Model Output Discussion - Spring Has Sprung

[Rain All Night]

12 hours ago, Rain All Night said:

12z deterministic runs, out to Wed 17th Apr (day 7)

12z ensemble means, out to Thu 25th Apr (day 15)

My concise and balanced review of these charts, particularly from Friday 19th onwards, would be: YAAAAAYYY!!!

0z deterministic runs, out to Thu 18th Apr (day 7)

0z ensemble means, out to Fri 26th Apr (day 15)

It looks as though the ECM had it right in suggesting that the high will sit just to our west at first.

Later on the high currently seems more likely to be heading northwest than northeast, so we may need to rely on sunshine if we want to feel some warmth.

On 08/04/2024 at 17:59, Summer8906 said:

Is there a likelihood that the latter part of the week - Wednesday onwards - will be cloudy due to the moist nature of the airmass? Slightly concerned with one or two of the posts above (such as that of @Kirkcaldy Weather) which appear to show a frontal system passing through on Wednesday and Thursday albeit with high pressure, and mention mild and moist air - which is concerning for sunshine amounts. If so, it could be that the best weather could come through on Tuesday night!

The forecasts have been and still are showing thick cloud here today but it's brightening up considerably as I type this... hopefully this improvement will endure throughout the day...

Edited April 11 by Rain All Night

[Sun dog]

 Frigid Great to see below average rainfall. Temperature probably swayed by cooler nights. In the sun should feel pleasant (glass half full) 

[Cheshire Freeze]

GFS consistent with strong Greenland heights towards the latter part of the month-

Creates a path for the jet stream to ultimately head south once more-

Any settling down with HP close to the UK looks a temporary affair as things stand…though with the swampish nature of the landscape at the moment, any dry weather is appreciated.

Any southerly tracking low pressure will start to pack more rainfall as we approach May and more latent energy is added into the fold. That’s what made May-July 2007 so wet (high PWAT values).

Edited April 11 by Cheshire Freeze

[damianslaw]

 Cheshire Freeze These type of synoptics most likely during second half of Spring than any other time of year, and consequently not to be dismissed.

The models continue to toy with heights not gaining a full stronghold over the UK through next week, they do build enough to kill off the atlantic, but core centre is just to our west, combined with rising pressure to our NW as the core PV ebbs away, end result a chill flow from between north and east. Such developments are well outside the reliable, and heights might ridge east or south east, we haven't the heights yet though, lots of uncertainty.

 

[Metwatch]

5 hours ago, Cheshire Freeze said:

GFS consistent with strong Greenland heights towards the latter part of the month-

Creates a path for the jet stream to ultimately head south once more-

If the renewed blocking doesn't end up drifting too far west, we could end up in a cool-ish but also quite dry and sunny pattern, quite similar to April 2021 (I know @Summer8906 would appreciate that to stop the abnormally early flowering )

Tonight's GFS 12z from next weekend reminds me of April 2021 a lot.

[Scorcher]

 Metwatch That would be a nightmare for gardeners given the fact things are so advanced already- an April 2021 style spell with regular frosts would cause a lot of problems I imagine.

[Summer8906]

 Cheshire Freeze Just hope that doesn't happen, it would be quite ridiculous if we then flipped into yet another extreme wet period before the end of the month.

(Surprised the amount of rainfall would increase that much going into May compared to now, as heavy non-thundery rainfall always seems to be a late summer/autumn/early winter thing - i.e. the season when SSTs are highest).

[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 ️

[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. 

[WYorksWeather]

Quite a substantial switch around from the GFS ensemble. From next week the likely outcome now seems to be a fairly prolonged period of below average temperatures (on 1991-2020). Nothing especially notable in terms of depth of cold, though. 

At the surface, mean temperatures seem to suggest that away from prone spots night-time temperatures will be a bit too high for frosts, thankfully for gardeners. During the daytime though, the model output looks to be suggesting that we may not see 20C again this April.

Summary

All in all, after a couple of days that at least at my location felt more like early summer (shorts and t-shirt weather during the day today, probably again tomorrow), the next 7-10 days look distinctly chilly, perhaps more so by day than by night though due to the warmer than average SSTs.

At very long range right at the edges of the GFS FI we possibly see a signal for the Azores high to get going again, but it does seem like it will take a fair while to get back to anything warm, with no real signal for it at the moment after this current spell.

Personally this is not what I'd like to see (but I'm just calling it as I see it), but the one bright spot is that rain does look to be fairly scarce, so although it may well feel cold at times, this shouldn't be accompanied too frequently by strong winds and rain, except if you're unfortunate enough to live in W Scotland,  parts of N Wales, or NW England. It is good to see this after modelling in the first few days showed an absolutely shockingly wet first half of April.

The England and Wales precipitation series is already at 76% of average for the month, so it is unlikely that we'll record a drier than average month, but at least it also looks unlikely that it'll be another very wet month.

To watch

Over the next few weeks for the longer range, I'll be keeping an eye on the North Atlantic SSTs, the timing of the final stratospheric warming, and whether the current extreme temperature anomalies in the Atlantic tropical storm Main Development Region result in any earlier than usual tropical storm development for us to consider.

 

[LetItSnow!]

Perhaps my musings of a similar temperature pattern to April 1995 weren’t in vain after all as this month could very much be one of two halves. Those temperature graphs haven’t shown prolonged below normal temperatures since January or perhaps even before then! Ever the irony that it’s coming as we rapidly start to lengthen the days and spring gets going.

[Rain All Night]

12 hours ago, Rain All Night said:

0z deterministic runs, out to Thu 18th Apr (day 7)

0z ensemble means, out to Fri 26th Apr (day 15)

It looks as though the ECM had it right in suggesting that the high will sit just to our west at first.

Later on the high currently seems more likely to be heading northwest than northeast, so we may need to rely on sunshine if we want to feel some warmth.

12z deterministic runs, out to Thu 18th Apr (day 7)

High levels of model agreement at the moment. Our high won't be the biggest ever, at least not at first, but it is ever so wanted and will be ever so loved.

12z ensemble means, out to Fri 26th Apr (day 15)

After the end of the deterministic runs, the ensemble means show the high seeming to swell and migrate northwards or northwestwards.

There's no end in sight to the party by the end of day 15. 

Edited April 11 by Rain All Night

[Sherry]

Amazingly average down here in south east is 13 degrees, really goes to show how much warmer it has been! Next week 12/13 top temp, however; that’s pretty much normal 

the dry signal on the ensembles is the best part though 

[Penrith Snow]

Disappointing ECM this morning as after the northerly blast next week the Atlantic High fails to move over the UK but stays to the west of Ireland instead.

This would bring cool, cloudy conditions to much of the UK throughout next week.

GFS has more of a high pressure influence but its flabby and retrogresses in FI to give another spell of northerly winds.

After the nice day yesterday you might want to put the BBQ back in the shed for a couple of weeks.

Andy

[ANYWEATHER]

Three things stand out this morning from gfs. A drying trend nationwide,  that must be the most important thing that stands out. Secondly, a chilly airmass enveloping  the UK,  bonus plenty of sunshine, especially southeastern Britain. Thirdly,  Frost ,will be problematic for just about all nationwide.  A lot to cheer about, now the rain train is coming to a halt ,some pleasant Spring like weather on the way, ,no heavy rain , No gales , and bright cheery weather to be had , what's not to like about that! ☺

[Rain All Night]

11 hours ago, Rain All Night said:

12z deterministic runs, out to Thu 18th Apr (day 7)

High levels of model agreement at the moment. Our high won't be the biggest ever, at least not at first, but it is ever so wanted and will be ever so loved.

12z ensemble means, out to Fri 26th Apr (day 15)

After the end of the deterministic runs, the ensemble means show the high seeming to swell and migrate northwards or northwestwards.

There's no end in sight to the party by the end of day 15. 

0z deterministic runs, out to Fri 19th Apr (day 7)

Our current short spell of warmth from the south will be followed by a few westerly and then northwesterly days before the Atlantic anticyclone takes over during next week.

I wonder if there's any chance of colder air from the east making it underneath the high?

0z ensemble means, out to Sat 27th Apr (day 15)

ECM wants to keep the good times (if maybe not the warmest times) rolling right through to the last weekend of April and perhaps longer still. GEFS seems a teensy bit less sure towards the end.

Edited April 12 by Rain All Night

[Lukesluckybunch]

Gfs continuing to show..what many of us would dream of..in the winter months!we end with a lovely griceland high on the 6z..absolutely typical!

[damianslaw]

 Lukesluckybunch Yes, and very normal for second half of Spring. Indeed its rare to not see easterly or northerly episode at some stage in the spring, and they can be prolonged. 

Edited April 12 by damianslaw

[Derecho]

6 hours ago, ANYWEATHER said:

Three things stand out this morning from gfs. A drying trend nationwide,  that must be the most important thing that stands out. Secondly, a chilly airmass enveloping  the UK,  bonus plenty of sunshine, especially southeastern Britain. Thirdly,  Frost ,will be problematic for just about all nationwide.  A lot to cheer about, now the rain train is coming to a halt ,some pleasant Spring like weather on the way, ,no heavy rain , No gales , and bright cheery weather to be had , what's not to like about that! ☺

It's a much more settled outlook for sure. I just hope the high doesn't end up being further west as it'd result in something pretty showery over the east coast. The EC keeps the coldest air further east whilst the GFS briefly turns showery from the north at times but is a settled run all in all.

The AIFS is the best model as the high is a bit further east which may allow for some warmer days albeit with some larger diurnal temperature ranges.

A decent outlook overall though and pretty normal synoptics for once after the Soaking South-Westerlies (SSWs) that we've endured over recent months.

[Daniel*]

33 minutes ago, Derecho said:

The EC keeps the coldest air further east whilst the GFS briefly turns showery from the north at times but is a settled run all in all.

It’s still chilly the EPS is resolute on a spell of below average temperatures which centres on Central Europe the strongest and most persistent since January. After a record warm first half in continental Europe this is a spectacular change.

 

[sundog]

2- 3 months too late. 

 

[Frigid]

Could all go the other way but it looks like after months of above average temperatures, maybe a change is upon us. GEFS go for a pretty protracted spell of cooler weather, possible frosts where skies are clear. And with that, also quite dry conditions. Not uncommon to be seen in April.

  

12Z going for a huge Greenland block, now if only that happened a few weeks prior.. 

Edited April 12 by Frigid

[Cheshire Freeze]

Would probably see snow falling in the heavy showers with uppers circa -5

[damianslaw]

 Cheshire Freeze GFS offers the traditional winter snow cold lover synoptics in mid-late Spring, as said if you asked me when most likely date period for such synoptics, its the six week window we are about to enter, all too common.

[raz.org.rain]

"Warm days, cool nights" with high pressure currently the favoured outcome in the ECMWF outputs