Model Output Discussion - Autumn arrives

[seb]

Quite the opposite. There appears to be a tendency by some to take synoptics at 8 days plus as gospel leading to conclusions such as “significant rain for all”.

The models are just that, models of different scenarios which become less reliable the further out they are.

For nearly a year now, all models have overestimated the impact of frontal systems coming from the Atlantic. Every time a decent amount of rain is shown in the Eastern half of the UK from such a system, it gets watered down and pushed back.

There has been no “force” to push those systems sufficiently across the country and that fact remains. Unless and until the Atlantic patterns go towards something we’d consider a standard setup, this won’t change. It matters not one bit if both the ECM and GFS show a monsoon over the Eastern half at >T+8, unless there is a major change in the overall Atlantic pattern, these scenarios wont verify.

 

[DR(S)NO]

3 minutes ago, seb said:

Quite the opposite. There appears to be a tendency by some to take synoptics at 8 days plus as gospel leading to conclusions such as “significant rain for all”.

The models are just that, models of different scenarios which become less reliable the further out they are.

For nearly a year now, all models have overestimated the impact of frontal systems coming from the Atlantic. Every time a decent amount of rain is shown in the Eastern half of the UK from such a system, it gets watered down and pushed back.

There has been no “force” to push those systems sufficiently across the country and that fact remains. Unless and until the Atlantic patterns go towards something we’d consider a standard setup, this won’t change. It matters not one bit if both the ECM and GFS show a monsoon over the Eastern half at >T+8, unless there is a major change in the overall Atlantic pattern, these scenarios wont verify.

 

Bit off track here, but spending billions of pounds on Supermodels has resulted in them still overestimating things then has it been a waste of money? How far ahead in forecasting accuracy terms are we than, say, the late 2000s?

[seb]

23 minutes ago, DR(S)NO said:

Bit off track here, but spending billions of pounds on Supermodels has resulted in them still overestimating things then has it been a waste of money? How far ahead in forecasting accuracy terms are we than, say, the late 2000s?

It’s much more accurate. It wouldn’t have been possible to more or less nail down a heatwave 14 days in advance. But models are based on previous data, behaviour and outcome. If something changes in way that hasn’t happened inside the period which models have access to then they’ll struggle. 
 

Of course all the investments are not only aimed at mid-range forecasting and its accuracy. Huge sums are invested in more and more accurate short term modelling which is extremely important for flooding, tornadoes, storms and so on.

[Summer8906]

4 hours ago, Mark Smithy said:

Are you sure about this though? Next weekend on the ECM does offer a brief respite but only before the next system pushes fronts across. It looks pretty cyclonic, no?

In the south, not so much - pressure is around 1015 consistently, so about average, and the isobars suggest tropical maritime so cloudy and possibly drizzly, yes, but a deluge, I doubt it. Further north a different story I guess.

4 hours ago, Mark Smithy said:

 

A long way out so much can change, including on timings.

 

 

Edited September 3, 2022 by Summer8906

[Cambrian]

The 6z GFS ensemble mean anomaly chart at day 10 is showing average heights for the UK and Ireland, and an almost symmetrical hemispheric divide across the pole, with above average heights extending from Alaska, through the far north of Canada to Greenland and Iceland, into the Atlantic. Below average heights extend from Siberia to Scandinavia, down into Central Europe. 

Though there is still a slight leaning towards above average heights overall, this is a much more balanced anomaly chart than we were seeing a few weeks ago, in that we’ve lost those wall to wall above average heights from the late summer.

  

The mean chart is hinting at Atlantic ridging, a Scandinavian trough, and a cross-polar flow that we would be very interested to see in about three months time! As it is, the setup is looking to deliver average to below average T850s to many parts of Northern Europe including the UK and Ireland - most of Europe has cooled right down - and this perhaps is a pattern worth keeping an eye on.

The 0z ECM mean charts are broadly similar, but keep the Atlantic low a bit more prominently and further west. 

 

So while in hemispheric terms it’s all still very slow moving, and the nascent PV is taking form only timidly - after such a globally hot summer, there are some seasonal signals for early autumn solidly appearing in the model outputs for Europe now in the form of more normal heights, uppers and temperatures. 

[jamesthemonkeh]

2 hours ago, seb said:

For nearly a year now, all models have overestimated the impact of frontal systems coming from the Atlantic. Every time a decent amount of rain is shown in the Eastern half of the UK from such a system, it gets watered down and pushed back.

 

I'm going off vague memory of a year's models here, but I think we haven't had much in the way of frontal systems projected?  Most of the projected rain, at least over the previous few months has come from cut-off lows or similar to our south-west.

Generally I think the models are excellent at predicting frontal rain.  It's the more convective stuff they struggle to pinpoint...understandably.

[Frosty.]

My take on the ECMWF 0z ensemble mean, for sure, it looks like becoming increasingly autumnal as a trough moves in and becomes slow moving over the u k bringing a cyclonic mixture of sunshine and showers, some heavy and thundery with even some longer spells of occasionally heavy rain…however, in the drier and brighter slots it should feel warm with temperatures into the low 20’’s celsius, but cool under persistent rain…BUT, later on the trough fills and pressure rises somewhat, ergo, becoming drier with more in the way of sunny spells and pleasantly warm under an essentially n / s split, for sure, summer is over but that doesn’t preclude some further fine and warm spells!? … all broad brush but my thoughts.. for now!   ️ 🌧 ⛈  

 

[Methuselah]

2 minutes ago, jon snow said:

My take on the ECMWF 0z ensemble mean, for sure, it looks like becoming increasingly autumnal as a trough moves in and becomes slow moving over the u k bringing a cyclonic mixture of sunshine and showers, some heavy and thundery with even some longer spells of occasionally heavy rain…however, in the drier and brighter slots it should feel warm with temperatures into the low 20’’s celsius, but cool under persistent rain…BUT, later on the trough fills and pressure rises somewhat, ergo, becoming drier with more in the way of sunny spells and pleasantly warm under an essentially n / s split, for sure, summer is over but that doesn’t preclude some further fine and warm spells!? … all broad brush but my thoughts.. for now!  ️ 🌧 ⛈  

 

Well, Jon -- after what seems like an eternity of azure-blue skies, sod all rain and endless bettyswollocksness -- a wee bit of something cyclonic will do nicely!

[Frosty.]

The longer term GEFS 6z mean suggests something of a north / south split..perhaps even better than that!?..

Sure I’ve been selective… ..but that’s my prerogative innit!   

 

Edited September 3, 2022 by jon snow

[Weather Enthusiast91]

9 hours ago, Summer8906 said:

That GFS 00Z really is horrendous, please someone say it's an outlier! Wettest September since at least 2000 if that comes off, I suspect and the change seems reminiscent of 1976.

We'll all be begging for dry weather by mid-month if that comes off!

Really hoping we're not going to see a repeat of autumn/winter 1976/77, or for that matter 2000/01.

I would normally agree, but we have had copious amounts of dry days since the beginning of the year. Last winter was dryer than average, as was spring and then summer. So three consecutive seasons dryer than average.

This year, I would personally be happy with a wetter than average autumn as a way to balance things out a little. Whether we like it or not, rain is essential and something we shouldn't underestimate the importance of.

 

[KTtom]

41 minutes ago, Weather Enthusiast91 said:

I would normally agree, but we have had copious amounts of dry days since the beginning of the year. Last winter was dryer than average, as was spring and then summer. So three consecutive seasons dryer than average.

This year, I would personally be happy with a wetter than average autumn as a way to balance things out a little. Whether we like it or not, rain is essential and something we shouldn't underestimate the importance of.

 

Totally agree, so long as it stays warm for a bit, it wont do anyone any favours having to put the heating on in September! As we move into another season, can we remember, although we live on a small island, there are big differences in weather as Autumnal conditions set in to western areas where its been cool and wet today central and eastern areas remain warm and dry for now...we are all guilty on IMBY posts but constant posts about who said what are tedious. Its a model discussion and interpritation thread.  

[damianslaw]

Just taking the UKMO this evening, the current low pressure is still forecast to be influencing the UK in 7 days time, that's one lengthy low pressure system hanging about... all indicative of the fact we have a cut off low.

7 days is as far out as I will comment right now. Until then an unsettled outlook, rain, showers, some drier brighter spells in places, often quite warm relative to early Sept average even under the rain and cloud. Windy at times as well. Quite a lively spell of weather ahead, difficult to pinpoint where the heaviest rain will fall.

GFS is equally unsettled if not more so, but rather than keeping the current low over the UK, it shifts it east on Thursday followed by another deep low with tropical origins in time for next weekend - which would result in a very wet one indeed.

Edited September 3, 2022 by damianslaw

[richie3846]

31 minutes ago, damianslaw said:

Just taking the UKMO this evening, the current low pressure is still forecast to be influencing the UK in 7 days time, that's one lengthy low pressure system hanging about... all indicative of the fact we have a cut off low.

7 days is as far out as I will comment right now. Until then an unsettled outlook, rain, showers, some drier brighter spells in places, often quite warm relative to early Sept average even under the rain and cloud. Windy at times as well. Quite a lively spell of weather ahead, difficult to pinpoint where the heaviest rain will fall.

GFS is equally unsettled if not more so, but rather than keeping the current low over the UK, it shifts it east on Thursday followed by another deep low with tropical origins in time for next weekend - which would result in a very wet one indeed.

The progression of Danielle is totally unclear at the moment. The models have it going over the UK pushing this low out, or even going up to Greenland while passing far west of the UK. These outcomes are radically different, I'd say even 7 days out is a long time with all that going on. These tropical depressions can often be seen taking an erratic and unpredictable path. 

[stodge]

Yes, GFS 12Z brings the remnants of ex-Hurricane Danielle across the British Isles as quite a deep and complex LP for early September with a lot of rain for southern and western parts in particular.

The following ex-hurricane takes a more traditional northward path and is absorbed into the main Atlantic trough.

[minus10]

1 hour ago, damianslaw said:

Just taking the UKMO this evening, the current low pressure is still forecast to be influencing the UK in 7 days time, that's one lengthy low pressure system hanging about... all indicative of the fact we have a cut off low.

7 days is as far out as I will comment right now. Until then an unsettled outlook, rain, showers, some drier brighter spells in places, often quite warm relative to early Sept average even under the rain and cloud. Windy at times as well. Quite a lively spell of weather ahead, difficult to pinpoint where the heaviest rain will fall.

GFS is equally unsettled if not more so, but rather than keeping the current low over the UK, it shifts it east on Thursday followed by another deep low with tropical origins in time for next weekend - which would result in a very wet one indeed.

Yes...interesting run from the gfs 12z. 

The ex tropical Danielle is joined by a trough coming down from the north west again...

Although this is at the bottom of the ens at this time..

 

Towards the end of the run the gfs puts us back in a sw flow with hp to the se..

All in all not a cold run by any means....

A lot going on synoptically...be interesting to see how this plays out...hopefully there will be some rain too....

Edited September 3, 2022 by minus10

[Newberryone]

Again one can see by today’s 12z Ecm that it’s holding steadfast in its medium range output indicating a steady improvement from next weekend. Danielle will more than likely result in bringing about renewed ridging from the Azores resulting in subsequent Atlantic depressions being deflected well away to the northwest. An indicator that would suggest a north/south split going further into September with conditions best described as mixed.

[Tn9]

10 hours ago, DR(S)NO said:

Bit off track here, but spending billions of pounds on Supermodels has resulted in them still overestimating things then has it been a waste of money? How far ahead in forecasting accuracy terms are we than, say, the late 2000s?

The SHIPS model is a good example of what has become sensor based system instead of seeing it  for yourself ....(Statistical hurrcane Intensity Prediction Scheme )...climate models to a degree (excuse the pun) get loads of mis calculations..we actually know  they are under estimating  lots of things ...statistics only represent past scenarios..its not that simple anymore and those models also take data  from dynamical models ..but obervers on our out posts see much different things happening 

.so something else is at play (maybe positive feed back ) 

[Iceman2606]

GFS 18z: The Great Storm of 1987 anyone?

[KTtom]

Its been some time since wind and rain has kept me awake at night, looks like a repeat performance tonight looking at the latest fax. Northern Ireland looks to be having a torrid time looking at the latest radar. Maybe some rainnreaching the south east by Tuesday.

 

 

 

Edited September 4, 2022 by KTtom

[Newberryone]

Thankfully It would appear Danielle will become just a shallow area of low pressure having largely filled as it tracks harmlessly across the English Channel or indeed perhaps further south come next Saturday to be followed by renewed ridging from the south. Mixed conditions thereafter with weak weather systems occasionally brushing off northwestern areas with the driest conditions reserved for the south/southeast. All in all, very standard fare for early autumn.

[minus10]

3 hours ago, KTtom said:

Its been some time since wind and rain has kept me awake at night, looks like a repeat performance tonight looking at the latest fax. Northern Ireland looks to be having a torrid time looking at the latest radar. Maybe some rainnreaching the south east by Tuesday.

 

 

 

I'll put it in my diary....

[Mark Smithy]

53 minutes ago, Newberryone said:

Thankfully It would appear Danielle will become just a shallow area of low pressure having largely filled as it tracks harmlessly across the English Channel or indeed perhaps further south come next Saturday to be followed by renewed ridging from the south. Mixed conditions thereafter with weak weather systems occasionally brushing off northwestern areas with the driest conditions reserved for the south/southeast. All in all, very standard fare for early autumn.

I don't think these model outputs are presenting a pattern that we have seen this early in September for some time? What is a particular shock to the system, albeit not yet in the south-east, is just how quickly it changed from summer to autumn. Often September throws up plenty of settled, warm and even hot days. It may do so yet.

Re. ex tropical storm Danielle, you are right about the wind intensity. However, these ex hurricanes and storms usually produce anything BUT 'very standard fare for early autumn'. It may not have intensity of wind but they invariably carry high levels of humidity and precipitation, with often very 'heavy' atmospherics. You can see this well on the 0z GFS and especially the 0z ECM:

That track across southern Britain is not supported by the aforementioned ECM, which has it tracking across southern France, but look what happens when it reinvigorates over the Alps:

[Summer8906]

GFS 00Z seems to keep cyclonic weather going right until the 20th, albeit with a northerly component later (so more sunshine and lower DP, with less damp hanging around between systems, so perhaps more pleasant) and then at the very end of the run, yet another low threatening in the Atlantic. If that comes off exactly as it is, I suspect flooding, and not drought, will be the major concern by the equinox and we'll be looking at one of the wettest Septembers on record. The repeated track of lows right across the southern UK has the look of summers 2007 and 2012 to me.

18Z is arguably better overall for usable weather: the current spell of poor weather culminates with a major storm around the 14th (the third low), but following that, as often happens after really big storms (didn't it turn dry after Eunice and Franklin?), the bad weather blows itself out and we end up with a sustained settled spell until the end of the run on the 19th. Either way, GFS suggests that any usable weather in September will be confined to the second half of the month.

Is anyone else having problems with ECM? I just can't get charts after the 9th to show, either for last night's 12Z or today's 00Z. A shame as I'm rather hoping ECM contradicts GFS...

Edited September 4, 2022 by Summer8906

[Captain Shortwave]

Both the ECM and GEM show an improvement into week 2. 
   
 

On fact both show some very warm air heading northwards that could see a last hurrah of summer-like conditions. A long way off though for any confidence and the GFS is not interested.

Ens - ECM/GFS

   
 

Neither overly keen on something more than a weak transient ridge before stronger westerlies push through. 
Rainfall potential for the week;

ECM

 

GFS

So rainfall is certainly there, though whilst there are bands of rain that move east/north east. The large rainfall totals suggest localised downpours will do some of the heavy lifting, so no slam dunk for rain in the east at the moment where there is the highest risk of fronts fizzling out and showers being less likely to develop.

[mushymanrob]

Its a given that any ex hurricane/tropical storm might upset the applecart... but these anomaly suites suggest a very normal, average, british september through the mid month period.