Model Output Discussion - cold spell to end Autumn

[Dennis]

beautyfull RELOAD

[Derecho]

The most important thing is getting the heights over Greenland which clearly is the case on the GFS which is great to see.

Then it becomes a case of cold northerly v mild south westerly but such is the strength of the Greenland high the northerly is forced southwards. Great run for northern areas this.

UKMO will likely go down a very similar path, if the pressure over Spain were to be weaker then forecast it really would be exciting but lets see.

Will post a lot more later.

[frosty ground]

1 minute ago, CreweCold said:

Extremely.

How the preceding pattern plays out will dictate whether we see freezing temps and snow or whether we're cracking the BBQ out and up in the teens Celsius. It's that finely balanced. 

Yep, not sure following the mean charts will be of much use in a binary situation like that.

[Met4Cast]

I'd argue it's not "finely balanced" and that cold is almost odds on. The models are fluctuating all over the place with shortwaves and such but the one, strong signal that remains every single time is for Northern Blocking around the Greenland area. 

We can argue shortwaves/split flows until we're blue in the face but whatever the models do with them seems to always end up in the same place, heights over Greenland and cold air moving South across the UK.

12z would be a major snowfall event at 204 with a channel low feature running Eastwards.

[Cheshire Freeze]

Just now, frosty ground said:

Yep, not sure following the mean charts will be of much use in a binary situation like that.

Yeah

Ensemble means will be next to useless. The ops will lead the way here with the progression of getting enough heights to Greenland. Buckle in for the ride because it will be a bumpy one!

[Day 10]

After the last few years we can't grumble 'IF' we end up in this kind of situation.

[MKN]

2 minutes ago, Daniel Smith said:

Cold air flooding Southwards

Confidence of a Greenland high I'd put at 70% given the strong signal for one now. Confidence is actually higher in the extended than it is in the medium with regards to how we get there.

Id say its still a 50/50 that we get from +96 to +144 in a way that benefits long term. It wouldnt take much of a change from the 12z for us to be looking at southerly winds with the high sat over France. If in 3 days time we are seeing the charts like the 12z leads to after this time then we can start looking forward to cold and possible snow.

[Man With Beard]

Cold vs Mild battle, somewhere between Warrington and Worcester:

    

A step up for cold, even from the 06Z

UKMO, on the other hand, very finely balanced at T144

[Met4Cast]

1 minute ago, CreweCold said:

Yeah

Ensemble means will be next to useless. The ops will lead the way here with the progression of getting enough heights to Greenland. Buckle in for the ride because it will be a bumpy one!

Exactly what I was saying earlier, ensembles will give absolutely no idea of the way forward in a situation like this, they're lower resolution and will struggle even more to resolve the energy and shortwave locations. 

Ops leading the way and we're off to a cracking start with the 12z. ECM will hopefully back the GFS tonight and then we're 3/3. UKMO 144 would lead to the same heights building to the North.

[Weathizard]

3 minutes ago, Daniel Smith said:

I'd argue it's not "finely balanced" and that cold is almost odds on. The models are fluctuating all over the place with shortwaves and such but the one, strong signal that remains every single time is for Northern Blocking around the Greenland area. 

We can argue shortwaves/split flows until we're blue in the face but whatever the models do with them seems to always end up in the same place, heights over Greenland and cold air moving South across the UK.

12z would be a major snowfall event at 204 with a channel low feature running Eastwards.

Trust me if you think any GH setup isn't finely balanced, you are very wrong! We've been stung hundreds of times by this before, we could equally end up with a drab ECM like solution.

No offence to you of course I just disagree, especially with how this GH is coming about sypnotically it's fraught with danger.

[Cheshire Freeze]

1 minute ago, Daniel Smith said:

Exactly what I was saying earlier, ensembles will give absolutely no idea of the way forward in a situation like this, they're lower resolution and will struggle even more to resolve the energy and shortwave locations. 

Ops leading the way and we're off to a cracking start with the 12z. ECM will hopefully back the GFS tonight and then we're 3/3. UKMO 144 would lead to the same heights building to the North.

The UKMO is actually more finely balance than you think. Heights are slightly lower over Greenland than they are on the GFS at day 6.

[nick sussex]

Great stuff from the GFS so far with the cold air undercuttng the precip.

The UKMO has also improved so after a traumatic morning sighs of relief all round however it’s not a done deal and still a few hurdles to overcome.

I’d prefer to see the block centered a bit further east but that’s a way out so could change.

 

[Cheshire Freeze]

Just now, Weathizard said:

Trust me if you think any GH setup isn't finely balanced, you are very wrong! We've been stung hundreds of times by this before, we could equally end up with a drab ECM like solution.

No offence to you of course I just disagree, especially with how this GH is coming about sypnotically it's fraught with danger.

The 12z GFS is a prime example of what I was saying yesterday...look at the 3 wave pincer attack on the trop vortex owing to enough heights around the Greenland locale. If this fails, we're struggling longer term as it's a longer route back to cold.

[Daniel*]

UKMO and GFS 12z looking good to me just those pesky positive geopotential heights to our S are nibbling at me a tad. That ridge being further east not even by a great deal would help dig troughing further S.

Edited November 28, 2017 by Daniel*

[Derecho]

That is an impressively unstable northerly there. A huge pool of colder air to our north this time, if the ECM is on board with the retrogression there is some serious potential further down the line. Going to be a gripping few days watching the model output.

[radiohead]

Brrr that's cold!

[Daniel*]

Just now, radiohead said:

Brrr that's cold!

With a west based -NAO too....

[karlos1983]

Oh my GFS you naughty thing you 

[Man With Beard]

1 minute ago, Daniel* said:

With a west based -NAO too....

Hasn't stopped the cold getting to us, though

[Summer Sun]

Comparing the past 3 GFS updates today for December 5th at 19:00

[terrier]

Well looking at the gfs and to an extent the ukmo they are both fraught with danger. We need almost everything to go perfect to get the cold in place and potentially snowfall. Think I will go with worst case scenario then won’t be disappointed.

[Mokidugway]

2 minutes ago, radiohead said:

Brrr that's cold!

Yep it's cold but a normal chilly day for the south 

[tight isobar]

Seem to be evolving into west based NAO..

Yet still under some distinctly full on polar air!!!

Gfs12z..

Need ecm on a same path this evening for assurety!!

[Daniel*]

Just now, Man With Beard said:

Hasn't stopped the cold getting to us, though

A rare occasion with that there’s more risk but it is a more cyclonic type of cold = lots of snow. 

[That ECM]

3 minutes ago, nick sussex said:

Great stuff from the GFS so far with the cold air undercuttng the precip.

The UKMO has also improved so after a traumatic morning sighs of relief all round however it’s not a done deal and still a few hurdles to overcome.

I’d prefer to see the block centered a bit further east but that’s a way out so could change.

 

The output is and has been all over the place but one consistent message has been blocking predominantly to our NW. They just want to put a block of some description in that area. Gfs is just stunning and a channel low with cold air under cutting, well it doesn't get better.