Model Output Discussions 12z 01/06/2017

[Summer Sun]

Looking at the euros it's ECM v UKMO

Until the track of Gert is nailed down expect wild swings from the models

[Matthew.]

The ECM looks better for warmth and big showers as Gert stalls. I don't think it's useful looking past 4 days at the moment.

[Singularity]

    

Well UKMO is certainly the ugly duckling with respect to the start of next week.

Given all but ECM paint a very dreary (but not all that wet down south) picture for what once looked to be a fine Sunday, it'd be sad to lose out on anything warm next week too, so here's hoping the consensus to stall the low out west - and the strong trend GFS has displayed in this direction having been as progressive as UKMO this morning - will count for something.

 
With any luck we could even score a shot of hot weather although odds are it'd be restricted to the SE'rn third or even quarter unless the stalled-out position of the low can trend even further west.

 

There are hints that the pattern will be changed for the longer-run rather than just briefly, but not necessarily in a manner that favours plenty of dry weather should the Atlantic jet keep on buckling as the ECM 12z depicts. It's one of those occasions were we could do with a nice straight section of jet extending east from the area of low heights in the vicinity of Greenland. That being the one thing UKMO plays nice with this evening. GFS would have been on par with that if it hadn't gone and made so much of low heights over Europe - that being something to keep an eye on too given what happened Wednesday of last week.

     

[knocker]

Well the ecm apart from ringing the changes from 00z is not without interest. The travels of the low (ex Gert) sees it west of the Hebrides at 00z Tuesday from where it moves slowly east and loiters in the vicinity of Scotland until saturday leaving the southern half of the UK in a light showery westerly..

But the travels of the low have also disrupted the high pressure to the west and an upper trough sinks south in the Atlantic over Thursday and Friday which phases with the low pressure over Iberia which spawns and unstable surface feature that tracks north to effect the south with some impressive convective activity on Saturday  Well it would be impressive in a more realistic time frame The trough then extends south initiating some impressive WAA into Germany.

I don't need to repeat that this is so different to the previous run and other models that next week is still a long way from being nailed down.

Edited August 17, 2017 by knocker

[ANYWEATHER]

If I was a betting man well GFS and ECM would be off my list

[knocker]

As mentioned yesterday it is very difficult to get a handle on the medium term outlook at the moment with so much variability in the system and that includes the anomalies. What, if anything the travels of TS Gert is contributing to this is above my pay grade, but it's very probable that it's having some impact. At the moment in the ten day period we are looking at low pressure in the eastern Arctic with a trough over Greenland and positive anomalies and some amplification of the Azores in the western Atlantic.

But with the high pressure being that far west a conduit is established SE from Greenland for a trough to be established SSW of the UK and a slackening of the westerly upper flow in the eastern Atlantic. This could lead to some interesting scenarios for the det. runs to get their teeth into as if they are not having enough trouble as it is.

Thereafter the indications are that the HP may slip east for a short period of more settled weather before a flatter Atlantic becomes likely. Usual caveats apply.

With the current depression moving away NE of Scotland over the weekend Saturday should okay for most apart from Scotland and certainly Sunday maybe for all but the fronts and rain from the next low will start impacting the SW Sunday morning and tracking NE.

By Tuesday 00z ex TS Gert has arrived west of NI and it's associated fronts are effecting there and Scotland but it's worth noting for later that the upper trough has split during it's travels and a separate low pressure area established west of Iberia.

By midday Wednesday the main low is over the UK where it has been joined by a weak feature tracking north east from Iberia. From here the main low tracks east and things get a tad complicated as the UK slips into a col area with low pressure to the SSW, HP to the north and a trough to the NW.. Which in fact is the precise scenario as indicated on the anomalies above. So on the surface we get a thundery low tracking NNE and the possibility of the odd system slipping into Scotland. This will obviously change in the interim but it's certainly not without interest.

So in a nutshell unsettled for the beginning of the week but the south largely escaping and more settled for all towards the end but with a few possibilities in the woodshed.

Edited August 18, 2017 by knocker

[knocker]

To confuse matter even more the ecm still differs with the gfs vis the track of TS Gert and thus the later evolution although it is paying lip service to the conclusion.

By midday Tuesday it is probably at it's nearest point to the UK due west of NI and about 20W and with high pressure hibernating north west weak fronts can traverse the UK

From here it gets a tad complicated as the low now tracks NW between Greenland and Iceland and is joined by another trough which duly splits with one section tracking south east to be west of Ireland 00z Friday and NW of Iberia 24 hours later. This is the lip service

All of this creates a slack, unstable low pressure area over western Europe for the weekend with a lot of showery activity over the UK, France and Spain.

In a nut shell next week would not be too bad with this scenario with periods of showery rain but quite warm at times in the slack gradient  Just to add, although this will be covered elsewhere, there will be some quite heavy rainfall on Sunday as the fronts from Gert track NE.

Needless to say this is subject to change.

Edited August 18, 2017 by knocker

[karyo]

The ECM is showing a hurricane in the Gulf of Mexico from 168 hours onwards which is a location that is going to make headlines if it materialises. 

It will be interesting to see if it is still there in the 12z run.

Edited August 18, 2017 by karyo

[Iceaxecrampon]

WOW!

[Nick F]

3 hours ago, knocker said:

As mentioned yesterday it is very difficult to get a handle on the medium term outlook at the moment with so much variability in the system and that includes the anomalies. What, if anything the travels of TS Gert is contributing to this is above my pay grade, but it's very probable that it's having some impact. At the moment in the ten day period we are looking at low pressure in the eastern Arctic with a trough over Greenland and positive anomalies and some amplification of the Azores in the western Atlantic.

Agree, been watching how ex-Gert interacts and in effect alters the Atlantic jet over last few days and certainly it is still causing some differences between GFS and EC ops and even the GEFS and EPS mean H500 flow as early as day 5-6.

Day 6 (t+144) GFS and EC H500/SLP ops

Day 6 (t+144) GEFS and EPS H500/SLP mean

00z GFS wants to track a break-away upper low / surface low with remnants of ex-Gert east across the UK next week, whilst EC keeps the low/ex Gert out west, as the W-E jet weakens, before the low dumbbells around the upper trough over the NW Atlantic and a ridge builds north further east and it warms up quite a bit across the UK next week as a result, especially the south.

Further along, 00z EC warms things up nicely toward / into last week of August, as another jet streak coming out of N America dives SE and carves out a trough to our west - which draws a plume of warm air north across western/central Europe.

However, wouldn't have much confidence atm past early next week, given the difference between GFS and ECM!

Edited August 18, 2017 by Nick F

[Man With Beard]

I'm guessing the complexities of modelling an ex-hurricane might be one instance where we might expect the op runs to lead the ensembles. This certainly appears to be the case with the ECM in the past 24 hours. Compare yesterday's clusters for T120 with today's T96. Yesterday, the op stalled the incoming low west, but appeared a bit of an outlier with little support in the clusters, but this morning the whole ensemble set moved towards it.

 

[Singularity]

   

Seems to me the impact of Gert has been enhanced by the relative position of the trough that it merges with to one at higher latitude. 

While we do see the advected warm airmass aloft leading to a ridge build ahead of it which GFS has been increasing with each new run (bringing it ever closer to the 00z ECM run), there's also a compact trough crossing Greenland which serves to shift the main path of the jet stream away from the trough containing Gert's remnants and so cause it to become cut-off from the main westerly flow. If we look at yesterday's 12z GFS with the faster ex-Gert-trough combined system, we see how it escaped this influence from the Greenland trough, with the ridge-building instead simply expanding the Azores High N/NE in a classic fashion.

Returning now - today's 12z GFS even sees the warm airmass wrapping around the low close to us encourage a northward arc of the jet around Iceland. The 00z ECM was very similar in this regard and by way of response developed a surface high to the NE of the UK that helped to keep the cut-off low stalled out west of the UK.

The 12z GFS has turned out similar to that ECM 00z, but without quite managing to fully shut down the west-east motion of the cut-off low. Typical of the model really. Then we see the next Atlantic trough disrupting against the block - again similar to that ECM run - and as such we find ourselves continuing to live out a warm but often unstable way of life.

 

This change of 'mode' could be enough to bring the mean August temps close to the long-term average for many parts - but this may be accompanied by some seriously large monthly rainfall totals given how wet it's already been in many places (even here in the far S. it's headed above average following thundery downpours today, having been right on it - literally 100% of the norm - up to yesterday).

Edited August 18, 2017 by Singularity

[mb018538]

Oh dear is all you can say....what looked like almost certain high pressure moving in a day or so ago now looks like we might end up with a trough once again. You have to laugh at our weather sometimes, truly pathetic.

[knocker]

An interesting feature of the ecm today is as our current  low moves into the North Sea a quite intense thundery feature, currently in SE France /Germany, is caught up the circulation of the low in the southern quadrant and tracks quickly north east and intensifies to be over norther Sweden by 18z tomorrow  Looks like some very interesting weather along it's track.

[The PIT]

Tonights ECM quickly brings back the Atlantic. At the moment it doesn't look we will get any real change in the pattern long term.

[mb018538]

ECM ends badly too, so we now have GFS, ecm and gem all showing trough dominated weather by day 10...whatever happened to the jet lifting north and things getting quieter?? Those bone dry GFS ensembles will be changing for sure. Let's just get to September and start autumn up now please!

[Frosty.]

ex Gert is going to help introduce warmer more humid tropical maritime air across the uk later in the weekend and even warmer during the first half of next week with very warm / humid  continental air pumping north across especially southern uk according to the Ecm 12z so at least as far as temperatures are concerned, a late taste of summery warmth looks to be on the way, especially where there is some sunshine with temps into the mid / upper 20's celsius in favoured parts of the s / e / se.

Edited August 18, 2017 by Frosty.

[knocker]

20 minutes ago, mb018538 said:

ECM ends badly too, so we now have GFS, ecm and gem all showing trough dominated weather by day 10...whatever happened to the jet lifting north and things getting quieter?? Those bone dry GFS ensembles will be changing for sure. Let's just get to September and start autumn up now please!

I'm not sure where the idea originated but looking at tonight's 300mb wind field shows Gert hitching a ride on the jet initially before disrupting it at the beginning of next week but by next weekend it is blowing quite strong roughly west- east again albeit with an interesting dip SE just to the west of the UK prior to this.

[ANYWEATHER]

Evening All , Despite a Dirty night outside , A Brucy bonus for the ecm  in the ten day period , gfs showing high pressure  and ecm showing much less settled weather. Not buying in to any model ouput  at the moment given the high level of Shannon Entropy due to the effect of Tropical Displacement , Fascinating viewing anywayNice to see you to see you nice .......

[mb018538]

BBC long range forecast tonight....sorry but where are they getting this from? There isn't any output supporting this!! 

[weatherguru14]

4 minutes ago, mb018538 said:

BBC long range forecast tonight....sorry but where are they getting this from? There isn't any output supporting this!! 

Its  Darren Bett,, its not the first time this summer he's done this..

[Man With Beard]

46 minutes ago, mb018538 said:

BBC long range forecast tonight....sorry but where are they getting this from? There isn't any output supporting this!! 

UKMO - was it this morning that it pulled out a massive UK high for later next week? Of course the ECM this morning was fairly anticyclonic. But seems a bit early to be forecasting next weekend given the serious problems in forecasting the depth and speed of exit from Gert. Various possibilities IMO.

[knocker]

At least last evening there was some conformity between the anomalies, certainly in the earlier period.

The key points of the pattern are low pressure over the Arctic (there has been a lot of that around this summer) centred near Russia with trough over Greenland and an associated trough SE of the latter to the UK and further south towards Iberia. Coupled with this some ridging from the Azores in mid Atlantic and some positive anomalies north of the UK.

This all boils down to quite a strong WNW upper flow in the western Atlantic which becomes very slack in the east where the influence of the trough and the HP to the north come into play.It would tend to indicate a slack area of low pressure over and in the vicinity of the UK which the det runs can have a great time sorting. It doesn't bode well temp wise but any detail vis the weather a complete lottery at this stage.

Further afield as the main trough over Greenland shifts orientation east and the positive anomalies to the north disappear a more consistent westerly upper flow becomes the order of the day and perhaps a continuation of the unsettled regime.

Back to this morning's gfs but first the weekend but first the weekend.

Today should see the frequent showers mainly around Wales, the Midlands and the north move away east during the day, leaving quite pleasant weather later, if a tad cool, which continues on into tomorrow albeit in the west the fronts from Gert will start to effect the south west and then move north during the day. The wetter weather should be confined to the west.

By Tuesday the rain is still effecting N.I and Scotland with Gert loitering out to the west and this continues into Wednesday which is a little unfortunate as elsewhere it is quite pleasantly dry and warm over these two days

By Thursday the low has moved east to be over the Hebrides and it has received a top up from the north west so two or three days of unsettled weather ensues as the surface low pressure area gets more organized and tracks across the UK into the North Sea. But as soon as this low clears the next quite deep low arrives to the NW and the associated fronts sweep across on Sunday. I don't think any of this is nailed down by a long chalk.

 

Edited August 19, 2017 by knocker

[knocker]

The ecm is also looking unsettled from Friday onwards (some transient ridging England and Wakes on Sunday) but it handles the next low to the NW somewhat differently to the gfs so the detail for next weekend is not as yet nailed down.

[mb018538]

You only have to scroll back one page to see that even 2 days ago on Thursday the ensembles painted a dry picture, the UKMO had a big anticyclone moving in by Wednesday next week, and the noaa anomalies were all showing high pressure.

Yet another forecasting bust, which goes to show even ensemble clustering etc can be completely wrong at times. Back to square one again it seems, with the buckled jet taking no time at all to fire back up on it's now normal W-E southerly trajectory.