Model Output Discussion - Mid Summer Onwards

[Cambrian]

Ah, that’s very nice on the 12z ECM op.

That low off eastern Canada (at day 5) plays an important part in the evolution, by cleaving the Atlantic heights apart from the Canadian heights that spawned them (at day 6) and phasing with the base of the Greenland trough (at day 7).

  

This allows the same Atlantic heights that pull us into a northerly flow for the weekend at day 5, and pay us a visit by day 7 to help us dry out with a little high just for the UK and Ireland…

  

to then extend north to link up with polar heights through Svalbard on day 8, build further and move east towards Scandinavia by day 9 and 10. 

The result is that the cold air that floods south doesn’t get dislodged for several days. Generally dry with light winds, any clear nights are going to suddenly feel very sharp indeed. 

[WYorksWeather]

22 minutes ago, seb said:

Cooler yes but nothing to suggest something cold and also not for long. 
Blended output for my location literally has 12 days of temps between 12 and 17 degrees. That’s far from cold and still mainly above October average.

I think taking the period overall you may be right. Again I make no judgement at this stage regarding the length of the cold spell - it's too soon. The most I'd be prepared to say is that it's warm up until Wednesday, bit of a N/S battleground through Friday, then cooler than average for most from Friday through Sunday and possibly quite cold further north. Agree though that at your location you're likely to be closer to average than most of us.

Beyond Sunday is still FI I think. GFS ensembles are out and it is a massive outlier once it goes into FI, but the broad pattern through Sunday is reasonably well supported:

[Mike Poole]

ECM clusters tonight staunch support for the scandi high T192-T240:

Two clusters, but both heading the same way.  T264+:

Cluster 1 has extraordinary synoptics, you’d want to see this in January!  Worth looking in more detail at the representative perturbation 32 at T312:

Cluster 2 also remains very blocked.  

All very interesting, as summers last hurrah until Wednesday then ushers in a real change…

[LetItSnow!]

With all this warmth it's nice to see the possibility of an unusually strong cold pool even if we don't tap into it! What with this eternal summerless summer 

[seb]

34 minutes ago, WYorksWeather said:

I think taking the period overall you may be right. Again I make no judgement at this stage regarding the length of the cold spell - it's too soon. The most I'd be prepared to say is that it's warm up until Wednesday, bit of a N/S battleground through Friday, then cooler than average for most from Friday through Sunday and possibly quite cold further north. Agree though that at your location you're likely to be closer to average than most of us.

Beyond Sunday is still FI I think. GFS ensembles are out and it is a massive outlier once it goes into FI, but the broad pattern through Sunday is reasonably well supported:

Oh yes, all FI and more so this year. But looking at that scatter probabilities look to be above average for now. Too early to make any calls.

[Daniel*]

4 minutes ago, seb said:

Oh yes, all FI and more so this year. But looking at that scatter probabilities look to be above average for now. Too early to make any calls.

Open your eyes Seb  

[snowsummer]

14 minutes ago, Mike Poole said:

ECM clusters tonight staunch support for the scandi high T192-T240:

Two clusters, but both heading the same way.  T264+:

Cluster 1 has extraordinary synoptics, you’d want to see this in January!  Worth looking in more detail at the representative perturbation 32 at T312:

Cluster 2 also remains very blocked.  

All very interesting, as summers last hurrah until Wednesday then ushers in a real change…

On 08/10/2023 at 02:24, Kirkcaldy Weather said:

 

Is it time for a new thread now....the hunt for early cold?

[Crackerjack]

3 hours ago, 78/79 said:

First Mother in law would probably disagree with you, she reckons her broomstick is freezing at that time of year .

Careful what you say as I can feel a cold ‘Spell’ coming your way

[Rain All Night]

8 hours ago, RainAllNight said:

The GEFS 6z run is even more determined than its predecessor that the ECM and GEM ensembles are giving us the wrong impression about an upcoming Scandi high spell, suggesting instead that we are going to have lows coming in and getting stuck over us due to heights further east, with heights only building further north late in the run, at which point the lows start digging to the southeast.

ECM: dry

GEM: probably dry

GEFS: 

For what it's worth, the EC46 this morning seemed to think that the northern blocking may stick around for a while once it arrives.

[damianslaw]

Mmm seem to be in a rather abnormal state at present, the current exceptional warmth and slow moving frontal rain making wave trough features north half of the UK, not your typical atlantic zonal onslaught.

Now the models are going for a northerly followed by potential scandi high.

All very interesting if you want to see switcharound synoptics, more akin to what we see often in Spring, but not early-mid autumn.

October 2023 could end up being a month of high variety. 

 

[seb]

7 hours ago, Daniel* said:

Open your eyes Seb  

My eyes are wide open and they see wide confidence levels, average or above average temps and when looking at ensembles and comparing models a whole lot uncertainty across the board.

Whoever wants to be foolish enough to make a call on what the weather will look like exactly from Sunday onwards, be my guest. I’ll stick to cooler, somewhat more unsettled but unlikely to be cold or below average.

Again, probabilities, confidence levels and many other factors matter. Personal preference does not.

[MattH]

1 hour ago, seb said:

My eyes are wide open and they see wide confidence levels, average or above average temps and when looking at ensembles and comparing models a whole lot uncertainty across the board.

Whoever wants to be foolish enough to make a call on what the weather will look like exactly from Sunday onwards, be my guest. I’ll stick to cooler, somewhat more unsettled but unlikely to be cold or below average.

Again, probabilities, confidence levels and many other factors matter. Personal preference does not.

Morning. These kinds of posts here are the ones that just don't help people learn or gain clarity on the outlook and the content here is highly misleading.

There are no 'wide confidence levels', whatever that means, and using terminology like 'foolish' when it comes to making forecasting predictions at a time frame that actually requires a forecast, is foolish in itself...

That aside back to the forecast and what we see is good clarity on the initial transition to cooler weather mid-week, this has been well documented and forecasted for several days. The process for the south is obviously delayed because of the frontal wave and system from the SW that brings the risk of a sharp thermal boundary and resultant significant rainfall totals on Friday. Therefore, it is a more 'step change' to cooler weather across parts of England and Wales, a more straightforward one elsewhere.

The building ridge to the W and NW then ushers in an air mass that couldn't be any more different than what is in place now (850mb temps fall 20 degrees, see below!) and temperatures WILL end up below average, widely, by this weekend with overnight frosts, especially ground frosts and depending on the longevity of the air mass from the N or NW, snow showers are likely across the hills of Scotland as well. The flow is likely to be cut off and we then end up with a building area of high pressure over the UK early next week (cold and crisp) which then looks to become a potential Scandinavia high, it is at that point confidence falls away more significantly.

The story for the next 5 to 7 days can be told very well on the 00Z GFS ENS... N England is used in this instance as the example.

Regards, Matt.

[Nick2373]

00z still shows the decline in temps to something very wet for Friday the 13th, then the trend for something colder from the 14th-18th which brings a drier interlude after that looks like the temps will go just above average with mixed spells of showers, but that's way out in FI at the minute 

[NewEra21]

1 minute ago, seb said:

No one is claiming the "cold plunge" isn't there. The result is however nothing cold for the majority of the country. It'll be cooler and a bit more seasonal but the details, even as close as Saturday, are not clear at this point. Anything from temps never dropping below October average to 3-4 days of daytime highs around 10 degrees is on the cards. But above all, it's nothing extraordinary as some seem to want to portray it. 

Of course it isn’t going to be incredibly cold, it’s still early October. But I’d say many places will be below average this weekend, which is pretty significant in itself from what we’ve seen so far this month.

Seasonal with the potential of frosts is something we rarely see in October of late, so that excites me and I’m sure it does others too.

[Paul]

Interesting set of GEFS ensemble vs climatic average maps this morning - say goodbye to the positive temperature anomalies for a bit, at least, if these are correct.

  

[Rain All Night]

12 hours ago, RainAllNight said:

The ECM certainly seems to be the most serious about this omega Scandi high business.

Not sure I like this take as much!

[Lukesluckybunch]

latest ECM mean not hardly as good..suggesting more a euro high..then scandi

[alexisj9]

5 minutes ago, Lukesluckybunch said:

latest ECM mean not hardly as good..suggesting more a euro high..then scandi

 

6 minutes ago, RainAllNight said:

Not sure I like this take as much!

Low to the nw much closer.

[Lukesluckybunch]

1 minute ago, alexisj9 said:

 

Low to the nw much closer.

yes the trejectory not like how we want it

[seb]

1 hour ago, MattH said:

Morning. These kinds of posts here are the ones that just don't help people learn or gain clarity on the outlook and the content here is highly misleading.

There are no 'wide confidence levels', whatever that means, and using terminology like 'foolish' when it comes to making forecasting predictions at a time frame that actually requires a forecast, is foolish in itself...

That aside back to the forecast and what we see is good clarity on the initial transition to cooler weather mid-week, this has been well documented and forecasted for several days. The process for the south is obviously delayed because of the frontal wave and system from the SW that brings the risk of a sharp thermal boundary and resultant significant rainfall totals on Friday. Therefore, it is a more 'step change' to cooler weather across parts of England and Wales, a more straightforward one elsewhere.

The building ridge to the W and NW then ushers in an air mass that couldn't be any more different than what is in place now (850mb temps fall 20 degrees, see below!) and temperatures WILL end up below average, widely, by this weekend with overnight frosts, especially ground frosts and depending on the longevity of the air mass from the N or NW, snow showers are likely across the hills of Scotland as well. The flow is likely to be cut off and we then end up with a building area of high pressure over the UK early next week (cold and crisp) which then looks to become a potential Scandinavia high, it is at that point confidence falls away more significantly.

The story for the next 5 to 7 days can be told very well on the 00Z GFS ENS... N England is used in this instance as the example.

Regards, Matt.

You are free to disagree with my assessment, just like anyone else. This is however a discussion so I don't see the need for your labelling of posts as misleading.

If you wish to nail down your forecast despite everything shown, then that is your prerogative.

The generally accepted definition of "wide confidence level" is higher uncertainty. Where uncertainty is high, as it arguably currently is x-model at a much earlier point than what we are used to (and as it has been for months), it is foolish to to state that x will happen on Monday, which is what some members have done and which is what I referred to in my post. 

Whenever such a scenario presents itself then forecasters apply terms such a "likely", "probably" or something like "more likely ... than"; they often also add "confidence is low" or "confidence is lower than usual".

At this moment in time, it is almost certain that temperatures will drop to more seasonal values after Friday, albeit even at this range it is not clear whether they will be below October average for a time or not (this is more likely in central and northern parts). Any output for the period post Monday currently suffers from increasing uncertainty, between models and also from run to run as demonstrated by the 00z ECM vs it's 12z run; this uncertainty increases more than usual the further into the modelled period we go.

This uncertainty is perfectly reflected in the latest MetO update for 15-24 Oct from this morning which states that temps (nationwide) will be a little below average at the start of that period, rising to little above average. The extended outlook (through to 7 Nov), although from yesterday afternoon, states that temps are generally expected to be a little above average with frost less likely than expected for the time of year.

While you may disagree with that assessment, I happen to fully agree (and I'm not someone to hold back with criticism of the MetO). As it stands, temps will drop but the likelihood of anything cold is low. In fact I wouldn't even be surprised if save for some areas in Scotland and possibly the very far north of England, we will not see any frost even on the "coldest" nights in the next 7-10 days.

[Rain All Night]

10 hours ago, RainAllNight said:

ECM: dry

GEM: probably dry

GEFS: 

For what it's worth, the EC46 this morning seemed to think that the northern blocking may stick around for a while once it arrives.

This morning, the GEFS is now more willing to follow the other two models and get that block up to a higher latitude and more quickly, but it still finds a way to get at least some of us wet (thinking of myself here) by letting lows dig down past us to the southeast.

Days 7, 10, 13:

[CoventryWeather]

1 hour ago, RainAllNight said:

Not sure I like this take as much!

Clusters 264hrs+ are lovely. Bank that one in Dec/Jan. 

[matty40s]

1 hour ago, Paul said:

Interesting set of GEFS ensemble vs climatic average maps this morning - say goodbye to the positive temperature anomalies for a bit, at least, if these are correct.

  

Time to wax the skis  up there...

[Sky Full]

Looks like a new “atmospheric river” of rain will be affecting Wales, the South West and/or parts of the Midlands over the next few days.   Here are the rainfall accumulation charts up to Monday midnight from the main models courtesy of Meteologix.com….

UKMO                        

ECM

GFS

GEM

North West Scotland also getting another soaking.

[Captain Shortwave]

This coming weekend does look decidedly cooler thanks to a polar maritime airmass.

 

It does look like there is potential for some widespread grass frosts and wintry showers over higher ground. It will be a big change from the current conditions (especially in the south).

Next week looks rather uncertain, the surface high looks quite chilly (At least to start with), if we can fully undercut the ridge that will push eastwards then a cut off high and an easterly flow is possible (this could keep conditions pretty chilly and showers could be quite potent given the warm sea temperatures), however it is also possible that winds could back southerly again and see temperatures recover back to near normal with dry conditions in the east (I think this weekend will properly end the summer like conditions that have persevered over Western Europe through most of the Autumn so far).