Model Output Discussion - cold spell to end Autumn

[West is Best]

2 hours ago, Quicksilver1989 said:

So, another day and yet another messy picture

To summarise we have some very cold air from the NW on Friday but what next?

Do we get a soft exit from the cold spell and see the cold air over Europe over parts of the UK still?

Or do we get a hard exit with the colder European air displaced with lots of rain?

That is the £50 billion dollar question and the key is the area of low pressure entering northern Ireland. There is no agreement yet.


The option I’d like to see is to remain in more European based cold. Maybe we should look to Norway and build some high pressure there and import the colder European air. It would take a bit of time to get the really cold uppers, but it would be cold enough at least for a good taste of winter. The advantage of this pattern is heights in the Atlantic are less important so cold over Greenland may not get in the way of a wintry spell of weather here.

The last place we want to look to is Switzerland for high pressure. Late GFS 00z shows this scenario and it may be possible. Though this is a long way out and it may not be as mild as that.

These are just a set of scenarios which could occur under the current synoptic situation. In the end the British weather will do what the British weather does. It’s the will of the weather gods. Lets hope they change their mind from the zonality of recent years and we remain in the cold European air!

Brilliant

[comet]

The last couple of days I had been pondering why the models were showing a slider when all models were showing pressure falling to the north. It did not make sense and either the models were wrong and we would see deeper lows moving in a more West to East direction or pressure to the north was being modelled wrong and pressure would remain higher to the north and thus the slider. It now looks as though it was the latter. The question I am now asking is if the models were wrong with heights to the north at just 3to4 days out then there is a high chance they are wrong at 6and 7 days out etc.

[bluearmy]

4 minutes ago, ArHu3 said:

The ensemble for de Bilt has much less spread, so London is probably on some warm/cold battleground 

I imagine it’s more to do with many Dutch members having a slack continental feed which is possibly more from the sw over London delivering less cold temps 

[pyrotech]

19 minutes ago, bluearmy said:

Can’t really assess ec as two charts are for midnight rather than noon. We know yesterday’s 00z run was far ne 

here are the two missing ec ones

Thanks i was rushing and i try to do things without my reading glasses, your adding of those two much appreciated , its interesting to see the corrections between the two models

[ArHu3]

1 hour ago, ShortWaveHell said:

Would the models associate high pressure with warmer temps ? Wondering if this is a high pressure coming from the continent (east)  

On the east/south side of a low pressure area you get warm south/west winds, on the north /west side cold east/north winds 

[Methuselah]

Well, whatever the heck falls from the sky between Thursday and Monday, one thing seems certain (judging by what the models/UKmet are all saying): that the next two (possibly more) weeks will give us just about the best wintry synoptics we've seen in years...

Best not get to hung-up on the day-to-day minutiae? Just take it as it comes. Or doesn't!

[Seasonality]

14 minutes ago, comet said:

The last couple of days I had been pondering why the models were showing a slider when all models were showing pressure falling to the north. It did not make sense and either the models were wrong and we would see deeper lows moving in a more West to East direction or pressure to the north was being modelled wrong and pressure would remain higher to the north and thus the slider. It now looks as though it was the latter. The question I am now asking is if the models were wrong with heights to the north at just 3to4 days out then there is a high chance they are wrong at 6and 7 days out etc.

There is a high chance they are inaccurate at 6 and 7 days at the best of times!

[Barking_Mad]

5 minutes ago, Seasonality said:

There is a high chance they are inaccurate at 6 and 7 days at the best of times!

Fixed: There is a high chance they are inaccurate at 6 and 7 hours at the best of times!

 

[georgiedre]

4 hours ago, Steve Murr said:

Morning -  I see yer more drama on the 06z ... Time after time its 'South west'... yet   Some members still question why some of us document in advance the reasons why-

The models are now 'resolving' the visibility of the ridge that sits to the south of iceland at T96 that little 'sausage' is becoming more & more apparent which is in turn increasing the trough disruption & track-

The low is elongating so much that we are now also beginning to lose the onshore flow that for the S/SW & SE is the killer

here side by side is the 18z V 06z

you will now the negative tilt & south Easterly flow on the 06z v the more positive 18z ...

Its all getting rather interesting... 

Wales > Cotswolds in the £££ seat or just the hills in Devon if it holds true to form & history!!

S

Surely the snow accumulation map should have loads of snow cover over North Wales by 6am Friday??

[georgiedre]

2 hours ago, Steve Murr said:

Back to the here & now & before the 12s set off on their hopecasting voyage - here is the snowfall accum chart for T48 Euro 4-

A pretty impressive coverage for the UK in particular the favoured spots of the NW midlands - but Ireland ! wheres our Irish contingent - snow all the way down to dublin-

Maybe even a few flurries in London again !

This is the on I quoted. Not sure why the other one appeared

[phil nw.]

Good afternoon all,

It will likely get very busy once the evening charts start churning out so it will be great if all posts in here are meaningful model discussion.This will certainly make the thread better reading for all of us.

Remember if your post is just general chat or banter with no serious attempt to discuss the charts then please head to the other threads-- links provided by Paul at the top of the page.

Thanks everyone.

 

Edited December 6, 2017 by phil nw.

[SMU]

19 minutes ago, georgiedre said:

This is the on I quoted. Not sure why the other one appeared

The EURO 4 is probably picking up the signlal for some embedded trough activity but not the signal for the convective showers...

[SMU]

2 hours ago, bluearmy said:

Steve - wouldn’t you want to wait for the 12z to make the judgement that there is only a 100 mile envelope north of the 06z ? 

Well yes I guess - & I would normaly go with the safety of the full 12z suite however confidence in the 06z Ensemble undepinned by consistency plus history makes it a 'considered' call-

Wheres @nick sussex it used to be now we would be waiting for the GME to come out before the GFS to see any apparent changes-

All- Focus on the slider from Fri-Sat onward will move to the High res models- The NME/APERGE etc to see what they are saying.

current upper depths are at an elevated 15-20Cm because there expected to be a pivot point - where if your in the NW quadrent you could do very well...

S

[pyrotech]

Steve i think your on the money there, Sea temps of plus 11c

Upper air temperature of minus 8 -10 c

Plenty of convection as it rides over such a contrasting temperature and with it i would not be surprised to see some sferics

To us lot - Thundersnow

Met office warnings seem to indicate that Mogreps is riding somewhere near GFS in its move Southwards

I hope IF pops in on the forum tonight to give his views

[Paul_1978]

Latest NAO and AO graphs. Some very negative AO members....

Edited December 6, 2017 by Paul_1978

[nick sussex]

In terms of the latest output to come out only one so far is the NAM.

The 12hrs has altered the jet track out of the USA and we only get the upstream view but this looks more condusive downstream to a southwards correction compared to its earlier 06hrs.

I'll stress though this is the mesoscale model normally just for the USA so treat with caution!

[Methuselah]

15 minutes ago, Steve Murr said:

The EURO 4 is probably picking up the signlal for some embedded trough activity but not the signal for the convective showers...

It'll be interesting to see if the embedded trough beefs up showers running down the East coast, too...

[Daniel*]

Pretty good GEFS agreement to take our slider further S. Confidence increasing on this? Let’s see what the 12z brings.

[Jayfromcardiff]

7 minutes ago, Daniel* said:

Pretty good GEFS agreement to take our slider further S. Confidence increasing on this? Let’s see what the 12z brings.

Based the above, which areas have best chance of snow? Would you say midlands south?

 

My gut feeling is that it'll end up in France by Sunday.

[shaky]

Very similar to the 06z so far!!ever so slightly less amplification ahead of the slider but  you really cant tell!!

[Ali1977]

Just now, Jayfromcardiff said:

Based the above, which areas have best chance of snow? Would you say midlands south?

 

My gut feeling is that it'll end up in France by Sunday.

Agreed, we don't want much more of a move South or everyone could miss out. I'm hoping for a slight North correction to give us more of a chance for somewhere in the UK to get a dump 

[karlos1983]

So far the track looks identical to the 06z, very early days though 

Icon tracks the low through N Ireland!

[radiohead]

Correction slightly further north of the 06Z on the 12Z at T78.

[Ali1977]

Slider slightly further North going off T78, just need more moisture to boost those totals 

[karlos1983]

2 minutes ago, Ali1977 said:

Slider slightly further North going off T78, just need more moisture to boost those totals 

looks almost identical to me