Model Output Discussion - May and Early Summer!

[Tamara]

Extracts posted last week on closed thread:

 

The other part of the equation is the seasonal transition within the stratosphere from its winter default vortex position to its summer state. This is bound to increase -ve momentum (easterly) zonal wind activity across the pole and manifest blocking tendencies at high latitude which adds further to NWP vicissitude...…..

...….Mitigation of HLB sustaining too long also probably aided by a weak El Nino forcing which acts to help the ITCZ further north in late Spring heading into early summer sooner than under low angular momentum La Nina conditions......

Forthcoming prospects?

….. assuming active tropical >extra tropical forcing sustaining angular momentum tendency through the greater part of May c/o weak El Nino circulation and aligned with w/QBO, increasingly inhibiting Atlantic and Greenland blocking heading towards the important seasonal wavelength setting as Spring turns towards Summer, then whilst such a pattern will inevitably sustain backwards and then forwards once more-  its not unreasonable to hypothesise further re-setting of the Atlantic trough and downstream W/European ridge and re-cycling of increasingly warm patterns from an ever warming continent as the days keep growing longer.

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The most recent post following these extracts spoke of fine margins in respect of much of the wider discussions ongoing in these summaries.  

Categoric underestimation in that analysis, no doubt, of the vast amounts of vertical heat transfer generated into the pole by the recent Scandinavian height anomaly -

 

- which has further augmented the final warming and thus created the "dynamic" response to the final seasonal warming of the stratosphere that has made the difference between a more conducive Branstator (mid latitude) ridging arrangement to late Spring warmth and the highly anomalous Greenland block verifying instead. The result being the polar vortex splitting and leaving a core cold element to our NE which is set to spoil the B/H weekend temperatures and increasingly also looking set to usher in a southerly tracking procession of lows from midweek.

So one might assume such a reverse polarity outcome has also scrambled the polarity of the whole analysis, and left credible extrapolations of cool cyclonic conditions for weeks on end in its legacy instead?   No, not really.

The fundamentals remain that the seasonal stratosphere/troposphere transition might well be simply masking the direction of travel to an ultimate destination that sees transport of the end of season cold vortex back across the pole c/o the reverse polarity, helping to converge a mid term cyclonic mess in the process right over our heads, but with the Greenland height anomaly also fading and backing west towards Newfoundland and Canada with the result that something of a west based -NAO allows pressure to rise from the south and starts to draw up warmer air in the process.

There are some hints of this in extended means, albeit the exact timing of this is open to question circa a few days bandwidth.

Such an evolution would go full circle to re-setting the original analysis suggesting of an Atlantic trough and downstream ridge and return of something much more seasonal.

As depicted by the sharply defined edged red anomaly in the Hovmollers plot below, this pattern evolution also draws on the significant westerly wind burst about to be set in motion in the West Pacific as the strong tropical CCKW related MJO wave propagates further east (and ultimately engages the standing wave at the Pacific dateline) -

 

-and hopefully keeps a borderline Nino signal going into the start of summer and which assists in choreographing a rossby wave pattern suitable for downstream mid latitude ridge building (as the wildcard -ve easterly anomalies at higher latitudes fade out to summer transition of the stratosphere/troposphere state)

As previously outlined, the importance of this is vast - because seasonal wavelength changes from Spring to Summer  would lock in this type of default for periods during June, and possibly July in much the same ways as, by way of a few examples, during 1994, 1996 (to some degree) and 2006. Most of those years also had some Nino upstream forcing attached to them - and 2006 perhaps closest in this respect with an establishing and growing +QBO phase which helped supress sustained higher latitude blocks and facilitated low heights over the pole to follow the blocking of seasonal transition.

The most recent post discussed some of the elements that could make things go wrong, and which also would encourage Atlantic blocking mechanisms to become the default instead - and which would persist or follow on from the upcoming unseasonal supressed jet stream  conditions.

So of course there is nothing inevitable about such repetition in 2019 

However all three of the aforementioned years (1994, 1996 and 2006) saw highly underwhelming May's with a supressed jet stream and plethora of Atlantic/Greenland blocking prior to very good June and July's - but summer variants followed this in each case centred around extended dry very warm/hot settled spells and some spectacular thundery breakdowns and re-loads of the Atlantic trough and European ridge pattern. 1994 was especially notable for the thundery variant during both June and July.

 

Edited May 1, 2019 by Tamara

[MATTWOLVES 3]

Great Post as usual Tamara, now after letting that all soak in.... Just one question..... Is it going to be a nice summer or what!

[Methuselah]

Methinks there'll be quite a few brass monkeys keeping their hands in their pockets, this weekend?

 

[MATTWOLVES 3]

2 minutes ago, Ed Stone said:

Methinks there'll be quite a few brass monkeys keeping their hands in their pockets, this weekend?

 

Hopefully a 7 day itch Pete.... Things perhaps improving the following week! Oh by the way I'm a bit concerned by that 2nd chart.... How rude Mr GFS.

[Frosty.]

It's actually not going to be a bad weekend for most, plenty of sunshine and if you can get out of the chilly breeze it will feel pleasant but slight overnight frosts too..could be worse.

[Frosty.]

Certainly a cold snap for the time of year on the ukmo 12h with air straight from the arctic (northern scotland bearing the brunt of it)  but on the plus side it's clean clear air with great visibility, some showers, mainly for counties bordering the north sea and for the far north where they will have a wintry flavour but plenty of strengthening early May sunshine to compensate for the cold nights with widespread frosts, the frosts  sharper outside of towns and cities.

Edited May 1, 2019 by Frosty.

[Methuselah]

The 12Z gets off to a rather poor start and doesn't really get a whole lot better:

 

And, a usual, Day 16 is nae too bad. So brass monkeys can finally refrain from pocket billiards!

[Craig84]

Plume alert....

[Scorcher]

5 hours ago, Mattwolves said:

How can you fail to see a way out of the current output! Firstly the models may look completely different inside the next 24/48hrs, and secondly its the 1st of May! Alot of fine lengthy summers come on the back of cold/cool unsettled spells in late spring. It's hardly throw the towel in is it! I would be more worried if we was locked into a continued heatwave through May! For example it peaking to soon. This is a slight blip in what is sure to be a summer of many fine, very warm spells! Let's remember folks, it's the 1st of May, not the 1st of July! I thi k to many have got lulled into a false sense of security because of the last couple of very warm spells!! Let's not forget those spells were a tad premature! Refrain from towel throwing just yet folks..... Please!!! 

I don't think my post was that extreme to suggest that I was throwing in the towel...but perhaps it did come across as being overly pessimistic.

I do really enjoy May as a month and last May was really stunning around these parts- we were spoiled. It would be a shame if half of the month is cool and unsettled...but there is plenty of time for things to change, I know.

[knocker]

Amplification of the east European ridge results in the Scandinavian trough becoming negatively tilted which opens the back door for the Atlantic to mosey in. Quite a bit of cold air around

Edited May 1, 2019 by knocker

[Methuselah]

This could be an interesting coming together?

 

[Mike Poole]

1 hour ago, Mattwolves said:

Great Post as usual Tamara, now after letting that all soak in.... Just one question..... Is it going to be a nice summer or what!

First, agree really informative and interesting post from @Tamara.  Secondly, yes I still believe it is going to be a nice summer, but we have to get through some less summary weather first.  

There's big upheaval going on in the stratosphere with regards to the final warming.  

During April, the zonal mean zonal wind in the stratosphere has gone from +2 standard deviations from average to -2 standard deviations.  

I think it is difficult to link cause and effect with the weather with any degree of certainty, but I think this rather dramatic warming is influencing the weather currently predicted in the models - which certainly isn't what I was predicting for this time around mid-April.

But this influence should be fairly short lived.  You can see the cross polar ridge dissipate on the GFS 12z out to T192:

But this shenanigans in the troposphere and stratosphere will time out, while other drivers supporting a hotter than average summer remain, such as sea surface temperatures, yes in the Pacific, but more importantly perhaps in the Atlantic sector:

This pattern has been consistently referred to in the UKMO 3 month forecast.  

So, heat seekers, wait this current period out, I'm optimistic summer will show its face mid May! 

 

[MATTWOLVES 3]

Top class post Mike, we really are privelaged here on netweather to have so many insightful and astute posters... And I fully agree with your post, but you put it better than I would have.. Onwards and upwards after a short blip..

[Methuselah]

By the very end of the 12Z FV3, the vortex remnants seem to be on their last legs; a situation that I for one can't wait to happen...

 

The average temp ensemble is, as is often the case in May, all over the shop:

As for precipitation (in East Anglia)...there actually be some: 

[knocker]

An unusual event in May. Rapid cyclogenesis over Finland tomorrow

[Frosty.]

The Ecm 12z eventually shows tropical maritime air sweeping in from the southwest so the rain should be a bit warmer.

Edited May 1, 2019 by Frosty.

[knocker]

The ecm has the trough to the north east remaining influential throughMon/Tues with a front struggling south on Monday and showers on both days and both quite cold with temps way below average. The trough to the south west does make inroads Weds but very cold still in Scotland.

[Frosty.]

A crumb of comfort from the Ecm 12z is that it ends milder / warmer than the 00z..but probably wetter

[Craig84]

ECM sniffing around a plume at 240hrs too.

Pressure falling around Greenland and the trough pulling back west into the Atlantic.

Letd hope this trend is built upon in the coming days. 

[Frosty.]

I see similarities between the Ecm 12z operational / ensemble mean at day 10 so although T+240 is a very dodgy timeframe, if it's right it could herald a much warmer spell further ahead as the trough to the west digs well south we would initially bring tropical maritime air from the azores and beyond and then potentially scoop up air from southern europe / north africa..all a far cry from the arctic air set to flood down across the uk.

[knocker]

The EPS mean 5-10 anomaly this evening has a highly amplified Europe with the positive/negative tilt ridge/trough combination with a complex arrangement upstream involving a high cell and positive anomalies in the Labrador straits and an elongated trough in the north west Atlantic The upshot of all this is a strong westerly upper flow exiting the north east seaboard and running south of the trough across the Atlantic before impacting the UK. It does diverge just to the east to the courtesy of the aforementioned amplification..Ergo unsettled with temps below average.

In the later period a watered down version of the this with the upper flow abating over the UK as it diverges a tad earlier so more settled and maybe the temps creeping above average.

[knocker]

Outlook - cold air flooding south into Europe over the weekend

The 500mb NH profile and the Atlantic surface analysis for midnight and the 0300 UK chart

Some cloud and bits and bobs of rain still lingering in the NE and particularly the SE (note the temps at 0300) This will soon clear giving a fine and warm day away from Scotland. But showers currently over N. Ireland will spread across central and south east areas of England during the day and some of these could well be heavy with hail and thunder in the mix. Further north the cold front associated with the trough over Scandinavia is tracking south and this will bring a band of rain across Scotland, snow on the mountains, and introduce much colder air in it's wake. Added to that there is a convergence zone running across the north of England which should pep the showers up a tad

Cloud and some showers will still linger across central England, around the front,  through the night with more showers over Scotland in the northerly wind which will be wintry and of snow on the higher ground.

The cloud and showery rain still tracking slowly south down England Wales on Friday with a continuation of wintry showers in Scotland on the freshening wind and these may push down the north east of England. A much colder day generally with the exception of the south west

A cold day on Saturday in the fresh northerly wind as the subtropical high ridges to the west with wintry showers in the north and down the eastern half of the country/ Tending dry and sunny in the west after a widespread frost generally

Another cold day and sunny day on Sunday but, after a  widespread frost, with the wind easing feeling warmer. Still showers likely in the stronger breeze down North sea coasts

By Monday the upper trough is starting to take on a negative tilt but on the surface another weakening cold front is tracking south with a band of showery rain effecting some areas but generally sunny with still temps a tad below average after another widespread frost

Edited May 2, 2019 by knocker

[knocker]

By Tuesday the pattern is well into transition with the Atlantic popping through the open door and a trough arriving from the west with strong winds and some much needed heavy rain

For the rest of the week low pressure in charge so periods of showers and longer periods of rain, interspersed with sunny intervals. Temps still averaging a tad below average. This is of course courtesy of the gfs

 

 

[Frosty.]

To me the most interesting thing about the Gfs 00z operational is the ending with +15 850's lurking just to the south..gets me in the mood for summer!!

[knocker]

The ecm has a low 976mb WSW of Ireland midday Tuesday with the fronts into Ireland and this fills slowly and tracks east so rain and strengthening winds overnight and through Wednesday for the UK. Temps still below average and significantly so in Scotland