Model Output Discussions 12z 01/06/2017

[Frosty.]

Looking at the Gfs 6z operational, becoming warmer across England and Wales and more humid for a time with max temps into the low to possibly mid 20's c but becoming very warm in the south / south-east with temperatures into the mid / upper 20's celsius and thursday looks the peak potential for some big thunderstorms. Beyond Friday it becomes cooler and fresher from the west but drier and brighter, especially sunday. Next week shows a changeable trough / ridge trough Atlantic pattern with temps struggling to reach average in the south and cooler than that further n / nw.

Edited July 4, 2017 by Frosty.

[phil nw.]

A couple of posts have been removed for being off topic.

Model output discussion only please ta.:-) 

[mb018538]

Wouldn't worry too much about later next week yet - far from certain! Back to joe average, and I guess we will see where it goes from there.

[Singularity]

 

Familiar ground here as the jet stream strength and 'flatness' is reduced nearer the time.

So it is that the models are toying with yet another shallow low dropping down west of the UK by Monday. Question is whether we again see a breakaway ridge from the Azores manifest, or have to put up with the low drifting slowly but surely across our lands Tue-Wed.

Either way, with the sting taken out of the Atlantic westerlies, there's an increased likelihood that the Azores High will manage to build far enough N that the next push from the west drives an extension of high pressure over to the UK with the jet stream tracking to the north of us. Hopefully this shift will be the start of a trend but I'd not be surprised to see the models remain unsteady in their corrections, just to test some nerves .

It's such a shame the way the GLAAM bias causes the majority of GFS runs to try and turn things cool and unsettled by the 12-16 day period, but at least it's keeping people's expectations from becoming unreasonably high .

[Man With Beard]

The outlook puts the UK on that line between the settled and the unsettled. So typical of many of our July's of course. Next week looks less settled on ECM but how many times have we seen those slight corrections north? I don't think it'll end up too bad in the south, more changeable for sure in the North where let's be honest, summer looks far away.

[draztik]

2 minutes ago, Man With Beard said:

The outlook puts the UK on that line between the settled and the unsettled. So typical of many of our July's of course. Next week looks less settled on ECM but how many times have we seen those slight corrections north? I don't think it'll end up too bad in the south, more changeable for sure in the North where let's be honest, summer looks far away.

 

 

 

Wimbledon should hope not; ecm 12z (as per weatherbell) showing max temps on Friday 4 July (midday) to be in and around 15C for the London area

Edited July 4, 2017 by draztik

[mb018538]

Yeah, ECM looks ropey tonight. Most models are favouring low rather than high pressure to be more dominant. Time for corrections of course, but not the best set of output this evening.

[Frosty.]

5 minutes ago, mb018538 said:

not the best set of output this evening.

Not the worst either, the Gfs 12z looks pretty good for the second half of next week with the azores high ridging in. My view is next week at worst will be changeable with the usual n / s split and at best..something like the Gfs 12z shows..charts I posted further up the page.

[Fourty Point Three Degrees]

30 minutes ago, Frosty. said:

Not the worst either, the Gfs 12z looks pretty good for the second half of next week with the azores high ridging in. My view is next week at worst will be changeable with the usual n / s split and at best..something like the Gfs 12z shows..charts I posted further up the page.

Straw clutching?

Both ECM and GFS were poor with a suggested unsettled and cooler period being most likely next week.  ECM ends with vile 850s and a very autuminal 997mb low in the SE 

[Summer Sun]

2 minutes ago, 40*C said:

Straw clutching?

Both ECM and GFS were poor with a suggested unsettled and cooler period being most likely next week.  ECM ends with vile 850s and a very autuminal 997mb low in the SE 

I'd give the ECM Op another few runs yet when looking at the ens

 

[Singularity]

We'll see... I find it hard to take the longer-term ECM seriously until if and when the MJO actually does make a jump into phase 2/3 as the model has been predicting for 1-2 days ahead without success for over a week now.

[Frosty.]

To me its a bit silly worrying about a day 10 ecm chart when we are seeing an increasingly warm spell this week..temps into the 80's F further south for the next 3 days or so..even saturday could still be very warm in the SE.

[Tamara]

On ‎23‎/‎06‎/‎2017 at 17:41, Tamara said:

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

Extract from previous post copied for continuation purposes 

A few things posted over the last couple of weeks that offer the chance of some perspective:

1) Assumed NWP atmospheric angular momentum bias

Once again, its worth repeating here that the signals lead the models, the models do not lead the signals.

Since the step-change in the atmospheric circulation (sudden drop in atmospheric angular momentum) that led to the abrupt change in the weather during the last third of June from mid month heat (for many) to cool and unsettled (for all of us)  low AAM bias expectation has much less relevance in terms of NWP evolution.

(The previous post explained in a lot of detail why the change had come about and what the causes were).

 To put this into some synoptic parlance, any individual model suite operational (and even ensemble data) which has suggested any especially purposeful eastward return of the Azores ridge has risked being built around conceivably erroneous assumptions that modelling is auto-correcting from Nina-esque forcing in the Pacific.

I think that repeated use of the GEFS forecasting tool for purposes of checking the progress of the Global Wind Oscillation (which is a plot representation of the flux of global windflows/ Jetstream strength and trajectory as calculated through tropical and extra tropical forcings)  leads to assumptions being made that the inherent low angular momentum bias within the product is applicable at all times.

As stated in previous posts, checks on consolidated actual data is required to get as accurate a perspective as possible on where the atmospheric circulation actually is, instead of using GEFS forecasted data to build in a forecast assumption that this is a 24/7 perma-default subject to persistent over-estimation of Indian Ocean tropical convection forcing.

A bias does certainly exist, but its knowing the times when its bias is much less of a factor. This was also a challenge last summer which saw a low angular momentum phase during the first half of the summer due to I/O tropical forcing destructively acting on the pattern in the Pacific at a time when ENSO was transferring through into ENSO neutral > very weak La Nina later in the year

The WDT site shows that the GWO was stuck in low amplitude low angular momentum Phase 2 for much of the last week

The retracted Azores ridge and Western Europe trough seen up to the weekend is fully representative synoptically of this phase at this stage of the summer.

So to the present and outlook:

The highlighted post from two weeks back suggested we would need to see the GWO progress back up towards Phase 4 (recovery upwards of AAM) to initiate any more sustainable recovery without slipping back to a more withdrawn Azores ridge and the trough having a greater say once more. 

Latest modelling is inclining back to retracted ridge for next week and cooler changeable regime more widespread again.

I suspect the consolidated data updating through this week will show that there has been an attempted orbit to GWO Phase 3/4 but that an intermittent tropical signal from the Indian Ocean continues to hamper efforts (for the time-being) to revert the atmosphere back closest to where we were prior to the breakdown of the mid June heatwave.

This interim partial recovery, largely driven by some +AAM transport into the atmosphere c/o a +ve mountain torque across the Andes - spiking sub tropical ridging to mid latitudes over the 'wavelength' (lifespan) of this torque wave eddy (circa 5/6 days) means that the ridge extension and cut-off low this week allows the window for return of summer proper at least for southern and some central parts of the UK 

But. this transitory amplification aside, caution is definitely required against any on-going supposition that the models are underestimating the AAM trend over the coming week (commencing 10 July) and therefore assuming that any model forecasts for next week showing the flat pattern and the retracted Azores ridge and Icelandic low interplay are overdone. They likely are not overdone, and so expectations should be adjusted accordingly.

Tropical convection forecasts are subject to uncertainty, but such uncertainty on balance still favours another cooler and more generally changeable period, until at least the mid month period.

Its not a surprise to see some revision of expectations of more wholesale and wider improvement in status updates from the likes of the METO - when eastward forcing of the tropical signal continues to remain at some distance and in the absence of consensus.

Supression of the I/O signal and eastward forcing would help the rossby wave pattern configure towards greater eastward progression of the Azores High (closer to what was seen mid June) and as a consequence more widespread warmer and more settled weather than the relatively brief (but highly welcome) interlude this week offers. But lets remember its not for all of us and those in the NW of the UK will see this pass by once again

There is no reason not to expect a return to more widespread warmth and settled weather later this month, but until a greater modelling consensus from the tropics happens then false dawns continue to be a risk

2)  Arctic heights - the stratosphere>troposphere profile

In terms of anticipating hoped for improvement, we can continue to look to the profile of the layers of the atmosphere retaining low heights to the north. It has been argued that this is accentuating thermal gradients and spawning low pressure systems in terms of the cold air locked to the north and the seasonally much warmer sub tropical air to the south. - therefore hampering a seasonally warm and settled summer pattern for the greater of the UK.

However, in the absence of arctic blocking, the other side of the coin is that the AzoresAtlantic ridge is prevented from amplifying further to our west to lead to greater and deeper cool air advection southwards as heights are raised across the pole, locking in the cooler spells for much longer than seen so far. Such as seen in the poorest summers of recent years such as 2007 and 2011, which were both dominated by the double whammy of low atmospheric angular momentum and anomalous arctic high pressure.

From the present position of cold stratosphere/troposphere height anomaly layers, still persisting robustly as June has turned into July, it remains a much easier route back to proper summer conditions - much as the last few weeks has already demonstrated

So this too, augers better for the next return of summer proper later this month. But for this to happen, the fortunes of all, and not just the south depend upon some awakening of tropical convective forcing moving eastwards, with suppression over the I/O, to enable the Jetstream to move north of the UK and Azores ridging to be stronger and more sustained into Europa - as atmospheric angular momentum returns to buoyancy.

 

[A Frayed Knot]

Like i said in the Past ' All computer models you are dwelling on' even last week it was looking grim and droom ' the last 2 days here have been great ' even Hotter here 2day and even Thursday ' stick to Met Office .. Not ECM -GFS - ANNADIN IS GOOD FOR YAH

[weatherguru14]

How can you take long range models serious like  the GFS in particular  one run it as a massive heatwave.. next run looks like winter..

[mb018538]

Think we can safely say once Saturday is through, we won't be seeing any heat for a little while again. Pattern looking pretty flat. It's frustrating to see the Azores High parked so far out west, it's just not close enough to be a big influence on our weather. Looking likely we are going to have to plod through a load more nothingness before perhaps something warmer and more settled turns up after mid month.

[Singularity]

Thanks for the update Tamara

I retain the suspicion that the atmospheric state is not far enough from neutral to lock in a retracted Azores ridge for much time so will continue to watch for weak ridges producing a warm/very warm day or two, but must concede that I did not adjust my AAM corrections down fast enough after the recent underestimated ascending period. So next week does look likely to be changeable with temps mostly varying around average or a little below - but still the chance of an appreciably warmer day or two at least in the south.

I do however still view the GEFS week 2 drop of AAM as unrealistically large, as barely a day has been seen in the past year in which it wasn't overdone. So too much drive toward establishing or maintaining a cool and unsettled regime. Good thing is, most on here don't take GFS very seriously at that range anyway

Edited July 5, 2017 by Singularity

[Glacier Point]

Just worth bearing in mind how the models have been handling events just recently...

ECM mean 500 hPa height anomaly day 10 ten days ago:

And the initialised version:

Broadly OK across the NH but a little off in the NE Pacific, but quite a way off for our corner. Way too flat with the Azores ridge and didn't capture the split flow in the NE Atlantic.

A relaxation in angular momentum looks about right given tropical developments, but no where near GFS projection. I'd go closer to seasonal norm, possibly a touch below for AAM state. Expect once again the trough in our locale not to be modelled correctly in the day 10+ timeframe.

[carinthian]

This chart from UKMO at 144t puts the upper trough in one of the worst possible positions and can be difficult to dislodge. Seen this set up in some of the worst summer seasons. The extended charts show a possible 10 day unsettled spell. Thereafter, hopefully for a better second half for July but we will have to see a major pattern change.

 C

[mb018538]

8 minutes ago, carinthian said:

This chart from UKMO at 144t puts the upper trough in one of the worst possible positions and can be difficult to dislodge. Seen this set up in some of the worst summer seasons. The extended charts show a possible 10 day unsettled spell. Thereafter, hopefully for a better second half for July but we will have to see a major pattern change.

 C

Yep, everything angled completely the wrong way. Strong jet piling out of Canada straight over the Atlantic, could be a bugger to shift. Not desperately unsettled, just not great for mid-summer.

[carinthian]

2 minutes ago, mb018538 said:

Yep, everything angled completely the wrong way. Strong jet piling out of Canada straight over the Atlantic, could be a bugger to shift. Not desperately unsettled, just not great for mid-summer.

Not an ideal place for the upper trough to be anchored from Southern Scandinavia to Norwegian Sea. Will result in cool rainy conditions for almost any location in NW Europe.

 C

[northwestsnow]

Beginning to worry this is going to be another of those ' nice down south and ruddy awful up north' summers..

Overcast and drizzle here, probs sunny and clear in the SE...

00z runs look poor after friday, bloody azores high waaaaaaaaay out in the west Atlantic leaving us at the mercy of lows to the NW.

Edited July 5, 2017 by northwestsnow

[Coopsy]

29 minutes ago, northwestsnow said:

Beginning to worry this is going to be another of those ' nice down south and ruddy awful up north' summers..

Overcast and drizzle here, probs sunny and clear in the SE...

00z runs look poor after friday, bloody azores high waaaaaaaaay out in the west Atlantic leaving us at the mercy of lows to the NW.

Isn't like that most summers? Yup blue skies and humid here. Looking at outputs relief isn't too far off from the weekend into next week for the south. Unfortunately nothing great for north  

[Frosty.]

Things are hotting up further south today, London could reach 30c this afternoon..becoming very warm and humid across the rest of England and Wales tomorrow but with an increasing risk of severe thunderstorms with large hail and torrential rain..it's another taste of high summer which last week didn't seem possible!..

[Glacier Point]

06z GFS being an excellent case in point. Little disturbances in the flow dropping to our west driving warmer air poleward. 

With the +AO signal, a flat Azores ridge is not straightforward and subject to the type of variation we are seeing at T0, T96 and possible again at day 10.