Model Output Discussions 12z 01/06/2017

[draztik]

Temp anomaly, ecm ens, days 6-10... quite the change from earlier this week! 

[Frosty.]

Quite an autumnal looking Ecm 12z ensemble mean tonight regarding next week with generally below average temps, indeed, very cool and breezy / windy at times with spells of rain..not ideal weather for high summer

Edited June 22, 2017 by Frosty.

[Fourty Point Three Degrees]

This mornings 18z looks awful next week. It sure will feel like late October instead of high June with max temps ranging from 13 to 17C. Hints towards the end of the run of HP approaching the SW. But next week only the daylight hours will give the feel of summer.  

Edited June 23, 2017 by 40*C

[knocker]

A very brief overall picture. In the ten day time frame the gfs this morning continues to indicate that our weather within that period will continue to be dominated by low pressure. Initially by the trough in eastern N. America from which a very strong jet blows east then SE and then by the low over the Arctic moving closer to Greenland and interrupting this flow with the help of some ridging in the western Atlantic. Before once more seeing energy from the eastern seaboard dominate.

Meanwhile back on the farm. By 12z Sunday our current depression has tracked E/SE and is 989mb west of southern Norway whilst the next Atlantic low is poised some 400km west of southern Ireland. This tracks NE to be 992mb Hebrides by 06z Tuesday whilst another low swings in rapidly from the eastern seaboard courtesy of the aforementioned jet. The associated fronts will bring rain Monday/Tuesday, mainly in Scotland where the winds will also be quite strong.

From this point the second low tracks east into the UK forming a complex area of low pressure over the UK as ridging in the Atlantic temporarily cuts off the energy flow from the west and introducing a very showery regime to all of the . But of course that's not the end of the story as the direct conduit to the eastern seaboard is reestablished and by the weekend we once more see depressions swinging in from the WNW

So in a nutshell next week looking unsettled, initially more so in the north, with showery rain just about everywhere with temps around average then dipping below. But this is such a complicated scenario that, certainly from around mid week, a watching brief is the best option.

 

Edited June 23, 2017 by knocker

[Frosty.]

It looks like an increasingly cool unsettled outlook, feeling more like Autumn than summer as time goes on.

[I remember Atlantic 252]

22 minutes ago, Frosty. said:

It looks like an increasingly cool unsettled outlook, feeling more like Autumn than summer as time goes on.

and wouldn't happen in winter post 1998, this is like 19th Nov '96, snowmaker low, nowadays can only happen between Apr and 0ct

even if it happened in winter, somehow as late as 2017, would be rain and sleet

 

Edited June 23, 2017 by I remember Atlantic 252

[Frosty.]

Just to back up what I said about autumnal, that is what the Gfs 00z shows, rain, wind and even cold enough in places for ground frosts..summer in the uk 

Edited June 23, 2017 by Frosty.

[I remember Atlantic 252]

not too bad Frosty, okay in March this, at least for the south

[Scorcher]

17 minutes ago, I remember Atlantic 252 said:

not too bad Frosty, okay in March this, at least for the south

Awful, before 2007 I used to believe those sort of maxes weren't possible in July, having lived through mainly only decent/good summers up to that point (within memory).

2012 showed just how bad it can be in the UK even in summer as well- we're not guaranteed to get out of the low teens if the conditions are bad enough. The outlook could not be much worse in terms of temperatures this morning.

One crumb of comfort for me is that there were some very cool days even in June 1976 in these parts- there was a max of 13C in Manchester only days before the heatwave began. So it can change around quickly.

[knocker]

The ecm pretty much on the same page as the gfs and by Tuesday 18z has a complex area of low pressure over the UK/France/Spain and points east. Much convective activity with temps ranging from 12C in northern Scotland to 22C in downtown Basingstoke. This remains the situation for the next 48hr but by then the low has slipped east to Denmark and thus the surface wind has veered northerly resulting in temps down a tad in the south to around 17C and this remains the case on Saturday

From this point the depression briefly intensifies, strengthening the N/NW flow before moving and preparing the ground for the next low west of Ireland by 00z Sunday.

So not that bad mid week, sunshine and showers, but the end of the week requires further consolidation.

I'm also pleased to report that Sidney is scaling the heights once more after the heat laid him low

Edited June 23, 2017 by knocker

[Frosty.]

The Ecm 00z follows the Gfs with an increasingly autumnal spell next week with temps dipping below average and lots of rain / wind.

Edited June 23, 2017 by Frosty.

[mb018538]

Unusual to see a jet profile like this heading into July...



The entire UK on the cold side of the jet! Now if we could just manage a similar chart in January....



Not a great deal to take from the ensembles this morning either. Yesterday's slight trend to drier/warmer by the end of the runs is still just about there, without being clearly defined.

[Frosty.]

One really needs a sense of humour with the British climate, we are going from in some places intense heat to very unseasonably cool and unsettled, it's especially hard on scotland where summer has failed to even begin yet..really autumnal looking charts later next week with buckets of rain, strong winds and even slight ground frosts during short-lived calmer interludes.

[Sky Full]

The models seem to be set in a pessimistic phase with autumnal weather being predicted for what should be some of the warmest weeks of the year.  These images are from the GFS showing the end of June / early July:

  

But the last two charts are predicting conditions over 200 hours away and the chances of them verifying are frankly miniscule, in my opinion, based on the frequency of the u-turns made by all the models, all the time.  The only reliable charts are those for the next 96 - 120 hours really, and anything beyond that should only be seen as a possible trend at best, and pure fantasy at worst.  I wouldn't write off July yet by any means although it has to be said Wimbledon often brings out the worst in the weather!  

I do wonder why the models seem capable of occasionally predicting quite wild swings away from the seasonal norm at some distance out, as I would expect their algorithms to trend toward average conditions the further into the future they try to predict.

[Frosty.]

I don't think we should write off July, it was predicted to be a cool unsettled start and that looks like happening but I've also heard on the grapevine that July will show a marked improvement as the month goes on with increasing warmth and high pressure plus continental influence bringing heat and thundery showers so although the models are painting an unseasonably cool and unsettled outlook as next week progresses..in the great scheme of things it could just be a minor blip with summery weather returning strongly next month..even to Scotland!

[mushymanrob]

14 hours ago, damianslaw said:

The models are showing an unusually active atlantic next week, with a strong jet steamrolling across the country, mmm ominious not very good signal for the remainder of the summer.. usually takes until late August before we see such power.. 

 

indeed the strong jet stream will prevent any rise in pressure over the uk, as long as it holds its current position and strength.  but i dont think it will, not that i can back that thought up with any data, it just doesnt seem likely and when it does weaken/buckle/shift, as long as its not southerly tracking we will then get more heat via rising pressure.

of course rising pressure, which id have though was likely given the current longwave pattern, doesnt always mean heat..... summer 1979 was very dry but not hot.

[Frosty.]

Woeful temps next week for scotland, barely reaching double digits celsius at times and struggling to reach 17/18c in the south..feeling more like late September than the height of summer. A very unseasonably cool unsettled trough dominated spell developing next week on the Gfs 6z.

[knocker]

16 minutes ago, mushymanrob said:

indeed the strong jet stream will prevent any rise in pressure over the uk, as long as it holds its current position and strength.  but i dont think it will, not that i can back that thought up with any data, it just doesnt seem likely and when it does weaken/buckle/shift, as long as its not southerly tracking we will then get more heat via rising pressure.

of course rising pressure, which id have though was likely given the current longwave pattern, doesnt always mean heat..... summer 1979 was very dry but not hot.

Ye quite and if we did manage a change to the upstream pattern and some renewed amplification mid Atlantic, which combined would interrupt the jet, then this wouldn't be an ideal route to more WAA from the south

Edited June 23, 2017 by knocker

[Singularity]

 

Some weakening of the jet stream and return toward Atlantic trough/UK-Euro ridge pattern on the GFS 06z but only short-lived and a whole 10-11 days away. I continue to believe that the pattern should not, given the base state, become as 'stuck' in a poor configuration for us as some runs have lately been suggesting, but that belief has taken some hits over the past few days and is finding it harder to get back on its feet after each new blow.

That's the best I can do for an alternative take this morning 

[Tamara]

Anyone remember early February and the MOD hopes and excitement for seasonal snow/ cold when high pressure set over Scandinavia, backing cold air westwards and seemed set to retrogress towards Greenland to usher in the first cold spell with real snow potential and maybe the best seen for a few years?

Now think of this month and the glorious pattern that set up for the hot spell which has just departed.

Next look at this plot of (rolling forward) current year total atmospheric angular momentum and see how the peaks of AAM have corresponded with arrival of the the two desired patterns. BUT, where in both cases large downward corrections have immediately then occurred, relative to the base state - and consequently in turn scuppered the duration of both desired patterns ....with the result that both winter 17 and now the latest summer 17 hopes have been aborted...

The difference is of course that we are only in June and there is plenty of time for changes back to the better to banish the latest spoiler, though we are also always mindful of jam tomorrow.

As that wonderful heat ridge was building a week back, I was already aware that as much as the constructive atmospheric circulation for downstream summer ridges that had in evidence since the recovery from the early Spring slump in AAM was sending us its biggest reward (that is of course  if you like summer heat); the switch was already in place to ensure that while we made one temperature milestone tis week to match June 1976 ,we already looked set to see the same sort of pattern (as in 1976) get into trouble just at the time that this infamous summer was getting into its stride from almost exactly to this date that particular year.

A pattern that lasted a remarkable period due to El Nino forcing and a buoyant AAM state. Just a few of the charts from June into July that year, that make you think what might have been similar this year - when instead we are looking at a pronounced change to something more akin to autumn

.

The Global Wind Oscillation, which is a representation of combined tropical and extra tropical wind-flows that determine rossby wave length (and therefore associated jet stream velocity, trajectory as framework for NWP synoptic pattern right across the hemisphere, has reflected the slump in AAM with an orbit into La Nina-esque forcing territory (Phases 1, 2,3) for the first time since last year - and eclipsing the amplitude of the lower orbit seen in February.

NB: The WDT site produces consolidated data for both tropical and extra tropical forcing and is therefore highly accurate as a retrospective calculation in terms of GWO phase space than the GFS Schiraldi product often seen posted on here which is based on forecasted data assessment and tends to bias the tropical forcing element of the AAM budget at the expense of the extra tropical

For clues why the GWO might have produced a lower amplitude orbit than the last pronounced drop in February, we can look at what has happened to the Pacific ENSO zones in terms of temperature trends over the period.

We remain in the same ENSO neutral officially that has prevailed for some considerable time now, but have just switched from a "constructive" (Nino like) atmospheric circulation relationship to that base state to a "destructive" (Nina-like) relationship to that base state. Several months back the most eastern Pacific zone 1.2 was warming markedly ahead of the western zones and led a heating trend from east to west that gathered momentum through the Spring. We have recently seen a marked drop off in temperature in the 1.2 zone with resurgent tranches of trade winds (easterlies). This tells us that westerlies are being scrubbed from the atmospheric circulation from the tropics c/o convection and rainfall patterns and the attempts of migration across the ENSO neutral spectrum to enter weak El Nino (as forecasted by most model forecasts during the Spring) have been halted.

 

These trade wind easterlies are connected to intra-seasonal tropical convection signals in the Indian Ocean and at the expense of reversal of the Nino-like westerlies (which configure the downstream rossby waves to promote an Atlantic trough and downstream Euro ridge) . These upstream changes have finally started to fully impact our pattern downstream. They are responsible for the aborting of our latest and greatest heat ridge after a late Spring and early Summer sequence that has seen repeated Western European ridge amplifications and warm air advection between the ridge and the Atlantic trough.

This pattern reversal has started to come about this week through the ascendancy of an amplifying Atlantic ridge as upstream forcing in the eastern Pacific starts to build pressure there having the effect on the long-wave pattern in terms of retrogressing the Azores ridge. With the mechanism for eastward Azores> Europe ridging gone and pressure higher well to our west we have seen the Euro ridge decay and the jet stream trajectory change from SW>NE through W>E as currently and ultimately once the Nina like forcing is completed from upstream NW>SE.  This NW/SE profile is well advertised in all modelling from the 5/6 to 10 day period and theeafer.

No surprise that the resultant temperature changes will be something of a shock to the system with maritime airflow from more northern latitudes replacing the  warm tropical maritime and hot tropical continental airflows of the Atlantic trough/ Euro ridge regime.

I spoke some time back about a flip to an Atlantic ridge/downstream trough scenario as being counter intuitive relative to the background signals. And it was counter intuitive to those signals. The explanations are given above, but nevertheless whilst these were reasonably anticipated, the amount that atmospheric angular momentum has fallen has surprised me based on perceived trends for the summer that looked set to maintain some buoyancy.  The new pattern set-up is far less counter intuitive to say the least.

A bit too premature yet, but its possible some reanalysis may be required based on the new lower benchmark offered than the late Spring/start of summer ushered in and from which the atmosphere will be resurrecting itself from, once the upstream forcing starts to head eastwards again. For that to happen we would need to see loss of the I/O forcing, and eastward progression of topical convection as suggested by this particular modelling

The V200 profile for MJO related tropical convection suggests that we may to wait till the second week or so of July for real improvement. Should it occur, I would treat any NWP operational output over the coming short and medium term period that shows the Azores ridge moving back in any meaningful way as a false dawn

The latest EC weekly also suggests improvement from the SW might start to occur from week 3 (effectively the second week or so of July)

It might be a slow process.

Weeks 1 and 3 pasted here for information. Whilst the usual obvious caveats with these suites apply, they do tally with tropical forcing expectations so at least some provisional credence can be given.

 

The upstream forcing that would need to be sufficient to deliver an improvement (beyond a very brief transitory toppling ridge) would be by a representation of the GWO breaking out of any Phases 1,2 and 3 tighter orbit and heading back more towards a Phase 4,0,8,4 tracing pattern. This, as a reflection of enough renewed angular momentum tendency to switch rossby wave lengths sufficiently to force the upstream wavelength back eastwards, knocking out the amplified Atlantic ridge (changing the jet profile back to SW>NE in the process)  and consequently building strong enough downstream ridges for warm air advection to return.

Two further factors/indicators can be included in the discussion and remain encouraging for some kind of returned equilibrium re-set. The SOI is currently showing no appetite to take the atmosphere/ocean relationship further down the road to cementing the kind of Nina feedback that would threaten a larger portion of the summer. This remains very much the right side of neutral - with no daily returns tanking into proper positive territory

 

Also the stratosphere/troposphere profile from top to bottom remains solidly on the cool side which means that arctic heights cannot exacerbate even further the upcoming cooler and more unsettled pattern by keeping supressing the jet stream, and then in turn hampering things when the upstream Pacific pattern improves

 If we think back to the unsettled blip in the first week of June with that deep low of the 6th - what was notable about it was that it occurred during a period when the troposphere levels briefly warmed (as represented by the deeper orange spike) but we were within the +AAM atlantic trough/euro ridge regime, which meant that it was fast and easy to flip back to a much warmer pattern, once heights fell again to the north, with the default for warm air advection already in place.

So indeed the pattern improved - almost immediately for SE UK, and then with a few fits and starts for the greater part of the country.

Under the low angular momentum regime as happened in summer 2007 there was the double whammy of also having an anomalously warm arctic profile with both drivers acting to sustain the jet and pressure patterns at unseasonable latitudes with both Atlantic and arctic heights dominating our sector.

We are minus that in 2017, so once AAM tendency recovers, this should assist the speed of attempted improvement.

So at this stage any reanalysis certainly remains on the back burner, and its a case of sitting out some decidedly underwhelming model viewing for the next week or two

 

 

 

 

 

Edited June 23, 2017 by Tamara

[richep]

Metoffice outlook sounds quite promising from week two onwards 

[I remember Atlantic 252]

1 minute ago, richep said:

Metoffice outlook sounds quite promising from week two onwards 

not there on GFS, but better for day 1, could be upto 25° at Wimbledon

[Fourty Point Three Degrees]

Radio Key 103 said earlier that there is no more dry, sunny weather expected for at least a month!
GFS has come in with a much wetter end to the week than other solutions, the seemingly stubborn upper trough refusing to budge and allowing another low to get caught up in it.    

        
 

[Frosty.]

The most noticeable thing about the Ecm 12z is it isn't unseasonably cool next week, in fact its quite warm and humid but still unsettled with even some thunderstorm potential and it wouldn't be raining all the time, there would be some warm sunny spells too.

Edited June 23, 2017 by Frosty.

[knocker]

Not too much waffle vis the anomalies this evening as there is little change from last night. Suffice it to say with the Azores nudging north in mid Atlantic and the trough dropping south into France the upper flow is north of west and with a tight thermal gradient the strong  jet tracks down south of the UK. This ties in pretty well with this evening's det. outputs In the 10-14 period a flattening of the pattern with LP the NW and HP to the SW thus a westerly flow and a continuation of changeable weather

Edited June 23, 2017 by knocker