Model Output Discussion - Into Autumn 2020.

[sheikhy]

And the settled weather continues for the forseeable future on ukmo and gfs!!over to the ecm to complete the hattrick!!

[Gowon]

Not UK weather, but the GEM and Icon develop a storm in the Med on Wednesday heading towards Greece.

I don't think I've ever seen a storm like that in the Med?

 

[NApplewhite]

3 minutes ago, D.V.R said:

Not UK weather, but the GEM and Icon develop a storm in the Med on Wednesday heading towards Greece.

I don't think I've ever seen a storm like that in the Med?

 

The storm is off the SW coast of Italy but i've checked the weather for Corfu for Wednesday and temps are 36 degrees with long sunny periods so i don't know where its heading.

[NApplewhite]

32 minutes ago, sheikhy said:

And the settled weather continues for the forseeable future on ukmo and gfs!!over to the ecm to complete the hattrick!!

Looking good! no sign of rain in England and Wales for a long time! Perhaps we are heading towards a drought! please let us have a dry hot autumn .  

Spoke too soon - some rain in the forecast for Sunday and 30% risk of Rain on the 26th September in Northern England according to the models  

Edited September 14, 2020 by NApplewhite
Ame

[Gowon]

7 minutes ago, NApplewhite said:

The storm is off the SW coast of Italy but i've checked the weather for Corfu for Wednesday and temps are 36 degrees with long sunny periods so i don't know where its heading.

If the two models are right, it won't hit Greece until Thursday night onwards.

 

[mb018538]

16 minutes ago, D.V.R said:

Not UK weather, but the GEM and Icon develop a storm in the Med on Wednesday heading towards Greece.

I don't think I've ever seen a storm like that in the Med?

 

It’s not too unusual - they are called ‘Medicanes’ and display some similar characteristics to hurricanes, though aren’t classified as such.

[Frosty.]

If you like high pressure, bank the Ukmo 12h!...As for the GEFS 12z mean, well, it’s hard to believe it’s mid September looking at tomorrow’s charts..SENSATIONAL!!! for the s / se!!..and plenty of high pressure to come for the rest of this week & well into next week and warming up again!

Edited September 14, 2020 by Jon Snow

[NApplewhite]

32 minutes ago, Jon Snow said:

If you like high pressure, bank the Ukmo 12h!...As for the GEFS 12z mean, well, it’s hard to believe it’s mid September looking at tomorrow’s charts..SENSATIONAL!!! for the s / se!!..and plenty of high pressure to come for the rest of this week & well into next week and warming up again!

Any snow on the horizon ?? 

[Frosty.]

1 hour ago, NApplewhite said:

Any snow on the horizon ?? 

FI looks interesting   

[Mair Snaw]

20 minutes ago, Jon Snow said:

FI looks interesting  

Those uppers look a bit marginal..

[Allseasons-Si]

Someone calm me down!!!

[Man With Beard]

Well those charts above are pretty much the "polar opposite" of what we have right now...

Can we achieve surely the only ever year with 90F recorded in 4 separate months? Tomorrow is the big chance. AROME going for 31C, ARPEGE 32C but in Kent rather than London, so may suffer for lack of reporting stations. If only Gravesend was still running!

[Relativistic]

26 minutes ago, Man With Beard said:

Well those charts above are pretty much the "polar opposite" of what we have right now...

Can we achieve surely the only ever year with 90F recorded in 4 separate months? Tomorrow is the big chance. AROME going for 31C, ARPEGE 32C but in Kent rather than London, so may suffer for lack of reporting stations. If only Gravesend was still running!

Has happened a number of times before. See this post in the Autumn thread:

 

[Cheshire Freeze]

2 hours ago, Allseasons-si said:

Someone calm me down!!!

What a stunning chart!

[NApplewhite]

10 hours ago, NApplewhite said:

Any snow on the horizon ?? 

Settled into the end of the month apart from a few small blips - FL I KNOW! Next Tuesday expect cold wind and rain.    Storms heading our way from the Atlantic  - Ex Hurricane Sally perhaps? 

Edited September 15, 2020 by NApplewhite
Add Hurricane Sally discussion

[NApplewhite]

Hurricane Sally Discussion Number 15 NWS National Hurricane Center Miami FL AL192020 1000 PM CDT Mon Sep 14 2020 After rapidly strengthening earlier today, Sally's intensity has plateaued for now. Both the NOAA and Air Force Hurricane Hunters have been investigating Sally this evening and they have found that the minimum pressure and winds have leveled off, and support perhaps a generous initial intensity of 85 kt. Doppler radar images and reports from both aircraft indicate the inner core of the hurricane is quite small and that the eyewall is open on the south side, likely due to some dry air that has wrapped into that portion of the circulation. Aircraft and Doppler radar fixes indicate that Sally is moving very slowly to the west-northwest, with the latest initial motion estimated to be 300/3 kt. Weak high pressure ridging to the north and east of Sally is expected to cause the hurricane to continue to move slowly west-northwestward to northwestward for another 12 hours, bringing the center of the storm very near the northern Gulf coast. By Tuesday afternoon, when the hurricane will likely be just offshore, the models show the steering currents collapsing and Sally is likely to drift northward before finally turning northeastward ahead of a developing mid-level trough over the central U.S. by late Wednesday. There continues to be a significant amount of uncertainty on exactly where and when Sally turns northward and makes landfall, with model solutions ranging from a landfall on the Florida panhandle to a landfall in extreme southeastern Louisiana. It should be emphasized that it is always challenging to forecast the track of hurricanes in weak steering currents, and in Sally's case the weak steering is occurring very near land.

The new NHC track forecast is a little to the east of the previous one, trending toward the latest consensus aids. Sally is still in generally favorable environmental conditions consisting of very warm SSTs and low wind shear. Since the hurricane will likely remain in those conditions through Tuesday morning, some strengthening seems likely in the short term. In 12 to 24 hours, when Sally is forecast to be very near the coast, a combination of an increase in westerly shear and cooler upwelled shelf waters should limit additional intensification. After the hurricane makes landfall, rapid weakening is forecast and Sally should become post-tropical in 3 to 4 days over the southeast U.S. The NHC intensity forecast lies at the high end of the model guidance and is quite similar to the previous one. Users are reminded to not focus on the exact forecast track or the specific timing and location of landfall. Hurricane-force winds, dangerous storm surge, and flooding rainfall will affect a large portion of the north-central Gulf Coast during the next few days. KEY MESSAGES: 1. It is still too early to determine where Sally's center will move onshore given the uncertainty in the timing and location of Sally's northward turn near the central Gulf Coast. Users should not focus on the details of the official forecast track, since NHC's average forecast error at 36 hours is around 60 miles, and dangerous storm surge, rainfall, and wind hazards will extend well away from the center. 2. An extremely dangerous and life-threatening storm surge is expected for areas outside the southeastern Louisiana Hurricane and Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to the Okaloosa/Walton County Line in the Florida Panhandle, where a Storm Surge Warning is in effect. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are expected early Tuesday within the Hurricane Warning area in southeastern Louisiana and are expected by late Tuesday and Tuesday night within the Hurricane Warning area along the Mississippi and Alabama coastlines and the western Florida Panhandle. Tropical storm conditions are already occurring in some of these areas. 4. Life-threatening flash flooding is likely with Sally, as well as widespread minor to isolated major flooding on area rivers, along and just inland of the Central Gulf Coast. Significant flash and urban flooding, as well as widespread minor to moderate river flooding is likely across inland portions of Mississippi and Alabama and into northern Georgia, southeastern Tennessee and the western Carolinas through the week. Sally may continue to produce flash flooding across the Florida peninsula and prolong existing minor river flooding across west-central Florida through tonight.

FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 28.9N 87.6W 85 KT 100 MPH 12H 15/1200Z 29.1N 88.1W 95 KT 110 MPH 24H 16/0000Z 29.6N 88.4W 90 KT 105 MPH 36H 16/1200Z 30.4N 88.3W 85 KT 100 MPH...INLAND 48H 17/0000Z 31.3N 87.4W 50 KT 60 MPH...INLAND 60H 17/1200Z 32.0N 86.3W 30 KT 35 MPH...INLAND 72H 18/0000Z 32.7N 84.9W 25 KT 30 MPH...INLAND 96H 19/0000Z 33.1N 82.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 20/0000Z...DISSIPATED $$ Forecaster  Cangialosi 

Edited September 15, 2020 by NApplewhite

[sheikhy]

And finally it looks like this dry spell is coming to an end in a weeks time according to ecm!!ukmo looks the outlier but has been the most consistant so not ignoring it just yet!!gfs somewhere inbetween!!

[I remember Atlantic 252]

1 minute ago, sheikhy said:

And finally it looks like this dry spell is coming to an end in a weeks time according to ecm!!ukmo looks the outlier but has been the most consistant so not ignoring it just yet!!gfs somewhere inbetween!!

GFS looks pants after today, 16 degrees and breezy, and no doubt thick misty low cloud

[mb018538]

1 minute ago, sheikhy said:

And finally it looks like this dry spell is coming to an end in a weeks time according to ecm!!ukmo looks the outlier but has been the most consistant so not ignoring it just yet!!gfs somewhere inbetween!!

Could just be a blip @sheikhy !



Looks like a slightly more unsettled spell by the middle of next week, but generally the main storm track looks like staying to the NW of the UK after:



Could be your traditional NW/SE split towards the end of the month. With AAM staying relatively high, i don't see any plunge into full-on zonal trash here just for now:

[mb018538]

ECM losing the plot at day 7-10 today, far too unsettled. How quick can the recovery come after? Tropics all ablaze with storms and hurricanes, so i'm going to stick with a reasonable-ish outlook beyond the middle of next week, with the chance of some unexpected twists and turns to come!

[MATTWOLVES 3]

Hope your all well folks... Last night's EC46 keeps with the settled theme for the next week.. Later next week perhaps a more NW/SE split devoloping. Towards the months end we still have High Pressure Influence for more Southern parts, but perhaps more unsettled further North at times.. Moving into October the general theme of ridging at times for many parts, so still a chance of plenty of fine and settled conditions at times. It's not until the final 3rd of next month that things eventually become much more unsettled from the the NW.. I'm sure many would take that outcome considering all the current uncertainties around the world.. That's how it looks right now.... Enjoy the fine weather if you can. 

All the best... Matt

 

[Tamara]

Posted August 29 (edited)

What of the change of month and the previous suggestions of improved warmer weather once again ?    Still on cue whatever numerical operational model vicissitudes appear to indicate - albeit as per the theme of the beginning of this post, never a straightforward process at this junction of the Northern Hemisphere.

As was the case in late July and early this month, the high frequency MJO signal has growing confidence to embark on another eastward progression across the topics, much as discussed in detail in previous posts. The cue to promote attempts at further downstream ridging.  Deterministic RMM modelling between the ECM and GFS is coming together with this trend, but this less reliable MJO modelling in terms of suggested amplitude path is very open to further forecast adjustment (i.e on the upside)

At present NWP is very keen to retain an element of a more dominant Atlantic ridge and  the tendency to allow fronts to slip south as pressure falls ahead of it  sometime around next weekend.  Some caution is required in the coming days as to whether or not any further retrogressive Atlantic ridge signal is overdone or not beyond this time - not so much as to how it evolves at face value - but more in terms of how the longer term pans out. 

The lessons from late July and the obfuscated lead up to when the intense heatwave suddenly started to appear in numerical modelling were that these same numerical models were, as anticipated back then,  too blindsided by the low frequency upstream signal and made late adjustments to over progressive inroads on cold fronts and return of cool North Atlantic air, due to over amplifying the incoming Atlantic ridge to the west of the UK, and therefore digging the polar front too far south.  The reality was that downstream ridging across Europe and Scandinavia proved more resistant than advertised and the subsequent heat dome persisted for much longer than initially suggested

This time around, there is clearly not going to be anything close to any extent of advected heat source later this week. However, irrespective of this, based on the suggestion of an amplitude MJO wave progressing right into the Pacific through September, this ultimately supports the sort of de-amplification upstream (and subsequent downstream amplification in this neck of the woods) that happened in early August. On this basis there is support for the idea of any renewed ridging coming in from the west, adjusting itself eastwards to become positioned to the east and drawing a plume of very warm air from southern europe and up through France and to knock on the door of the UK.

It is more a question of timing of this, rather than if it happens at all. I am, as ever, suspicious and questioning of NWP trends and do not take each and every output at face value.

The ideas behind any further plume potential lie beyond  next weekends proceedings and based on the movements of the renewed ridge  advancing eastwards into the following week. This rather than trying to retract the high westwards and lower pressure again across the UK and other parts of NW Europe.

It seems counter intuitive to expect further retrogressive flow after next weekend when the tropical signal supports increased momentum upstream in the longer term. 

So, and for what it is worth as I do not profess at all to be a "forecaster" as such and rather simply look at diagnostic probabilities -,  it may take some time to benefit areas further north and west, but the evolution of ridging may ultimately manifest itself as stretched between the European mainland, the UK and with some slight and very subtle discontinuous retrogression to the Azores/Atlantic high pressure zone. But not too much discontinuous retrogression to allow pressure to fall too much ahead of it across NW Europe.

Bias susceptibility to too much Pacific amplification possibly an element with this within some numerical products and it is on this basis to not be overly distracted by operational output but monitor the trends on numerical models c/o the ensemble means and clusters. This over a day or two at a time, rather than draw instant conclusions from each and every suite.

A very conducive outcome remains possible for some calm, warm and sunny September weather and evenings still warm enough for sitting outside with the lanterns and tea lights glowing in the now darker evenings than were enjoyed during the previous summer type spell of weather 

Edited August 29 by Tamara

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The above lengthy extract from a detailed analysis post towards the end of August requires little apology for re-posting because the evolution of the pattern has duly exposed the suspicions surrounding NWP that were expressed on this, and other occasions, around that period of time. The many various bolded parts are especially prescient.

So, beautiful summer-like weather is here to cherish for early autumn   Those tea-lights flickering gentle shadows in the darker evenings, as suggested to come in the bolded post,  being the one key difference as a reminder to the change of season since that early to mid August spell of classic summer weather

The 90 day Global Wind Oscillation plot, a phase plot depiction of global wind-flow inertia, tells the full story of the summer pattern and the quite clear departure from the default pattern during August as the GWO reflected a higher angular momentum regime away the tight orbiting of from the low momentum La Nina phases 1 and 2 during much of June and July - returning once more to a low angular momentum regime in late August..

Namely, a switch during early August to anticyclonic wave-breaking downstream across NW Europe as the Pacific pattern switched to a less amplified signature and re-configured the downstream pattern - as the rossby wavelength switched downstream accordingly

Now, heading into the middle of September, we see a further downstream anticyclonic phase occurring at the time that, once again, rising relative angular momentum rallies the GWO orbits out of the lowest momentum phases and traces an orbit path along the lines of what was in progress at the beginning of August -  on the cusp of higher momentum GWO phase 4.  Though, important to note, this is based on a two day consolidated lag to Sunday 13th. and doesn't include latest developments subject to forthcoming update.

 

What of the outlook?

As everyone knows, further glorious weather to come through to the weekend itself (though of course regional variations with the easterly winds). Beyond that is another period of suspicion as to how keen NWP is to re-introduce the return of the trough digging as far south as it suggests.  Is numerical modelling, once again, far too fast in wanting to overdo the return of influence of the La Nina walker circulation?

Further out still - If the high frequency tropical convection stays active, does not slip into the doldrums, and continues to shake up the rossby wavelengths, then it will remain possible deep into autumn to see a continued variable mixed meridional theme that sees more departures from the typical Nina-esque Atlantic ridge and downstream trough. 

 Should the high frequency tropical signal weaken , then the walker cell will fully prevail and strengthen La Nina considerably and the pattern quite possibly becomes a little more predictable in terms of the pattern wavelength, I would think, for those who , unlike me, are forecasters . At least as far as it is possible to make suggestions as to how patterns may pan out in a world of long term and unpredictable climate shift.

In this scenario, the Atlantic ridge is suggested to increasingly be in charge with less interruption - and lead to a fair amount of polar maritime influences as this season progresses, for north western parts of Europe at least. The wavelength then looking to adjust the position and amplification of this ridge thereafter - with a flatter regime flowing around the perimeter of the ridging and ensuing in tandem with the more organised polar vortex. Therefore much depends on the character of this La Nina - whether it follows a 2017/2018 more east based nature, or whether it is the more familiarly seen (basin wide) traditional type. 

For me, I will have long completed my posting on this thread by such a time anyway - until next Spring. All being well and fingers crossed, I am by this time 1250 miles further south to escape the British winter. From a completely different perspective to the vast majority in the UK,  it will be be very interesting to see how a first winters weather pans out,1250 miles further south and with that, another highly fascinating learning curve to experience and enjoy  

 

 

 

[Downburst]

Well Tamara, it's unique to this part of the world that one would wish to travel 1250 miles south to escape the weather, only to have positive expectations about the fact that at least you can still talk about it. We are very affected and effected by the weather, no one can argue that  Come on autumn, what have you got next!

[sebastiaan1973]

Thanks Tamara for your effort to inform us. Where can we find actual information about the high frequency tropical convection in the tropics? 

Your story reminds me, of this article.

https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.2910

Edited September 15, 2020 by sebastiaan1973

[Methuselah]

Many thanks @Tamara, I hope all goes well for you in Portugal. You'll probs get as much snow this winter as will I!?