Model output discussion - summer rolls on

[Frosty.]

Longer term tonight's Ecm 12z ensemble mean looks increasingly settled, like the operational.☺

Edited September 13, 2018 by Frosty.

[Newberryone]

I think it’s fair to say one can deduce from tonight’s charts is that Helene is definitely going to have far less of an impact early next week than originally thought with heights to the south weakening the system well in advance. Furthermore, anyone hoping for something really more autumnal may have to be very patient as tonight’s longer term prospects scream “Indian Summer” 

[DR(S)NO]

14 minutes ago, Newberryone said:

I think it’s fair to say one can deduce from tonight’s charts is that Helene is definitely going to have far less of an impact early next week than originally thought with heights to the south weakening the system well in advance. Furthermore, anyone hoping for something really more autumnal may have to be very patient as tonight’s longer term prospects scream “Indian Summer” 

No offence intended Newberryone but your saying ‘Indian Summer’ yet earlier today there were posts of ‘ low after low’....

whats changed or what makes tonight’s charts more reliable?

[Scorcher]

7 minutes ago, DR(S)NO said:

No offence intended Newberryone but your saying ‘Indian Summer’ yet earlier today there were posts of ‘ low after low’....

whats changed or what makes tonight’s charts more reliable?

That has never been the case- which charts were you looking at or perhaps more accurately, whose posts were you reading? Next week has been looking warm for a few days now- the difference today is that the incoming storm is being shown further west with no direct hit for most of us. There have been hints of a pressure build afterwards for a couple of days at least. 

[JBMWeatherForever]

Helene still looks strong to me when it hits the UK as an x tropical storm next week. The track currently shown by the National hurricane centre takes it right into western parts. Still one to watch closely !

[Paul_1978]

10 hours ago, Scorcher said:

That has never been the case- which charts were you looking at or perhaps more accurately, whose posts were you reading? Next week has been looking warm for a few days now- the difference today is that the incoming storm is being shown further west with no direct hit for most of us. There have been hints of a pressure build afterwards for a couple of days at least. 

This one Scorcher.

[mb018538]

I did comment immediately below that post saying that yesterdays 00z was an outlier and not in keeping with the rest of the model guidance...

Nothing much has changed overnight....still looking at high pressure moving in late next week/next weekend.

[Scorcher]

10 minutes ago, Paul_1978 said:

This one Scorcher.

Thanks Paul, it was from a coldie as I expected! As mb above has said, that run was an unsettled outlier.

[Sky Full]

Irrespective of whether we get a warmer period towards the end of the month, I am still waiting to see how far east the track of storm Helene will get, and what strength the winds will be.  This is what is currently showing for the 18th September:

ECM       

UKMO    

GFS       

GEM      

Helene is confidently shown to be situated in the western approaches and this will be of interest to anyone contemplating a ferry trip to or from Ireland or northern France around this time.  My bet is that there will be cancelled services.  Anyone who lives in 'the west' is also bound to be interested in the maximum wind gusts over this period as the trees still have all their leaves and if there is a last minute change in direction further east and/or a strengthening of the overall wind speeds, disruption on land could also become a factor.  I'm hoping that the storm will weaken, of course.  Bring on that 'Indian Summer' instead......

 

[Singularity]

 

Met Office issue a warning that includes western parts of mainland UK and right on cue, GFS 06z adjusts furthest west of any run from that model so far.

Serious hat on - the MO are right to include western UK as there's not only hurricane Helene but also subtropical storm Joyce consider as well when it comes to the track that this bout of unusually strong winds (for the time of year at least) will take. 

 

Longer-term, the signal for a notable build of high pressure from the southwest keeps turning up, but the details are varying a lot;

  

With only a weak, stuttering tropical cycle to guide things, the knock-on effects of variations in tropical/subtropical cyclone movement are especially large, and it's hard to place much confidence in any particular solution, particularly given that the models keep seeing more of a tropical cycle emerging in the near-term than is actually observed; a persistent error that's been ongoing since mid-August.

[Sky Full]

Further to Singularity's excellent post above, the GFS 0.25 is showing this for 0200hrs 18th September:

Max Wind Gusts:            

The storm is shown tracking just off the west coast of Ireland, albeit giving that coast a battering.

However, the GFS 0.25 Parallel is showing this just six hours later:

Average Wind Speeds:  

Max Wind Gusts:           

The latter 2 charts indicate sustained winds in my location at up to 70mph and gusts at or over 90mph.   At this time of year, these conditions might be quite, if not very, disruptive.  It is becoming important to know which of these two closely related models might be right, or if it's neither.  Not being knowledgeable about the GFS, can anyone explain to me why the parallel model could vary so much from its older sibling?

 

[Mike Poole]

51 minutes ago, Sky Full said:

Further to Singularity's excellent post above, the GFS 0.25 is showing this for 0200hrs 18th September:

Max Wind Gusts:            

The storm is shown tracking just off the west coast of Ireland, albeit giving that coast a battering.

However, the GFS 0.25 Parallel is showing this just six hours later:

Average Wind Speeds:  

Max Wind Gusts:           

The latter 2 charts indicate sustained winds in my location at up to 70mph and gusts at or over 90mph.   At this time of year, these conditions might be quite, if not very, disruptive.  It is becoming important to know which of these two closely related models might be right, or if it's neither.  Not being knowledgeable about the GFS, can anyone explain to me why the parallel model could vary so much from its older sibling?

 

In the past, a parallel GFS has been the same model being trialled with an upgrade of some sort.  Not so this time, it's actually a trial of a new model chosen to succeed the GFS called the FV3 (still presumably fed with GFS input data) - although it will still be called GFS if/when it takes over - the GFS is dead, long live the GFS!

However, I suspect that the difference between models is a secondary uncertainty here, and the difference between the two runs is due to the actual significant uncertainty over the track of Helene, and over the intensity when and if it hits the UK.

[feb1991blizzard]

Got a feeling a short early blast might be on offer early Oct, a lot of runs have looked favourable for teeing up a Northerly lately.

[Sky Full]

2 minutes ago, Mike Poole said:

In the past, a parallel GFS has been the same model being trialled with an upgrade of some sort.  Not so this time, it's actually a trial of a new model chosen to succeed the GFS called the FV3 (still presumably fed with GFS input data) - although it will still be called GFS if/when it takes over - the GFS is dead, long live the GFS!

However, I suspect that the difference between models is a secondary uncertainty here, and the difference between the two runs is due to the actual significant uncertainty over the track of Helene, and over the intensity when and if it hits the UK.

Many thanks, Mike.  Assuming that computer model upgrades are tweeks to existing software and not completely new programming, it just goes to show that a tiny adjustment in the input can result in quite significant differences to the output.  I was more puzzled that these differences could occur in such a relatively short timescale, but i guess this storm really is that unpredictable....  I will just have to wait until Sunday to see whether my roof is at risk.....  Not much I could do about it, anyway!  

[The PIT]

Mmmmmm what to believe

[SmartD]

1 hour ago, Sky Full said:

  ....Not being knowledgeable about the GFS, can anyone explain to me why the parallel model could vary so much from its older sibling?

 

The difference between the GFS OP and GFS FV3 para is striking. Likely it's due to the different handling of the trough to the west, but treatment of convection with ex-Helene may be an issue as well. Here is the pressure of the PV (potential vorticity) =2 surface T120 VT 12 UTC 18Z September. The filament of PV extending from the large scale trough west and north of the UK and curving back to the Azores  is key to the evolution of ex-Helene and is handled differently by FV3 along with the trough-ridge itself which appears sharper and less progressive in the OP run consistent with the weaker development.  Unfortunately I  couldn't retrieve MSLP from the Para file but it produces a much weaker system farther east.

       

All the global models can struggle with trough extension- typically producing less sharp features than those verified, esp at T120. Therefore one should treat individual model solutions with a great deal of caution. However, on climatology grounds (comparing with Debbie (1961), Gordon (2006) and Ophelia (2017)) I would favour the western OP solution and this may not properly depict the intensity and trough interaction yet.

David

Edited September 14, 2018 by SmartD

[Frosty.]

Looking at the Gfs 12z operational, there's very warm low to mid 20's celsius for a time next week further s / e and then a bit further ahead another summery spell for a time as high pressure builds in..nice☺

Edited September 14, 2018 by Frosty.

[Frosty.]

The GEFS 12z mean also indicates high pressure building in for a time during late september bringing a spell of very pleasant conditions across most of the uk, especially further south.☺

Edited September 14, 2018 by Frosty.

[SMU]

ECM 192 >> 216 >>240 

A very persistent theme being modelled for the past 48 hours with some form of atlantic ridge- very inlike last september - again indicitive of a weakened jet flow...

Cmon- this is our year..

Edited September 14, 2018 by Steve Murr

[Frosty.]

Following a generally warm first half, the second half of the Ecm 12z turns distinctly chilly and more autumnal with some cold nights, especially further north, cold enough for a touch of frost in places.

Edited September 14, 2018 by Frosty.

[Allseasons-Si]

30 minutes ago, Steve Murr said:

ECM 192 >> 216 >>240 

A very persistent theme being modelled for the past 48 hours with some form of atlantic ridge- very inlike last september - again indicitive of a weakened jet flow...

Cmon- this is our year..

We would be screaming the place down if these charts was showing up in winter,pv displaced well west of Greenland

Edited September 14, 2018 by Allseasons-si

[Allseasons-Si]

The ecm is a cold outlier on the ens

(London)

ecm mean at 192-240 shows the Azures high influencing  the weather from the SW esp the south and southeast of the uk

the latest cpc 500 mb outlook reflects this

6-10 and 8-14 day anomoly's.

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

 

 

 

Edited September 14, 2018 by Allseasons-si

[feb1991blizzard]

Atlantic ridge and possible N'ly becoming a recurrent theme.

[Sky Full]

For me, the GEM has the best looking evolution from +96 to +240 - a very nice end to the month of September:

.   

It will be very interesting to see if we can pull off another warm and settled spell before October - or even during October.

[feb1991blizzard]

Mid Atlantic amplification going on on the 6z GFS still and now the ensembles starting to catch on - a few nearly touching -5c already.