Model Output Discussion - What does April have in store?

[Singularity]

A step closer when looking at the det. run middle-ground this morning; trough stalling and sliding a little west of the UK. Just needs another thousand miles adjustment west or southwest - something nearer what the 18z GFS showed (a strong match for that run is probably a bit on the optimistic side, sadly).

[Frosty.]

If you like it warm you will love the Ecm 00z, especially further s / e.. big change from the recent chill!..happy easter from the ecm!

[Frosty.]

Lovely Ecm 00z ensemble mean later this week (easter)..increasingly warm and sunny with temperatures into the low 20's celsius, the warmest spots in the s / se could hit 24/25c at the weekend..I won't go any further than that, just enjoy an early taste of summer..in april!

[Frosty.]

Looking at the Gfs 6z operational for easter, I think most would be happy with these temperatures compared to recently, Easter could easily have been a damp cool squib but instead most of it is high pressure, sunshine and unseasonable warmth.

[Tamara]

15 hours ago, Singularity said:

So now the model runs are dominated by massive retraction west of the subtropical high in the mid-range with a trough of some manner (deep or shallow) dropping in and turning things cool and unsettled for at least a few days. Really bizarre to see that with the ongoing El Nino; it's more fitting of a moderate, maybe even strong La Nina event! The ECM 12z is particularly extreme, a genuine 'what the [strong word]' run for me.

As I said earlier today, falling AAM against a +ve background often leads to overblown bursts of westerly momentum across the N. Atlantic, hence 'shove-in' of troughs across the UK.

In light of which, I'm still hopeful for a less clean and successful retraction west of the ridge, with more left across Europe and the trough grinding to a halt west of the UK rather than overhead. I've seen that manner of adjustment happen plenty of times before in the 5-10 day range.

Should that fail to occur then not only will the notion of an El Nino base state come under serious question, but the long-range modelling guidance will have landed extremely far wide of the mark yet again (for some time, they've been shouting for a notably warm 2nd half to April, which requires more than just 4 or 5 days hitting the high teens to low 20s; more like 9 or 10 - at least!).

This would further cement the idea that climate change is significantly mutating the mechanism by which the Pacific SSTs affect the global climate. So I really hope it doesn't come to that!

 

Hi James - a thoughtful summary and deserves a response

I think in the context of seasonal wavelength changes in addition to the transition period of the stratosphere to its "summer" position there is bound to be flips in patterns when wind-flow patterns undergo sequences of retractions and then forward momentum once more as we have been seeing this Spring - and is quite common to see in many Springs, notwithstanding the unprecedented changes in climate that inevitably will amplify and/or distort responses.

But the physical responses of changes in wind-flow patterns and the torque mechanisms that drive these changes remain constant nonetheless and continue to play an important role in attempting to decipher pattern changes. In that respect its another reminder that its not the ENSO base state per se that matters in terms of direct correlation, but the relationship that the atmosphere adopts to it in terms of weather pattern adjustments (in tandem with all the factors between the seasonal changes between tropical and polar stratospheres and also of course how the seasons impact sea ice at such pivotal times of switch.

What of those wind-flows?

We can see from the Hovmollers plot that since the first few days of the month we have seen a drop in a long period of westerly wind bursts across the Western Pacific towards the dateline, as part of a response to tropical convection patterns having finally weakened through March following a very long active period since November. With an imminent trade wind burst in the Eastern Pacific as can be seen shaded blue on the plot this represents a peaking of something of a "lull" phase in this Nino phase - which is not unusual in any ENSO cycle.

The effect of greater easterly trade wind inertia or reduction of Nino westerly's c/o eastward progressing tropical convection is to create a deceleration of wind-flows upstream in the Pacific and a consequential fall in angular momentum tendency

 

 Initially this serves to weaken the Jetstream heading downstream across the Atlantic, and hence has helped to promote and preserve the downstream ridge across Scandinavia, but as at the same time as the lobes of polar vortex start fragmenting in response to approach of final warming of the stratosphere, then breakaway troughs appear such as programmed next week to disrupt from Greenland to close to the west of the UK.  Meantime the downstream ridge is preserved to the east and north and east as the negatively tilted trough process gets underway as modelled.

The response of the Global Wind Oscillation, which is a plot depiction of these changes of wind-flow, is to head towards Phase 8, as reflection of falling angular momentum tendency of at least temporary loss of surfeit Nino westerly wind inertia in the global atmosphere.  This gradual orbit from the Nino phase 7 represents the first part of the jet retraction process of recent days with the blocked Scandinavian High. The second part of the process is the trough splitting the ridging pattern as the amplifying Bermuda High hoovers up our ridging to the west and allows pressure to drop in its place.

 

There are indications from the modelling that this retrogressive process c/o decelerating tropospheric and stratospheric zonal winds might complete with a further backing west of the trough and pressure rising from the SE to follow the more unsettled phase starting from the end of the Easter weekend.

 

 

This needs to be watched to see how it might unfold for the extended period in ensemble products in the next few days

 

Edited April 16, 2019 by Tamara

[knocker]

Not a bad day in these parts and temp distribution pretty much as expected

[Frosty.]

Just before the 12z runs I really liked how the 6z operational trended towards the end of april into the start of may..really pleasant / anticyclonic.

[Frosty.]

The ukmo 12h shows a change to more unsettled at T+144 hours, slightly sooner for the NW but really there's a good deal of summery weather to enjoy before then..bearing in mind that the start of the meteorological summer is still six weeks away..some of us are going to experience mid 20's celsius during the Easter weekend and widely low 20's c..eggsellent for easter and April generally!

[Methuselah]

Sunday looks like a stonker, to me:                                                                                                          

[Frosty.]

The Gfs 12z operational shows potential for 23 / 24c on sunday further s / se..can't rule out a 25c in places! Sunday becomes more unsettled across the far NW / N..fine and very warm elsewhere and then Easter Monday sees a breakdown as a band of rain spreads slowly E / SE and heavy / thundery showers break out ahead of it on what would be a warm humid day further s / e / se..lovely weather before then with high pressure and temps on Fri / Sat into the low 20's celsius..really very summery and the sun is now as strong as it is in early / mid august.

Edited April 16, 2019 by Frosty.

[Methuselah]

Wednesday might even provide what plant-life is screaming for -- torrential rain showers:

 

 

[markyo]

15 minutes ago, Ed Stone said:

Wednesday might even provide what plant-life is screaming for -- torrential rain showers:

 

 

We can pray for that to be true!

[Frosty.]

Looking at the GEFS 12z there's a chance we could again be into some very warm continental air later next week.

[Frosty.]

14 hours ago, I remember Atlantic 252 said:

 

 A real taste of summer for all of us later this week and perhaps into the start of next week further s / se...Good Friday could be unbroken sunshine across the board and for many, Saturday too. 

Edited April 17, 2019 by Polar Maritime
To move discussion on..

[MATTWOLVES 3]

13 hours ago, Ed Stone said:

 

On to the weather, things looking good, short term, a bit meh, mid term... Perhaps improving again long term! It's shaping up to be a decent summer I think.... I say decent because I don't think it will replicate 2018 or say 1976!! Something that comes to mind also... Both those summers had quite significant cold spells during the winter, and was then followed by the heatwaves.... And we had a distinct lack of any real cold spell this time.... Maybe coincidence... Maybe not!! But its a possibility! And I noticed how a fair few of the hot summers were spaced apart.... Namely.. 95....97....2001....2003......2006 

Edited April 17, 2019 by Polar Maritime
To move discussion on.

[Methuselah]

FV3 nae looking too bad at T+192: thundery rain anyone?

 

[Fourty Point Three Degrees]

1 hour ago, Ed Stone said:

Wednesday might even provide what plant-life is screaming for -- torrential rain showers:

 

 

That trough looks worrying. The kind of set up that led to the poorest cyclonic Atlantics of our weather lately eg May to August 2012, June 2016. I guess there is some real punishment to pay for our recent weather lately and very soon this dry spell will end.  Hopefully (and more likely) is that trough will detach itself and slide down across Western Europe and down into North Africa and any unsettled spell will not last long.            

[knocker]

The ecm has the front down the Irish Sea midday Monday. Regional variations with the temps Sunday/Monday

[MATTWOLVES 3]

20 minutes ago, 38.5*C said:

That trough looks worrying. The kind of set up that led to the poorest cyclonic Atlantics of our weather lately eg May to August 2012, June 2016. I guess there is some real punishment to pay for our recent weather lately and very soon this dry spell will end.  Hopefully (and more likely) is that trough will detach itself and slide down across Western Europe and down into North Africa and any unsettled spell will not last long.            

Fortunately, you can't really draw any conclusions from a trough that is featuring 8 days out has regards to it being a potential ruiner of the summer! For me the atlantic is going to be remaining in a relatively slumber mode! Perhaps low solar minimum having an affect! 

[Mike Poole]

Only skim read the thread over the last couple of days as the immediate evolution is clear, and my interest is generally where the uncertainty lies.  Longer term ECM 12z looks a plausible evolution to me.  Here out to T240:

i.e. brief unsettled blip followed by a resurgence of high pressure.  If the unsettled blip is as a result of lower AAM, then that is soon rectified according to CFS with increasing AAM from that timeframe.  

And the slower evolution through phase 6 this time could indicate a more prolonged warm settled spell than the upcoming one, but still with limited lifetime.

Further point to note, the final warming in the strat looks to be quite a dramatic capitulation, with GFS forecast straight through zero and into summer easterlies, so there's that to factor in too.

My best guess, spells of warm settled weather interspersed by unsettled spells, with the settled spells winning out and lasting longer through May.  Just ideas though...some uncertainty with all of this.

[Mike Poole]

45 minutes ago, Mattwolves said:

Fortunately, you can't really draw any conclusions from a trough that is featuring 8 days out has regards to it being a potential ruiner of the summer! For me the atlantic is going to be remaining in a relatively slumber mode! Perhaps low solar minimum having an affect! 

I agree Matt, there is no way anyone who wants a decent summer should be worried about that trough, it may get watered down (so to speak) but even if not as per above post, high pressure should bounce back afterwards. As per @Frosty. post re GEFS 12z.

[ANYWEATHER]

18 hours ago, syed2878 said:

so what has happened to all the snow you been forecasting for April I just thought I’d ask

Evening! Yes there was a Wintry outbreak across some parts of the Uk during April 4th, West Midlands and Wales got a Significant Covering....and it made news headlines!  Anyway for the outlook, Lots of Sahara dust here in todays front.... Warming up for a day or two but a short lived warm spell , by Sunday/Monday the Atlantic creeps in, I say creep because the Blocking is still in place to our northeast... But the outlook for next week looks Yuk! Wet, cold and windy depending where you are.  Perhaps ,  Some Thunderstorms  as the weather next week breaks down...

[damianslaw]

On 12/04/2019 at 20:48, Summerstorm said:

 

I can't view the charts for some reason from this time last year, but the weather looks like doing exactly what it did last year to the very day! I remember the 17th April 2018 marked a change in fortune, it was a warm sunny day, and the heat then built, peaking on Saturday 21st April, I think the first 25 degree temp of the year was hit, and for many low-mid 20s were recorded, thereafter the weather became cooler and changeable, quite uncanny how we are about to endure exact same conditions.. spooky..

A very decent start to the easter period for everyone, but fortunes change come Sunday with the NW and west coming under the influence of the atlantic, central and eastern and southern parts hold onto decent weather, before everywhere sees cooler changeable conditions by Monday. 

Next week - uncertain, much will depend on how far east the trough gets, there are signs it may disrupt over the UK with heights quickly building behind it, conversely we may see it linger in situ for a few days, fizzling out with either then a weak ridge behind before it moves in again from the NW or it builds more strongly. At any other time of year, the form horse might be for a cleaner build of heights to invade, however, the effects of the warming strat combined with the weakening of the PV, means we are most prone to fragments of the PV spinning off further trough activity from the NW aided by retraction of the azores/bermuda high, and with heights to the NE there is only one place for it to go and that is through the UK.

[I remember Atlantic 252]

1 minute ago, ANYWEATHER said:

Evening! Yes there was a Wintry outbreak across some parts of the Uk during April 4th, West Midlands and Wales got a Significant Covering....and it made news headlines!  Anyway for the outlook, Lots of Sahara dust here in todays front.... Warming up for a day or two but a short lived warm spell , by Sunday/Monday the Atlantic creeps in, I say creep because the Blocking is still in place to our northeast... But the outlook for next week looks Yuk! Wet, cold and windy depending where you are.  Perhaps ,  Some Thunderstorms  as the weather next week breaks down...

As usual this location didn't see a flake on April 4th, while other areas got loads

[Frosty.]

I don't remember a wintry outbreak..I must have been asleep for the last week!

Anyway, lovely warmth and sunshine incoming and then next week looks cyclonic with sunshine and heavy showers with a risk of thunder and I noticed some decent uppers next week on the Ecm 12z so it could be warm in the sunshine and possibly feel a bit humid. Longer term the GEFS 12z hints at some very warm continental potential at the end of april and into early may.

T+240 Ecm 12z not bad either, high pressure to the west and east putting the squeeze on the UK trough as it drifts away to the south so a filling departing trough and high pressure taking control again beyond day 10 looks the most likely outcome based on this chart.

Edited April 16, 2019 by Frosty.