Skegness and Sandymount to your list, spectacular super-meridional S thing!

After that, a weaker version of the trough tries to reassert itself from the northwest, which the GFS op has been keenest on, though looking at the 0z ensemble mean, the pressure never really falls away again, a steady rise to a respectable 1020mb for Birmingham by the end of week 2…

…which is consistent with the ECM charts and the pincer movement of heights weakening the polar trough at its stem - so though nothing wall to wall by any means, the chance of a somewhat more promising setup emerging into early May.  I’ll post again around then. All the best.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5060751

[WYorksWeather]

Tonight we seem to not have a great outlook in the short to medium term.

After we get the current cool cyclonic period out of the way over the weekend (unfortunately a pretty dreadful one for most), into early next week we have a warmer pattern developing for Tuesday and Wednesday, but nothing particularly impressive. Raw maxes of 17C on Tuesday and 20C on Wednesday, perhaps in practice 18-19C and 21-22C. Exact figures probably dependent on timing of cloud and rain.

Wednesday possibly a new warmest day of the year, but nothing out of the ordinary for the start of May. 

 

However, further into May we have a significant pattern change on the GFS tonight. In the extended range, the 12z at around day 12-14 sets up a high over and to the east of the UK. It's not the strongest, but especially eastern areas you would think stay mostly dry under that.

The temperatures are nothing spectacular to be fair as the core of the resulting heat plume is away to our south, but a number of days with very pleasant afternoon temperatures in a row.

Of course, this is a long way off.

In terms of the ensembles, the GFS still isn't that interested, but it has mostly erased the cooldown after the initial warmup around the middle of next week, and a bit of a signal to follow the GFS OP later on to a lesser extent, so I guess already an improvement on what was showing 2-3 days ago.

Summary

Still a long way from any sort of heatwave or anything particularly notable, but the pattern on the GFS 12z OP would be pleasant enough. Certainly a welcome improvement.

From a personal perspective, I'll be paying close attention to forecasts for May Day and the following week (commencing 6th) as I've booked it off work.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5061632

[WYorksWeather]

Bit of a late night update - did the ECM 12z follow the GFS 12z with a warmer spell in FI? The control (OP doesn't run far enough) says no - the whole pattern is a few hundred miles to the west, and we're actually stuck under cool and cyclonic northerlies.

To be fair, the control was amongst the coldest runs. One pattern that we do notice though is that the downward trend in temperatures after the warmup early next week has been downgraded to more of a return to average, similar to the GFS 12z ensemble. Still no sign of anything particularly warm though on the mean, but still looks a fair bit warmer than of late overall.

Next is the GFS 18z. Ensemble isn't out and I'm not waiting up for it, but does it follow the 12z?

The answer, much as with the ECM, is no. The pattern is not as far west as the ECM, but the high is over and to the south of the UK, which is badly positioned for any real warmth. Nothing overly cold, and should be largely dry, but I'd hesitate to call it warm.

All in all, not the most inspiring late night update after the earlier optimism. I imagine the models will still go back and forth a bit around May Day and beyond as we still have a fair way to go.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5061787

[WYorksWeather]

The GFS 00z ensemble has now fully eliminated the cooldown in the mean - temperatures now looking consistently near or above average.

Looking at precipitation it seems like we'll struggle to keep things entirely dry though - a fair few precipitation spikes. But certainly nothing there screaming extremely wet pattern - the mean rainfall is pretty low which suggests it'll be dominated by infrequent showers rather than heavy frontal rainfall.

 

Sea level pressure tells the same story as well - mostly on the rise after this weekend's dip.

All in all - not too bad. It's also interesting how the number of warm outlier runs is beginning to increase again - an odd run taking the temperatures above 25C, like P20 of the GFS, with a broad area of high pressure over the UK and centred to our south east.

Also looking at the dam lines a very strong high for the time of year - the 584 line into the SE of the UK.

By the end of the run some very hot air just to our south as well, so the pattern may have continued beyond the end of the run.

The first heatwave run of the year - taking into account a usual under-read of 1C or so many areas would surpass the Met Office heatwave thresholds with this.

Again, only one option and a very long way away, highly unlikely to verify. But as many of us have been saying we need to be on the lookout for these very warm outliers and see whether they gather any further ensemble support. Most of the time they do fall away again but sometimes they keep gathering momentum...

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5061824

[johnholmes]

A look at the 500 mb predictions

THREE weeks since last did in depth check!!

Sunday 28 April

NOAA first then ECMWF

Well at long last little signal for Upper ridging CLOSE to the UK but still very much in evidence in polar regions. Small +ve showing where the major winter trough usually resides (ne Canada/sw Greenland. Very slack flow into the far northern UK from s of west whilst almost nil for the major part of the UK. Main signal for contour troughing is around 40W and 40 N; (the remains of the major winter troughing perhaps?). By the 8-14 and the chart, to me, shows what we should expect for mid spring from the far west across into Europe? A very small +ve anomaly showing over nw Iberia.

Turning to the ECMWF output for much the same 6-10 day NOAA set of charts, actually 4-8 May,

It starts with the ridge just ne of Scotland extending sw with troughing still showing over ne Europe. During the period the 500 flow becomes a more general westerly over the approaches and the UK itself into Europe with the trough moving east with it showing north of the Black Sea and Turkey by the 8th May.

So pretty similar really to the flow at 500 shown on the NOAA outputs. Not exact of course but one could say about on the same pages!

As they are fairly similar, and from occasional peeps over the last few days, the pattern seems to have evolved fairly sequentially, I would imagine the upper flow will not be too different in the 6-10 period and beyond.

This is likely to see, at least, a decrease in what seems like the UK’s own monsoon season for many to a, not completely, but drier interval. Also with some local variations (sorry East coast effects at times), somewhat more seasonal temperature values than the late January sample many have had recently. As to any specifics then possibly still more ppn for southern parts at times but I feel the ppn will be more likely to affect other areas also. Whether thundery developments develop is beyond this brief peer into what may happen.

Good luck, sometimes this use of 500 MB flows does give a good idea of the next 2 weeks at that height but minor day to day variations can and do play havoc with attempts at predicting what the bottom 18,000 ft of the atmosphere can turn up!

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-spring-has-sprung/?do=findComment&comment=5062362