I've been pretty quiet recently (largely due to going back to work), but suffice to say things are going as expected. The pattern change on the 9th is still there and, I must say, was an excellent spot by the ECM-15 almost two weeks ago. Sustained mild weather was never an option (beyond 5% or so) after the change and as mentioned last week the choice then became whether we'd have an average spell or a colder one.
The only change since the weekend is that the colder option has become more and more likely, with it now being the odds-on favourite. There's still a small but not ignorable chance of it staying near average, but for the time being I'd go for the cold option.
There are a few things to watch out for now that cold is looking likely:

• How long will it last? Nobody knows, but a spell of several cold days is now looking probable.


• Will it snow? Almost certainly, but of course it's too far out to be specific. In the meantime, the GFS op has a prolonged rain-to-snow scenario for southern England, which would be interesting for us southerners!


• Will the pattern be self-sustaining? The models are undecided but going on recent years we'll need to watch out for trough disruption to the west. (There are several informal terms for this, "sliders", "lows going under the block" and so on). Every trough that disrupts to the west gives an extension to the cold.


• The upper high is part of the puzzle. It's related to the trough disruption (which is itself related to the jet) but for a quick glance the location of that upper high is important. If it sinks SE'wards it becomes harder - but not impossible! - to sustain a cold spell.


• The 528 line is less useful than usual. When we get a feed from the east during winter the lower levels tend to cool faster, meaning you get a cold, low-dewpoint "wedge" of air advected ahead of the colder upper air. This only serves to increase the likelihood of snow rather than rain. The effect of course lessens the further north you are as the sea has a greater modifying effect.

So, to sum up - watch for trough disruption (or sliders, lows under the block, lows getting shredded etc). Watch for the upper high near Scandinavia. And don't be at all surprised to see the models "wobble" more than once, as features too small to be resolved at the moment get picked up nearer the time (aka "spoiler lows", "shortwaves" etc).
The overall pattern is one which should excite cold weather fans and it will if nothing else bring a completely different feel to things than we've had so far this winter.
And as a final thing, it's the ECM which did the best with this. First to pick up the pattern change around a fortnight ago and the ensembles have been more consistent than its rivals. GEM deserves a mention too, as it's been pretty good at picking up the signal for an easterly. G(E)FS has performed relatively poorly and it's no wonder that work is currently being rushed along on a new version of the model. We'll see the results of that in April. It's also a reminder that although ensembles are the way to go, they're only as good as the base model driving them - if the base model is performing poorly, you'll get massive swings from the whole ensemble suite. Much as we've seen over the last 48 hours from GEFS!

Originally Posted by: Sasa 

Morning campers - rise and shine

Not much to add to Darren's excellent summary and although not the 'where did that come from' scenario (it was as Darren said increasingly being hinted at especially in the ECM suite), IF we do get a three day easterly blast our of this then many people will be asking some searching questions both of the models and their own judgement perhaps.

Still, let's not get too hasty - a week is an age in this business.

Originally Posted by: nsrobins 

I've been pretty quiet recently (largely due to going back to work), but suffice to say things are going as expected. The pattern change on the 9th is still there and, I must say, was an excellent spot by the ECM-15 almost two weeks ago. Sustained mild weather was never an option (beyond 5% or so) after the change and as mentioned last week the choice then became whether we'd have an average spell or a colder one.

The only change since the weekend is that the colder option has become more and more likely, with it now being the odds-on favourite. There's still a small but not ignorable chance of it staying near average, but for the time being I'd go for the cold option.

There are a few things to watch out for now that cold is looking likely:

• How long will it last? Nobody knows, but a spell of several cold days is now looking probable.


• Will it snow? Almost certainly, but of course it's too far out to be specific. In the meantime, the GFS op has a prolonged rain-to-snow scenario for southern England, which would be interesting for us southerners!


• Will the pattern be self-sustaining? The models are undecided but going on recent years we'll need to watch out for trough disruption to the west. (There are several informal terms for this, "sliders", "lows going under the block" and so on). Every trough that disrupts to the west gives an extension to the cold.


• The upper high is part of the puzzle. It's related to the trough disruption (which is itself related to the jet) but for a quick glance the location of that upper high is important. If it sinks SE'wards it becomes harder - but not impossible! - to sustain a cold spell.


• The 528 line is less useful than usual. When we get a feed from the east during winter the lower levels tend to cool faster, meaning you get a cold, low-dewpoint "wedge" of air advected ahead of the colder upper air. This only serves to increase the likelihood of snow rather than rain. The effect of course lessens the further north you are as the sea has a greater modifying effect.

So, to sum up - watch for trough disruption (or sliders, lows under the block, lows getting shredded etc). Watch for the upper high near Scandinavia. And don't be at all surprised to see the models "wobble" more than once, as features too small to be resolved at the moment get picked up nearer the time (aka "spoiler lows", "shortwaves" etc).

The overall pattern is one which should excite cold weather fans and it will if nothing else bring a completely different feel to things than we've had so far this winter.

And as a final thing, it's the ECM which did the best with this. First to pick up the pattern change around a fortnight ago and the ensembles have been more consistent than its rivals. GEM deserves a mention too, as it's been pretty good at picking up the signal for an easterly. G(E)FS has performed relatively poorly and it's no wonder that work is currently being rushed along on a new version of the model. We'll see the results of that in April. It's also a reminder that although ensembles are the way to go, they're only as good as the base model driving them - if the base model is performing poorly, you'll get massive swings from the whole ensemble suite. Much as we've seen over the last 48 hours from GEFS!

 

Originally Posted by: Sasa 

ECM 96 is looking very good.

WAA over the UK, Arctic High nosing southwards, jet on a sliding SE'wards track, and a trough over western Siberia feeding a deep cold pool into Scandinavia.

http://www.wetterzentrale.de/pics/Recm961.gif

 

Originally Posted by: Gusty 

Well, looks as though my view that zonality would persist through January is going to be wrong (not that I am unhappy about that).
The question then is why the sudden change (assuming winter does commence next week, which now looks increasingly likely)?
Guess it is to do with the pressure rise over the Pole and the recent collapse of the vortex into north America - that has opened the door for us. No SSW this time, but I do think the change has started in the Stratosphere, with a gradual warming over the Pole leading to the eventual collapse of what was a very extreme and cold vortex. Just goes to show that the vortex being stronger and colder than usual, is no predicter of its longevity - we have had winters, especially in the 1990s, where an average vortex has kept mild zonality going all winter long.

Originally Posted by: Maunder Minimum 

As I said recently, zonality will last as long as the conditions will allow it. "Once zonality sets in, it's hard to shift" is a nonsense. In some years, it takes a large shift, other occasions, it is only a small tweek. Zonality is like a piece of string, no one knows for certain how long it is or in this case it will last.

Originally Posted by: Maunder Minimum 

 

Still, let's not get too hasty - a week is an age in this business.

Originally Posted by: nsrobins 

As I said recently, zonality will last as long as the conditions will allow it. "Once zonality sets in, it's hard to shift" is a nonsense. In some years, it takes a large shift, other occasions, it is only a small tweek. Zonality is like a piece of string, no one knows for certain how long it is or in this case it will last.

Originally Posted by: Maunder Minimum 

Something for both North and South divides

http://www.meteociel.fr/modeles/ecmwf/runs/2014010800/ECU0-216.GIF?08-12

http://www.meteociel.fr/modeles/ecmwf/runs/2014010800/ECU0-192.GIF?08-12

Remarkable how close to this time last year this may occur.

 

Originally Posted by: winterof79 

Well, looks as though my view that zonality would persist through January is going to be wrong (not that I am unhappy about that).

The question then is why the sudden change (assuming winter does commence next week, which now looks increasingly likely)?

Guess it is to do with the pressure rise over the Pole and the recent collapse of the vortex into north America - that has opened the door for us. No SSW this time, but I do think the change has started in the Stratosphere, with a gradual warming over the Pole leading to the eventual collapse of what was a very extreme and cold vortex. Just goes to show that the vortex being stronger and colder than usual, is no predicter of its longevity - we have had winters, especially in the 1990s, where an average vortex has kept mild zonality going all winter long.

Originally Posted by: Maunder Minimum 

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

OP very much in the minority milder cluster long range. Control and majority members go cold/very cold Dutch coast from day 6.

Originally Posted by: nsrobins 

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

OP very much in the minority milder cluster long range. Control and majority members go cold/very cold Dutch coast from day 6.

Originally Posted by: nsrobins 

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

OP very much in the minority milder cluster long range. Control and majority members go cold/very cold Dutch coast from day 6.

Originally Posted by: nsrobins 

Impressive

Originally Posted by: nsrobins