Model Output Discussion - Mid Summer Onwards

[Cambrian]

Two standout seasonal features of the Northern Hemisphere weather in the week running up to and through the autumn equinox to be seen in the 0z ECM operational run.

The first is an injection of energy into the Atlantic jet stream, any straggling remnants of meridional pattern quickly swept away. Two pulses originating to the south of Greenland over the next few days. The first clears out the meridional pattern at the ruck and the second bursts down the middle spreading it left on the loop. A nice looking move, the jet stream running to the south for a while around day 6, oscillating north-south thereafter, with a further pulse of energy charging through the UK and Ireland by day 9.

 

No return of an Atlantic meridional pattern, though there is on the Pacific side for a while, south of the Bering Sea between days 4 and 6. This too gets pushed along, with the ribbon passing all the way through Canada by day 9. We haven’t seen that in a while, indicative of a somewhat more mobile phase. 

There is something aesthetically satisfying about watching the movement of the low pressures that the jet stream is directing, the first pulse directing the movement southeast from Greenland to the north of Scotland, the second picking up ex-hurricane Lee, passing it to the first low, that swings it down through the mid Atlantic, to bring the remnants of Lee through the UK and Ireland by the end of the week at day 6. 

 

A long way off, but the result of the modelled strengthening of the jet stream through our neck of the woods around day 9 is the deepening of the low between Iceland and Scotland to around 955mb. 

The second seasonal feature is the cooling of the polar region, shown here by the T850s, a clear and steady build through the park in general, with the occasional offload in our direction. 

  

At day 1, the zero degree isotherm being kept tight in the early stages. There’s the quick little offload from the passing Lee at 180h, bringing the UK and Ireland into the move. By day 10, the pack is doing its job, digging deep, -18 to -20 degrees over northeastern parts of Greenland, and as the opposition tires, the opportunity for a more expansive game going forward. 

[Penguin16]

5 hours ago, Blessed Weather said:

Aren't those charts in km/h?  Converted to mp/h would mean a peak gust of 81 mp/h which, yes, is windy but more in line with typical UK gales?

211 km/h = 131mph ,30 miles off the coast of Ireland before heading on to NW Scotland but weakening before that.

[damianslaw]

UKMO, ECM and GFS all closely aligned in the short-medium term, i.e. out to day 6.

Low pressure in the ascendancy.. swinging in from the NW early next week and pushes east out to the N Sea by Friday.

End result, a cooling for all early next week, with wind and rain moving through the UK. Heaviest rain and strongest winds in the north and west.

A bit of uncertainty thereafter, ECM keen on another low pressure quickly impacting next weekend. GFS at variance with suggestion of heights building in from the SW holding atlantic at bay.

The jetstream does appear to be getting a bit of oomph to it on a more typical westerly trajectory. Autumnal conditions arriving in time for the equinox. 

[Metwatch]

Interesting to see the GFS and quite a few of its ensembles going for something more settled towards the end of the month. ECM ens showing something similar as well. I think the chance of a settled period to end this month doesn't seem high though.

It has been a good while since we've had a settled end to September. I don't imagine it would be particularly very warm by the end of the month either if the winds did start to come from more of an easterly - south easterly direction, sourced from the near continent.

The only way to really get high 20s by end of September / early October is a longer fetched southerly with no inversions / cooler air trapped close to the surface (1985 and 2011, 2 recent examples of very warm late Sept / early Oct surface temperatures).

[Mike Poole]

Looking a bit further ahead of an unsettled week next week, the ECM clusters have this at T192-T240:

Cluster 1 here with 34 members heralds a return to warmer and more settled weather, whereas cluster 2 with 17 members stays unsettled.

T264+:

Clusters 1 and 2 (totalling 36 members) continue towards something settled for the last week in September, not so cluster 3.  The regimes plot still shows a signal for blocking over Scandi (red) once the unsettled Atlantic spell (blue) is done, so I would expect the overall CET for September to be very high when the month is done and dusted, be interesting to see if any records are broken there.

Would you Adam and Eve it, apparently I’ve been a Netweather member for 10 years!  Just want to take the opportunity to say a big ‘thanks’ to everyone who posts here, I have learned so much about all aspects of the weather from the contributions from everyone, it is a great community to be a part of.  

Here’s to the next 10 years, all the very best.

Mike

 

[Crackerjack]

16 minutes ago, Mike Poole said:

Looking a bit further ahead of an unsettled week next week, the ECM clusters have this at T192-T240:

Cluster 1 here with 34 members heralds a return to warmer and more settled weather, whereas cluster 2 with 17 members stays unsettled.

T264+:

Clusters 1 and 2 (totalling 36 members) continue towards something settled for the last week in September, not so cluster 3.  The regimes plot still shows a signal for blocking over Scandi (red) once the unsettled Atlantic spell (blue) is done, so I would expect the overall CET for September to be very high when the month is done and dusted, be interesting to see if any records are broken there.

Would you Adam and Eve it, apparently I’ve been a Netweather member for 10 years!  Just want to take the opportunity to say a big ‘thanks’ to everyone who posts here, I have learned so much about all aspects of the weather from the contributions from everyone, it is a great community to be a part of.  

Here’s to the next 10 years, all the very best.

Mike

 

Thanks Mike and congratulations mate. You are one of my go to posts and have been for a long while, always concise and well written thoughts that makes it easier for a novice like me to read and understand

[northwestsnow]

Hope we get a settled end of Sept some lovely walking weather and nature at its finest this time of year.

EC says maybe....

 

[Captain Shortwave]

The long wave pattern for week 2 seems to be heading towards Atlantic trough/strong Euro high. We shouldn’t rule out the chance of some very warm conditions occurring at the end of the month.

ECM day 7

 

GFS/GEM

   
 

Pretty good agreement for that Atlantic low to throw up a ridge ahead of it. Can we get the amplification to veer the winds southerly rather than a broad south west flow.

[Sun Chaser]

GFS consistently throwing some nice warm temperatures in the hat for the end of September now. With this ridge to the east and a trough to the west setup the models seem to be sniffing out, summer might not be done with us just yet

Is mid twenties possible in the final week of the month?

[Cambrian]

This is great stuff. If heights do rise over Western Europe during the last few days of the month, it’s hats off to the ECM extended range forecasts. These are the charts from 8 September for the 18th to 25th September and 25th September - 2nd October, week 2 and week 3 at the time. I posted them back then along with the suggestion that taken at face value, the trend raised the possibility of a better end to the month as tropical storms stall in the Atlantic, pumping up a ridge over Europe. 

 

Here are yesterday’s ECM46 charts for the same weeks, now the coming week and week 2.

 

Though the heights rises aren’t in exactly the same places, the broad profile is the same, good heights over Europe, eastern parts of North America and Greenland, low heights over the Atlantic and the Western US.

Still in the centre circle with the MJO, but hints of a match with the September composite for phase 1 (at least for our neck of the woods!) in the coming week, so it might be showing signs of working its way back through the CoD in that general direction. 

  

The October MJO Phase 1 composite (right) would fit with the heights rises over Western Europe as we move from September to October and also sits fairly well alongside the 0z ECM and GFS day 10 mean anomalies as we head towards the beginning of October…

 

- heights to the southeast over the continent, the heights over Greenland receding but staying strong over eastern parts of North America, lower heights maintained over the Western US and Atlantic, and the UK and Ireland in a marginal zone, with occasional Atlantic incursions vying with resilient European heights, temperatures just above average with a flow generally from a quadrant between south and west. Have a great day. 

Congratulations to @Mike Poole for the 10-year milestone. I greatly enjoy your contributions.

[legion_quest]

The ECM trying to find that heat, but I'm going to stick with the Jet Stream forecasts and the strengthening polar vortex in the charts at the top of the page keeping the heat pushed back.

Mainly because that's what I want, but hey, doesn't hurt to 'pick a side!'

[Mike Poole]

ECM clusters this morning continues to support a warmer spell days 8-10.

Consistent across them is the wind from a southwesterly quarter, it seems that there will be a NW/SE split in terms of how settled the weather is depending on the strength of the block to the east.  Cluster 1 has it weakest (more westerly winds), cluster 3 strongest, and cluster 2 in the middle.  

[Tamara]

6 hours ago, Sun Chaser said:

GFS consistently throwing some nice warm temperatures in the hat for the end of September now. With this ridge to the east and a trough to the west setup the models seem to be sniffing out, summer might not be done with us just yet

Is mid twenties possible in the final week of the month?

Boa tarde

Its almost certain to be over 30C down here in Portugal to see out the month & I think, yes. the mid 20s is certainly possible to bookend a quite remarkable month for the UK

Usual emphasis on some of this thread on MJO composites alone, but without considering the extra tropical GWO circulation (which is also fully alight with tropical activity) then the full story is not told.

Something of a repeat of early September looks to be in the offing, albeit with an increasing temperature gradient across N Europe this time, which is likely to hinder the full omega block pattern that lead to the longevity of that amazing heatwave.

Notwithstanding that, a similarity still revolves around another boost to angular momentum tendency as further momentum transport propagates from the tropics c/o convection returning into the Pacific & imprinting the Nino standing wave which continues to expand westwards across the ENSO region. This, taking the Global Wind Oscillation out of its doldrums and creating a more harmonious wind-flow signal with the MJO in the tropics that likely means a stronger signal than represented by the MJO alone. However, it is also the movement of ex tropical Nigel that looks to coincide within the framework of this rising AAM tendency. Creating some further extra amplification on top of the tropical>extra tropical wave-breaking to offset a more volatile jet stream than was present earlier in the month.

The net result should be enough to amplify the Atlantic profile sufficiently to take Nigel far enough west (!) of North Western Europe  - sharpening the downstream ridge extending from the Azores and pulling up air from my part of the world that is set to embark on a late heat up from next weekend. Mainland continental Europe looks to benefit from this first of all. How much of the UK might be influenced from the advection of this heat is uncertain, but latest NWP trends seem to be adjusting away from the flatter pattern advertised yesterday.

Boa sorte.

 

Edited September 17, 2023 by Tamara

[Kirkcaldy Weather]

On 14/09/2023 at 16:54, Downburst said:

That's strange as the US professionals use the ECMWF because it is more accurate.

Hey @Downburst I was gonna adress this anyway and happened to see your post first. The EC was overall poor with the handling of Idalia and similarly erroneous on Lee in both track and particularly in regards to RI and overall cyclogenisis strength.

We see the UKMET AND EC were churning out overall high amounts of erroneous data for Lee whereas the GFS shown as AVNO was steadfast with a brilliant accuracy level even from +5 days in advance.

My view would be continue to have the highest trust in the GFS plus GEFS GEPS 

Here's the evolution from Now through Midweek - Thursday

On 14/09/2023 at 15:36, Kirkcaldy Weather said:

Developing trough meanders from Northwest Spain toward the Portugese border

First there is energy separation within said trough which leads to a low developing here in Fife

 

 

As the energy and development of this low increase into the overnight hours tonight this will see a rapid increase of precip rates within a front focusing in on West-Northern and Northwest Scotland. There will be a separate area seeing formation of thundery cells especially through SE England into East Anglia (same timing) this area I'd put within

 Medium Impacts

For the Scottish area mentioned I'd give at least medium but could extend to

 Severe Impacts

Lower probability with gusts but if the low deepens sufficiently increasing gusts in Southwest Scotland towards the Northeast corner could occur. 

And I am EXTREMELY concerned with the impacts occuring over a wide part of Scandi from Mid Monday but biggest worry is Kristiansand up to Grovane>Birkeland. 

️EXTREME Impacts

Slight breather during Tuesday but the next concerns arise for Wednesday and Thursday.

I've highlighted the development zones as energies from Greenland, Lee and a smidge of Margots energy all combine 

Fine details will become clear probably by Tuesday but the statement I made within my previous post very much coming to fruition 

'Into mid and latter Sept we need to be alert for impacts being heightened especially as Lee + Margot will be morphing and increased Jet Streak action begins'

Initial wind threat starts to appear and the Jet Streak

Main rain zones with this Weds Thursday development currently same areas as tonight for Scotland ie Northwest... Western... plus Northwest England, Wales and an interesting signal running across Southern England though not all data supports the latter just yet 

 

[Polar Maritime]

Let's keep posts friendly... At the moment this is, and has been for a good while a relaxed Model discussion thread, Some people like what others don't and hope for. It would be nice for it to continue like that before the (mad) season starts... That's when the team have to start fine tuning the thread to keep it running smoothly. Just like we have to do during the end of Winter when Spring is on the way.

We certainly don't won't to be doing that just yet! The turn-over of the seasons from Summer to Winter and vice-versa always brings with it the problems/emotions of what members want/don't want when on the crusp of the change of seasons. It's the same every year from one end to the other... Remember we are all in together no matter what ones preference is.

Thanks all 

Edited September 17, 2023 by Polar Maritime

[Mark wheeler]

Nice GFS later in the run this evening.

 

meanwhile gem wants to go up a level .

Edited September 17, 2023 by Mark wheeler

[Penguin16]

In my opinion the high will be further south and conditions much more unsettled that currently pronged for that time frame. 

Edited September 17, 2023 by Penguin16

[Polar Maritime]

6 minutes ago, Penguin16 said:

In my opinion the high will be further south and conditions much more unsettled that currently pronged for that time frame. 

Do any models show this yet? Certainly not out of the question though re-your thoughts. It will be interesting how how the models handle the questioned Low coming in off the Atlantic. Early days yet so best to keep an open mind atm

[Metwatch]

October 2011 repeat anyone if the GEM is to go by?

Looks like the consensus is gaining momentum for a late September settled spell, a great time for high pressure in my opinion I think when you get mist and fog at morning, then warmth by day with the weakening sunshine. Crisp sunny days under the orange colours, perfection!

Edited September 17, 2023 by Metwatch

[Addicks Fan 1981]

6 hours ago, legion_quest said:

The ECM trying to find that heat, but I'm going to stick with the Jet Stream forecasts and the strengthening polar vortex in the charts at the top of the page keeping the heat pushed back.

Mainly because that's what I want, but hey, doesn't hurt to 'pick a side!'

Think the anomoly charts @johnholmesposts are pretty good and the jet stream forecasts change all of the time.   Using the mean charts is better than looking at a rogue op run.    The ECM clusters as Mike Poole posted are a very reliable guide too.   

[Addicks Fan 1981]

23 minutes ago, Polar Maritime said:

Do any models show this yet? Certainly not out of the question though re-your thoughts. It will be interesting how how the models handle the questioned Low coming in off the Atlantic. Early days yet so best to keep an open mind atm

Absolutely, it's great to be objective rather than posting gut instincts with what maybe the case.   

[legion_quest]

I'd really rather not have another blast of Southern, humid air. 

Going to continue to hope that the Jet drops and takes the ECM by surprise. I do think it's modelling based on what just happened, rather than what will happen, and there are still too many things between then and now that can impact on it being settled or not.

But I also accept I'm definitely hope casting! 

[Cambrian]

It can be all too easy to take affront. So how about two fronts? And twice in three days? Most in the UK and Ireland will see exactly that through to midweek as two pairs of fronts, each tending to merge into one belt of rain, pass through on Monday and Wednesday, as shown in the 0z UKMO fax charts and the 12z GFS op precipitation charts:

0z fax for 12z on Monday, the GFS from this evening at 6h, showing the belt passing through Ireland this evening, into Wales and Scotland during the morning fragmenting as it passes east through England later tomorrow, clearing away by late on, at 33h. 

 

0z fax for 0z and 12z Wednesday, GFS showing the rain into Ireland and Scotland by Tuesday evening at 57h, clearing through all parts by Thursday morning at 93h. With lower pressure around, this one doesn’t fragment as it moves southeast, indeed quite the opposite. There is a wave running along the second front, visible on the fax and nicely picked up on the GFS too, that delivers an extra pulse of heavy rain as it passes through central and southeastern parts of England during Wednesday night and the early hours of Thursday.

   

Some good totals building - two inches of rain by 96h for parts of Ireland, Wales and England, including parts of the south and southeast, even more for parts of Scotland, with more rain to come for all later in the week, before a likely improvement in the last week of the month. 

Edited September 17, 2023 by Cambrian

[carinthian]

3 hours ago, Tamara said:

Boa tarde

Its almost certain to be over 30C down here in Portugal to see out the month & I think, yes. the mid 20s is certainly possible to bookend a quite remarkable month for the UK

Usual emphasis on some of this thread on MJO composites alone, but without considering the extra tropical GWO circulation (which is also fully alight with tropical activity) then the full story is not told.

Something of a repeat of early September looks to be in the offing, albeit with an increasing temperature gradient across N Europe this time, which is likely to hinder the full omega block pattern that lead to the longevity of that amazing heatwave.

Notwithstanding that, a similarity still revolves around another boost to angular momentum tendency as further momentum transport propagates from the tropics c/o convection returning into the Pacific & imprinting the Nino standing wave which continues to expand westwards across the ENSO region. This, taking the Global Wind Oscillation out of its doldrums and creating a more harmonious wind-flow signal with the MJO in the tropics that likely means a stronger signal than represented by the MJO alone. However, it is also the movement of ex tropical Nigel that looks to coincide within the framework of this rising AAM tendency. Creating some further extra amplification on top of the tropical>extra tropical wave-breaking to offset a more volatile jet stream than was present earlier in the month.

The net result should be enough to amplify the Atlantic profile sufficiently to take Nigel far enough west (!) of North Western Europe  - sharpening the downstream ridge extending from the Azores and pulling up air from my part of the world that is set to embark on a late heat up from next weekend. Mainland continental Europe looks to benefit from this first of all. How much of the UK might be influenced from the advection of this heat is uncertain, but latest NWP trends seem to be adjusting away from the flatter pattern advertised yesterday.

Boa sorte.

 

Just a remarkable  September in these parts ( Eastern Alps ) I have been here since 2005 and have never known such a warm sunny September. Looking at the models, looks like more of the same and I am sure  by months end all records will be broken . Not just day time max but night mins. Currently 17c in the village at 1450m absl, Thats crazy for Mid - September. Not sure whether all of The British Isles will tap into some of the late September continental heat but I am confident that the south will see some renewed advection at times from that souce.

C

[Mark wheeler]

Yes please ECM